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AE7F
12-27-2011, 10:39 PM
Anyone ever tried to build one?

KC5FM
12-28-2011, 01:05 AM
Anyone ever tried to build one?

I have not but here are plans (http://www.dxzone.com/cgi-bin/dir/search.cgi?query=Log%20Periodic), if you want to try yourself.

73

W9GB
12-28-2011, 01:31 AM
TennaDyne (Roger Greenfield, WB8NDC) now located in Michigan still makes Log-Periodic antennas :-)
http://www.tennadyne.com/index.html

Chuck Brainard, KA1PM was the founder of TennaDyne and sold the business to Roger in 2004.
http://www.tennadyne.com/about_Roger.htm

w9gb

AE7F
12-28-2011, 02:00 AM
Very cool, thanks. This is interesting:
81979


I have not but here are plans (http://www.dxzone.com/cgi-bin/dir/search.cgi?query=Log%20Periodic), if you want to try yourself.

73

AE7F
12-28-2011, 02:03 AM
Thanks. I have been looking at Tennadyne antennas for awhile (antenna comparisons.xls (http://singlebirds.com/files/antenna comparisons.xls)). You can see that I found the T6 to be a very, very nice antenna for the price and have been looking around for one.


TennaDyne (Roger Greenfield, WB8NDC) now located in Michigan still makes Log-Periodic antennas :-)
http://www.tennadyne.com/index.html

Chuck Brainard, KA1PM was the founder of TennaDyne and sold the business to Roger in 2004.
http://www.tennadyne.com/about_Roger.htm

w9gb

WB2WIK
12-28-2011, 02:24 AM
Unless you have access to the materials for very discounted cost, it would be hard to beat the price of even a new Tennadyne.

Seamless aluminum 6061T6 alloy tubing is expensive, and the T6 uses a lot of it, including 24' of extruded square boom stock and about 160 feet of round tubing of various snug fitting diameters, plus several precision cut insulating blocks, thick machined PVC insulating blocks at the mast mounting point, etc. It would make an interesting project, but certainly not an inexpensive one.

AE7F
12-28-2011, 07:33 PM
Yeah, their pricing is good for the T6 but one does wonder what materials would cost for the aforementioned LP design.

http://www.texastowers.com/aluminum_.htm


Unless you have access to the materials for very discounted cost, it would be hard to beat the price of even a new Tennadyne.

Seamless aluminum 6061T6 alloy tubing is expensive, and the T6 uses a lot of it, including 24' of extruded square boom stock and about 160 feet of round tubing of various snug fitting diameters, plus several precision cut insulating blocks, thick machined PVC insulating blocks at the mast mounting point, etc. It would make an interesting project, but certainly not an inexpensive one.

KO6WB
12-28-2011, 08:37 PM
The ARRL Antenna Handbook has detailed instructions also at least mine does. You could try that. You might also want to pick up a copy of the handbook, the older ones are somewhat better but I don't know if they have the LP plans in them.
Hope this helps
73
Gary

VK2FXXX
12-28-2011, 11:03 PM
You might consider a wire type LPDA?
Maybe a 40ft boom and 12+ elements.
See Cebick W4RNL site for some big LPDA designs.
If it does not work well take it all down and use the boom as another antenna mast!!
The rear spreaders as the basis for a rotatable dipole etc.........
I would love to try one one day.Might need a bigger back yard though!
Good luck
Brendan

WB2WIK
12-28-2011, 11:07 PM
Yeah, their pricing is good for the T6 but one does wonder what materials would cost for the aforementioned LP design.

http://www.texastowers.com/aluminum_.htm

Using those costs, the aluminum tubing would run about $280. Then you'd have to cut it in three dozen places and drill it it 36 places to join the elements, and 12 more places in the booms to insert the elements. You'd still have to create mast to boom brackets, PVC insulating spacers, and the big PVC mast clamp insulators, plus add several dozen SS screws, bolts, etc.

It could probably be built for about $350 worth of parts, not considering shipping costs for the tubing.

VK2FXXX
12-29-2011, 02:49 AM
Re my earlier post ,maybe something similar to this?
http://www.antenna.be/tci-521.pdf

Brendan

KO6WB
12-29-2011, 04:02 AM
That is quite an antenna. It gives some additional thought to what is possible. There was a design that was featured in QST that used a spider type of support. Can't really remember when it was published and it has been awhile. The antenna was made from wire and it was a LPDA. At the time I was interested in that concept but I haven't had the room to put something like that up.
May be things will change, who knows?
73
Gary

AE7F
12-29-2011, 05:33 AM
LPDA... interesting.... found some stuff that looks cheap but might pack a punch...


You might consider a wire type LPDA?
Maybe a 40ft boom and 12+ elements.
See Cebick W4RNL site for some big LPDA designs.
If it does not work well take it all down and use the boom as another antenna mast!!
The rear spreaders as the basis for a rotatable dipole etc.........
I would love to try one one day.Might need a bigger back yard though!
Good luck
Brendan

AE7F
12-29-2011, 05:36 AM
You just made it sound not too bad!

Hardest part for me is that I can't see the aluminum tubing. If I could go pick sections off the shelf at the hardware store, knowing what I was getting, and that it would fit together.... If I find a local source for tubing watch out!

The T6 is a great price as is. But add shipping and suggested hardware and chokes/baluns and the DIY vs commercial price gap starts to grow.


Using those costs, the aluminum tubing would run about $280. Then you'd have to cut it in three dozen places and drill it it 36 places to join the elements, and 12 more places in the booms to insert the elements. You'd still have to create mast to boom brackets, PVC insulating spacers, and the big PVC mast clamp insulators, plus add several dozen SS screws, bolts, etc.

It could probably be built for about $350 worth of parts, not considering shipping costs for the tubing.

VK2FXXX
12-29-2011, 06:53 AM
I had a whole bookmark folder full of links to LPDA stuff.
Ill see if I can find the article about building a wire LPDA
I have an old Australian made LPDA under the house that was given to me by a generous Ham.
Just a little 6 element job ,needs some new centre insulators and tlc.
I like the Idea of having 1 directional antenna for say 7-30mhz,
Even with the compromises.
Brendan

VK2FXXX
12-29-2011, 07:36 AM
Found one.
Just type "telerana" into your favourite search engine.
http://people.seas.harvard.edu/~pdeotare/logperiodic.pdf
Enjoy
Brendan

NH7RO
12-29-2011, 08:27 AM
I had a whole bookmark folder full of links to LPDA stuff.
Ill see if I can find the article about building a wire LPDA
I have an old Australian made LPDA under the house that was given to me by a generous Ham.
Just a little 6 element job ,needs some new centre insulators and tlc.
I like the Idea of having 1 directional antenna for say 7-30mhz,
Even with the compromises.
Brendan

Thanks for posting the Telerana link; seeing photos made me realize that that is certainly an easily doable DIY 5-band single feedline antenna, isn't it? I believe this same or similar design wire LPDA is also in the ARRL Antenna Book (sans photos), too. Probably wouldn't be too costly to make; the fiberglass spreaders and the welded steel hub would be the only parts costing much.

With a 400-ohm characteristic impedance I wonder if a 9-1 balun would be better than the recommended 4-1 balun at the feedpoint?

Thanks again for further food for [antenna] thought.

73, Jeff

WB2WIK
12-29-2011, 04:57 PM
The T6 is cheap to ship because it comes in a very short carton. That's why it's a whole lot of pieces to put together.

Mine shipped to Los Angeles and I think the shipping was about $25. The T8 comes in the same size carton, it's just more pieces.

You'd have to build a choke balun for any kind of LPDA whether you bought it or built it, so that's a draw. I just use the "RF choke" type current balun made of coax, as they recommend. It costs about $8 or so to build it. There isn't any extra hardware to buy, it comes with all the hardware you could need except for the balun and feedline.

I build VHF-UHF antennas pretty often but wouldn't try building an HF LPDA unless I had a big machine shop and a lot of time. To pull this off with hand tools would just be too much work, for me.:o

AE7F
12-29-2011, 05:48 PM
Appreciate the input. Always helps.

Drill press, chop saw, jig saw? Metal blades.... Shouldn't be too bad at all.

However, will probably just buy a T6 or try out some wire arrays in the meantime.


The T6 is cheap to ship because it comes in a very short carton. That's why it's a whole lot of pieces to put together.

Mine shipped to Los Angeles and I think the shipping was about $25. The T8 comes in the same size carton, it's just more pieces.

You'd have to build a choke balun for any kind of LPDA whether you bought it or built it, so that's a draw. I just use the "RF choke" type current balun made of coax, as they recommend. It costs about $8 or so to build it. There isn't any extra hardware to buy, it comes with all the hardware you could need except for the balun and feedline.

I build VHF-UHF antennas pretty often but wouldn't try building an HF LPDA unless I had a big machine shop and a lot of time. To pull this off with hand tools would just be too much work, for me.:o

AE7F
12-29-2011, 05:54 PM
Yup, stumbled onto that link last night. Really cool. And *cheap*. Great way to try out the LP concept first...


Found one.
Just type "telerana" into your favourite search engine.
http://people.seas.harvard.edu/~pdeotare/logperiodic.pdf
Enjoy
Brendan

WB2WIK
12-29-2011, 05:55 PM
Appreciate the input. Always helps.

Drill press, chop saw, jig saw? Metal blades.... Shouldn't be too bad at all.

However, will probably just buy a T6 or try out some wire arrays in the meantime.

Some of the beauty of the commercial offering is the machined insulators they use. They press-fit snugly into the booms where the mast clamps are to keep the booms from compressing (they're solid PVC, evidently CNC'd from blocks) and then there are more of them between the booms to keep the boom spacing consistent and add mechanical strength. The booms-to-mast clamps include two large machined solid PVC insulator blocks (which again, appear to be CNC'd from solid larger blocks) that conform to the boom dimensions and the mast they clamp to. This could probably all be done with hand tools, but it would certainly be a lot of work and probably not come out as well.

N3OX
12-29-2011, 05:56 PM
Drill press, chop saw,


If you have a drill press and a chop saw with a metal blade that is a long way toward making a LPDA a reasonable homebrew job :D

KO6WB
12-29-2011, 06:12 PM
Yup, the Telerana was the one that was in QST. Glad Bredan found it. I couldn't remember the name of it but the moment I saw the name in Bredan's post it was like instant recall.
It's an interesting design.
73
Gary

K1ZJH
12-29-2011, 06:30 PM
I think Steve nailed it; the cost of duplicating a complex log antenna might not be worth it. But, anyone contemplating a homebrew
design might consider using wire elements instead of aluminum tubing. Think "Titanex":

http://www.mydarc.de/dl6ip/Log-Periodic-Ant.html

That would cut the costs considerably, and is the approach I'd take.

Pete

W8JI
12-29-2011, 06:52 PM
DX Engineering sells great insulators for things like this, not cheap but good. My 20 meter Yagi has their insulators.

NA0AA
12-29-2011, 07:02 PM
Another option of course, if you had room would be to build wire LPDA's and hang 'em as slopers off a central tower - one of the ARRL antenna books has a design for that. I mean, you could probably build four wire LPDA's for the cost of a single rotatable one [maybe the telerana excepted?].

AE7F
12-29-2011, 07:10 PM
Really nice. Nail. Head. Hammer.

Their stuff is not sub $1k though and I doubt they release the design for homebrewers.


I think Steve nailed it; the cost of duplicating a complex log antenna might not be worth it. But, anyone contemplating a homebrew
design might consider using wire elements instead of aluminum tubing. Think "Titanex":

http://www.mydarc.de/dl6ip/Log-Periodic-Ant.html

That would cut the costs considerably, and is the approach I'd take.

Pete

AE7F
12-30-2011, 01:20 AM
I went through the Telerana document. It appears to be a document created by senior college students in India. They did a nice job and I'm sure it worked. They detailed quite a few things but I didn't see anywhere that they listed their actual element length, spacing, feeder length, and support lengths. They did list the overall length of rope and wire needed.

I have the 1985 ARRL Antenna Book and indeed found reference to the LPDA. It has steps you can take to calculate the details. If I could get some assistance from some knowledgeable folks on here on working out the details, I think I'd be willing to try a build and post pics and details.

WB2WIK
12-30-2011, 01:26 AM
I'd be really frustrated here using any kind of non-rotatable antenna. FOUR gain antennas each having HPBWs of 90 degrees, with a remote switch, might be almost okay; but I never know what direction I want to work, it could be anywhere.

Problem with beams having HPBWs of 90 degrees is they cannot have much gain; if they did, the beamwidths would be narrower.:p

NN5AA
12-30-2011, 01:13 PM
Ben , here's a link to a handy Java design program. All lengths specified are in meters.


http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=16289


There's also a decent article in the May 1965 issue of '73' magazine by VE3AHU(SK-Mar 02-2005) A.E. Blick , has some charts with actual dimensions listed for the component parts by frequencies.


73, NN5AA


A 100% Fully Functioning Boat Anchor !!

AC0H
12-30-2011, 03:31 PM
http://www.realhamradio.com/Log_Periodic.htm

NN5AA
12-30-2011, 03:38 PM
Bob, excellent & detailed article!! Great info!



73, Vince--NN5AA

A 100% Fully Functioning Boat Anchor !!

AE7F
12-30-2011, 04:55 PM
Thank you very much. I will play with it to see what I can figure out and post back. The difference here is that this calculator does not factor in element angles. I believe I read that angling the elements can increase gain on LPDA antennas.

I will also check out the '73 article.


Ben , here's a link to a handy Java design program. All lengths specified are in meters.


http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=16289


There's also a decent article in the May 1965 issue of '73' magazine by VE3AHU(SK-Mar 02-2005) A.E. Blick , has some charts with actual dimensions listed for the component parts by frequencies.


73, NN5AA


A 100% Fully Functioning Boat Anchor !!

AE7F
12-30-2011, 05:00 PM
Very nice. I will also study it in more depth. Quite detailed. Thanks.


http://www.realhamradio.com/Log_Periodic.htm

AE7F
12-30-2011, 09:10 PM
Okay, I went to http://glendash.com/Dash_of_EMC/Log_Periodic/Log_Periodic.htm and using Figure 3, decided on a Tao of 0.80 and a Sigma of 0.14. These values are chosen to acheive good gain (6.5-7db) and average beamwidth. Then, I chose a design frequency of 14-30mhz for the antenna.

Having enough information, I plugged in the numbers here:
http://www.fortunecity.com/skyscraper/jolt/345/LogCalc.html

The calculator produced the following (lengths are in meters - L is element length, d is element spacing):
Number of elements (n): 9
Axial Length: 14.850274013981094

L R d
--------------------------------------------------------------
1 : 12.7457141 17.84400095 3.568799978
2 : 10.1965714 14.27520097 2.855040025
3 : 8.15725730 11.42016095 2.284032054
4 : 6.52580593 9.136128896 1.827225670
5 : 5.22064482 7.308903226 1.461780558
6 : 4.17651592 5.847122668 1.169424463
7 : 3.34121278 4.677698204 0.935539585
8 : 2.67297027 3.742158619 0.748431679
9 : 2.13837624 2.993726939 0.598745352

I'm still evaluating things but can someone verify Axial Length for me? Does this mean this antenna needs a boom of 14.85 meters (~48.7ft) in length? And the longest element is 12.74 meters (~41.8ft)?

That's a monster of an antenna....

Changing Tao to 0.82 and Sigma to 0.10 created a smaller footprint:
Number of elements (n): 9
Axial Length: 11.070388563829225

L R d
-------------------------------------------------------------------------------
1 : 12.5232857 13.91476164 2.504657196
2 : 10.2690942 11.41010445 2.053818882
3 : 8.42065722 9.356285568 1.684131469
4 : 6.90493886 7.672154099 1.380987792
5 : 5.66204981 6.291166306 1.132409980
6 : 4.64288080 5.158756326 0.928576175
7 : 3.80716223 4.230180150 0.761432457
8 : 3.12187300 3.468747693 0.624374609
9 : 2.55993583 2.844373083 0.511987175

Axial Length of 36.32ft with a longest element of around 41ft. Looks similar to an ASL-2010. Am I correct in reading Figure 3 located here (http://glendash.com/Dash_of_EMC/Log_Periodic/Log_Periodic.htm) that this design would still yield between 6.5 and 7db?

Repeating the process to try and get a smaller footprint....
Number of elements (n): 9
Axial Length: 8.856310521140095

L R d
-------------------------------------------------------------------------------------
1 : 12.5232857 11.13180890 2.003725682
2 : 10.2690942 9.128083221 1.643055045
3 : 8.42065722 7.485028176 1.347305125
4 : 6.90493886 6.137723050 1.104790193
5 : 5.66204981 5.032932857 0.905927950
6 : 4.64288080 4.127004907 0.742860912
7 : 3.80716223 3.384143994 0.609145943
8 : 3.12187300 2.774998051 0.499499669
9 : 2.55993583 2.275498382 0.409589725

It looks like this last iteration might still give you around 6db of gain but with the much shorter boom than we started with, what will the estimated F/B ratio be for this spec?

AC0H
12-30-2011, 09:29 PM
Okay, I went to http://glendash.com/Dash_of_EMC/Log_Periodic/Log_Periodic.htm and using Figure 3, decided on a Tao of 0.80 and a Sigma of 0.14. These values are chosen to acheive good gain (6.5-7db) and average beamwidth. Then, I chose a design frequency of 14-30mhz for the antenna.

Having enough information, I plugged in the numbers here:
http://www.fortunecity.com/skyscraper/jolt/345/LogCalc.html

The calculator produced the following (lengths are in meters - L is element length, d is element spacing):
Number of elements (n): 9
Axial Length: 14.850274013981094

L R d
--------------------------------------------------------------
1 : 12.7457141 17.84400095 3.568799978
2 : 10.1965714 14.27520097 2.855040025
3 : 8.15725730 11.42016095 2.284032054
4 : 6.52580593 9.136128896 1.827225670
5 : 5.22064482 7.308903226 1.461780558
6 : 4.17651592 5.847122668 1.169424463
7 : 3.34121278 4.677698204 0.935539585
8 : 2.67297027 3.742158619 0.748431679
9 : 2.13837624 2.993726939 0.598745352

I'm still evaluating things but can someone verify Axial Length for me? Does this mean this antenna needs a boom of 14.85 meters (~48.7ft) in length? And the longest element is 12.74 meters (~41.8ft)?

That's a monster of an antenna....

Changing Tao to 0.82 and Sigma to 0.10 created a smaller footprint:
Number of elements (n): 9
Axial Length: 11.070388563829225

L R d
-------------------------------------------------------------------------------
1 : 12.5232857 13.91476164 2.504657196
2 : 10.2690942 11.41010445 2.053818882
3 : 8.42065722 9.356285568 1.684131469
4 : 6.90493886 7.672154099 1.380987792
5 : 5.66204981 6.291166306 1.132409980
6 : 4.64288080 5.158756326 0.928576175
7 : 3.80716223 4.230180150 0.761432457
8 : 3.12187300 3.468747693 0.624374609
9 : 2.55993583 2.844373083 0.511987175

Axial Length of 36.32ft with a longest element of around 41ft. Looks similar to an ASL-2010. Am I correct in reading Figure 3 located here (http://glendash.com/Dash_of_EMC/Log_Periodic/Log_Periodic.htm) that this design would still yield between 6.5 and 7db?

Sounds about right.
A Log needs a long boom to get the kind of forward gain you're designing for.
Those are 4-5 element yagi gain numbers.

In other words given the same boom length withoptimum number of elements and spacing, the yagi will always have higher gain.
When using a log you're giving up maximum gain and FB for frequency coverage.

AE7F
12-30-2011, 09:46 PM
Sounds about right.
A Log needs a long boom to get the kind of forward gain you're designing for.
Those are 4-5 element yagi gain numbers.

In other words given the same boom length withoptimum number of elements and spacing, the yagi will always have higher gain.
When using a log you're giving up maximum gain and FB for frequency coverage.

This is my understanding as well.

The ASL-2010 Skylog uses an 18ft boom (http://www.cushcraftamateur.com/pdffiles/ASL2010.pdf), yet they are claiming 6.4db. How are they doing that? Is it that they are using one less element (8) and different spacing?

Figure 3 (http://glendash.com/Dash_of_EMC/Log_Periodic/Log_Periodic.htm) doesn't show gain predictions for 5, 4, or 3db scenarios.... hmm.

Now.... if I could just figure out how to use EZNEC...

WB2WIK
12-30-2011, 11:11 PM
I think fussing over a dB one way or another with an HF beam is crazy.:o

I've had a lot of HF beams over the years (way too many) and in practice, you'll never, ever know the difference.

Strength, service life, serviceability, elevation above ground, ability to achieve a good impedance match over the bandwidth you're using and other things are more important. IMO, way more important.

With a good tower and an antenna that actually works, I can never tell the difference between beams that are approximately the same size. Making a log longer without adding more elements isn't useful: Logs need lots of elements. They're nothing like Yagis, at all -- I think the only similarity is they're both considered beams.:p

AE7F
12-31-2011, 12:46 AM
Thanks for the input. It's been a fun process looking at all of this stuff so far. Agree with you on the things you mention below, especially strength and service life. However, if it's a difference of 5db or 3db, and I have a huge LP in my yard just for 3db, I won't do it; I'll just build a hex for 3db. For me to even attempt a DIY log, it would have to be 5db or more. Difference of 5 and 6db and I agree.


I think fussing over a dB one way or another with an HF beam is crazy.:o

I've had a lot of HF beams over the years (way too many) and in practice, you'll never, ever know the difference.

Strength, service life, serviceability, elevation above ground, ability to achieve a good impedance match over the bandwidth you're using and other things are more important. IMO, way more important.

With a good tower and an antenna that actually works, I can never tell the difference between beams that are approximately the same size. Making a log longer without adding more elements isn't useful: Logs need lots of elements. They're nothing like Yagis, at all -- I think the only similarity is they're both considered beams.:p

WB2WIK
12-31-2011, 01:59 AM
Thanks for the input. It's been a fun process looking at all of this stuff so far. Agree with you on the things you mention below, especially strength and service life. However, if it's a difference of 5db or 3db, and I have a huge LP in my yard just for 3db, I won't do it; I'll just build a hex for 3db. For me to even attempt a DIY log, it would have to be 5db or more. Difference of 5 and 6db and I agree.

Unless the log is pretty big (the T12 on a 24' boom might qualify) I doubt you'll achieve 5-6 dB gain advantage in a log over a Hexbeam. The math just doesn't work out.

What you might achieve is broader tuning bandwidth (my log is 1.5:1 VSWR in all five ham bands above 14.0 MHz, and <2:1 on frequencies in between the bands, which might be useful for MARS or something) and some peace of mind knowing it won't fall apart even in very strong winds. But 5-6 dB extra gain over a Hexbeam? I doubt it's possible until you get to a larger log.

I've seen some of the commercial/military logs which use 70' of lattice tower for a boom and have 24-30 elements. Those are really nifty but they cost about $20K and weigh hundreds of pounds. I don't think I could do that here, but if I pick the right LOTTO numbers this week, who knows?:p

AE7F
12-31-2011, 04:21 AM
I didn't mean 5-6db more than a hex. I meant if a hex is 3.x db and I go to a lot of work to build or plop down a ton of cash for a huge LP to gain 1 or 2db more than the hex, I wouldn't do it. Too big of an antenna and too much money and/or work if the difference is negligible. However, if a hex is 3.x and a decent log is 6.x, now we're talking. I wasn't expecting anything to be 5-6 over the hex, which would be 8-9db total gain. Hope that clears that up.

Now... we've talked about the figures spit out by the calculator but what if I were to use wire for the elements instead of aluminum tube? I don't know all of the math behind the calculator but is the use of wire going to reduce the bandwidth per band? I can do a lot of experimenting with wire before I spend the same amount as I would with aluminum tube. Plus, I would have less wind area and load and if the antenna came down it would be a ball of wire instead of a pile of aluminum scrap.

Bottom line is what kind of monkeywrench is thrown into the mix when going from tube to wire?


Unless the log is pretty big (the T12 on a 24' boom might qualify) I doubt you'll achieve 5-6 dB gain advantage in a log over a Hexbeam. The math just doesn't work out.

What you might achieve is broader tuning bandwidth (my log is 1.5:1 VSWR in all five ham bands above 14.0 MHz, and <2:1 on frequencies in between the bands, which might be useful for MARS or something) and some peace of mind knowing it won't fall apart even in very strong winds. But 5-6 dB extra gain over a Hexbeam? I doubt it's possible until you get to a larger log.

I've seen some of the commercial/military logs which use 70' of lattice tower for a boom and have 24-30 elements. Those are really nifty but they cost about $20K and weigh hundreds of pounds. I don't think I could do that here, but if I pick the right LOTTO numbers this week, who knows?:p

AE7F
12-31-2011, 04:26 AM
Found another calculator:
http://www.arcticpeak.com/antennapages/LPDA.htm

AE7F
12-31-2011, 07:10 AM
More questions. The Telerana antenna (http://people.seas.harvard.edu/~pdeotare/logperiodic.pdf) has swept elements. Assume antenna X and antenna Y are identical except antenna X uses swept elements. What is the difference performance-wise and how is the sweep calculated? Swept elements would help reduce footprint.

Also, many antennas like the Telerana use fiberglass spreaders. Some hex builders have successfully used PVC. I think you could clear coat the PVC and it would work fine, providing it was properly guyed. Comments?

So the main costs in an LPDA as I see it would be ~400ft of wire, who knows how much rope, a quad spreader hub, and spreaders, especially if fiberglass.

Commercial fiberglass spreaders and quad hubs are expensive and I think if used, would drive the cost too high.

Let's say you used PVC spreaders and even a PVC quad joint, then guy properly to even out tension. Very lightweight and flexible. Wonder if you could do it this "cheap way" for less than $250?

NH7RO
12-31-2011, 09:35 AM
I'm not so sure about using a PVC quad joint for the hub but then we'll never know if no one tries in the first place.

Maybe a 15m to 10m LPA would work with PVC spreaders and such but I suspect that a 20m to 10m version would be too big and unwieldy for the most part. I suppose if you were on a deserted island in a desperate situation (and already had these materials on hand to build an antenna with that you could use to call for help with) then yes, this would be a viable---but probably not long lasting antenna solution.

On the other hand, I don't mean to diiscourage you, Ben as I have often wondered the same kind of questions myself.

I seldom have the kind of budget that would easily facilitate a monster beam of any sort so the wire Yagis, Hexbeams and Log Periodic Arrays fascinate me to no end.

If I were you I might further investigate home-brewing with fiberglass spreaders obtained from an outfit such as Max Gain Systems---IIRC their prices are fairly reasonable and the hub might still be made using something like a canopy frame centerpiece (available at most hardware stores) or something welded to order at minimal expense.

Others here may have a more knowledgeable answer to your swept elements gain difference but I suspect the construction method and materials used will play a more important role with such a huge beam as this. If the fiberglass is more expensive than you like perhaps a combination of PVC, well-varnished wood and some crucial fiberglass parts might work out instead.

I am enjoying this train of thought and focus on the LPAs and I might very well build one myself after I relocate next year (all depends on the actual new QTH and what's feasible there---yet I'm increasingly tempted to just pull the trigger on a KIO hex beforehand so as to be ready soon after the move with a kind of does-it-all antenna already in hand).

Getting back to your last question---I think $250 or $300 for the materials might well be in the ballpark for such a beast and I'm curious to see what the experts say on this. I'd also plan on budgeting for a decent length of LMR-400 as well as a well-made choke balun besides the materials for the LPA, too.

73 and Happy New Year to all,

Jeff

AE7F
12-31-2011, 04:59 PM
Very thoughtful reply, thanks.

I could always hack off 20m and make it just a little smaller. I was also thinking about swept elements vs straight and someone can correct me if I'm wrong but I think you should be able to sweep the elements as long as you keep the element spacing where it needs to be. So can't you just use the calculated values for element spacing and sweep the elements while keeping the spacing true? I haven't been able to confirm this yet or find another formula for calculating the sweep. Someone could throw it into EZNEC probably and find out what affect it would have...

Anyway, as I have seen, the majority of the cost would be in the fiberglass. I think with proper guying and tensioning PVC would work fine, albeit for maybe only a few seasons. Or, you could use 8ft fiberglass lengths coming out of the quad joint, then PVC further out.

PVC quad joint, probably not. But I think you could sandwich some pipe sections between two plates and bolt it together for the quad spider joint. Wire would be the next high cost of say $100. Then rope. Probably $250 gets you in the ballpark but this is not a permanent fixture. ??

Hmm....


I'm not so sure about using a PVC quad joint for the hub but then we'll never know if no one tries in the first place.

Maybe a 15m to 10m LPA would work with PVC spreaders and such but I suspect that a 20m to 10m version would be too big and unwieldy for the most part. I suppose if you were on a deserted island in a desperate situation (and already had these materials on hand to build an antenna with that you could use to call for help with) then yes, this would be a viable---but probably not long lasting antenna solution.

On the other hand, I don't mean to diiscourage you, Ben as I have often wondered the same kind of questions myself.

I seldom have the kind of budget that would easily facilitate a monster beam of any sort so the wire Yagis, Hexbeams and Log Periodic Arrays fascinate me to no end.

If I were you I might further investigate home-brewing with fiberglass spreaders obtained from an outfit such as Max Gain Systems---IIRC their prices are fairly reasonable and the hub might still be made using something like a canopy frame centerpiece (available at most hardware stores) or something welded to order at minimal expense.

Others here may have a more knowledgeable answer to your swept elements gain difference but I suspect the construction method and materials used will play a more important role with such a huge beam as this. If the fiberglass is more expensive than you like perhaps a combination of PVC, well-varnished wood and some crucial fiberglass parts might work out instead.

I am enjoying this train of thought and focus on the LPAs and I might very well build one myself after I relocate next year (all depends on the actual new QTH and what's feasible there---yet I'm increasingly tempted to just pull the trigger on a KIO hex beforehand so as to be ready soon after the move with a kind of does-it-all antenna already in hand).

Getting back to your last question---I think $250 or $300 for the materials might well be in the ballpark for such a beast and I'm curious to see what the experts say on this. I'd also plan on budgeting for a decent length of LMR-400 as well as a well-made choke balun besides the materials for the LPA, too.

73 and Happy New Year to all,

Jeff

N3OX
12-31-2011, 06:58 PM
Commercial fiberglass spreaders and quad hubs are expensive and I think if used, would drive the cost too high.

Fiberglass is at least three or four times stronger and three or four times stiffer than PVC for a given weight.

That doesn't mean you can't use PVC in some circumstances but I personally wouldn't sink time and effort into a beam for 20-10 and use PVC. In hindsight I also should have stepped up from cheap fiberglass crappie poles on my Moxons after the first time I broke one.

I like building antennas and I'm not one of those people who calculates things like "charging myself" for my hobby time at a rate comparable to my pay at work. But at the same time, there are some things I will never do again and trying to use PVC pipe or even the cheaper fiberglass poles that aren't designed as antenna parts as big structural parts for HF antennas are two of those things. I love building antennas but I do not like excessive antenna maintenance.

I will still recommend the cheap fiberglass crappie poles to people who want to try to build a Moxon or other simple beam for their FIRST TIME because some people need the kick in the pants about trying a beam :D

But I dunno, it makes me sad when a nice homebrew creation bites it because I skimped on initial cost or of I underestimated how long I was going to use something and it ends up costing more in the long run. PVC is cheap but it ain't free.

NH7RO
12-31-2011, 07:46 PM
Like I always say, "Quality only hurts once."

Know what you mean about using cheap materials. Maybe fine for a temporary antenna but anywhere there's severe weather and the pvc or Wal-Mart poles come crashing down.

I have used the cheap fiberglass fishing poles for 2 of my 3 Moxons with great success, however---but I always "overbuild" them from the start by using the fatter parts of longer poles for the spreaders and then use lightweight 18 ga. wire for the elements. I also give them a good spraying of cammo paint which helps them survive the occasionally intense UV radiation (it's raining here 90% of the time, so only 10% or so strong sunshine).

When I relocate to stateside in a few months I'll be taking my antenna farm with me but since we'll be renting the new QTH antenna situation may be very iffy, hence my quest for a compact 5 or 6 band beam that I might get by with mounted on a small roof tower or collapsible mast in the back yard.
I will almost hate to give up my separate Moxons as they do give me better gain and F/B than a hex from what I've read but it would be nice to have one antenna on one rotator for a change.

As for getting back to the DIY LPDA, I suggest going with Max Gain's fiberglass for the spreaders and perhaps an aluminum plate with stainless U-bolts for the hub. Wire and Dacron rope is realtively cheap and if I end up having the room and situation where I could erect such a big beast I may very well do the same (or a Spiderbeam which would sort of be the Yagi equivalent, sotospeak).

Off to work now, 73, Jeff

WB2WIK
12-31-2011, 07:50 PM
I think you'd have too much element sag using PVC supports for wire elements. Schedule 40 probably isn't strong enough, Schedule 80 is really heavy and probably still not strong enough. Just nowhere near the intended application. In building low-cost VHF antennas, I've found bamboo is actually stronger than PVC as well as lighter, and very UV resistant. But since we're not where the good bamboo grows, all the good stuff is imported and mostly available in shorter lengths. Finding 20'+ lengths of high strength bamboo isn't easy (I've looked), and it doesn't splice well at all while maintaining sufficient strength for an antenna application.

Rather than fibreglas and wire, I'd just use aluminum tubing. It's only expensive once, as opposed to other materials that are cheap lots of times.

Another advantage of using aluminum is you can use the split-boom route, so all elements are directly connected to the booms without the need for any insulators or criss-cross wire connections and other stuff that can go bad up in the air.

N0SYA
12-31-2011, 08:51 PM
http://aviolinx.com/Images/News/antenna1.jpg

AC0H
12-31-2011, 09:22 PM
That looks like one of the big logs they had at Collins in Cedar Rapids.

NH7RO
01-01-2012, 01:57 AM
.....But since we're not where the good bamboo grows, all the good stuff is imported and mostly available in shorter lengths. Finding 20'+ lengths of high strength bamboo isn't easy....

Wish I could cut a containerload of bamboo for you guys, I have an acre-sized grove of 30-40 footers growing half a mile up the road from me here. :o
Unfortunately that would be illegal as the Hawaii Dept. of Agriculture is very strict with plants and such coming/going to/from the islands.

It has come in handy for me a few times; my 20M rotatable folded dipole is mounted atop a piece I cut down to 35' (was about 42' when I felled it with several whacks of my machete but the top section was too thin and the bottom three feet was too fat to fit in my pipe mount) and my 12M dipole is also 90% bamboo.

Great stuff as Steve points out; I really should be using it more often (especially for something like a Moxon or a Cobwebb) as it's totally free for the taking in my neighborhood.

I do appreciate the strength and uniformity of commercially available antenna building materials so I'll be chomping at the bit to have Texas Towers and Max Gain Systems' aluminum tubing and telescoping fiberglass so readily available when I am stateside in a few months.

As for PVC I wouldn't use it for anything larger than a 2 element 6M quad and even there I think at least the crossboom would need to be wood or aluminum.

Wire elements are probably the key to building a less expensive but durable LPDA and that's about the only part that I'd be willing to scrimp on.

73, Jeff

WB2WIK
01-01-2012, 04:06 AM
Bamboo is terrific but doesn't grow naturally here in CA at all, that I know of. People "plant" it for yard decoration, but it doesn't thrive here at all.

It thrives in the tropics.

I visit the Philippines pretty often since my XYL is from there and it's amazing what they do with bamboo there. Entire houses are made from it. Scaffolds used for building skyscrapers are made almost entirely from bamboo. A lot of hams use it to make towers, quads, and everything else. It's "free," and it's very strong.

ALMOST makes me want to live in the tropics, but not quite. I'm allergic to humidity, it just kills me. If not for that, we could have a really good life in a place like that.

VK2FXXX
01-01-2012, 06:39 AM
Hey.
AE7F
You really should register for the Cebick site.
I remember he has about 5 or 6 LPDA models on there ,maybe more,I think a couple may have the V type elements.
http://www.cebik.com/
Brendan

AE7F
01-01-2012, 05:02 PM
Fiberglass is at least three or four times stronger and three or four times stiffer than PVC for a given weight.

And a lot more expensive too.

It is nonetheless disappointing to look at a homebrew design and after adding fiberglass and a commercial hub, your not really saving any over the commercial design. A T6 at $519 or a home brew (with fiberglass and commercial hub) at like $400? I guess the advantage would be you could have wire elements for different wind loading...



I love building antennas but I do not like excessive antenna maintenance.


Yeah, this would be a huge disadvantage of wire/rope beams...

AE7F
01-01-2012, 05:54 PM
Like I always say, "Quality only hurts once."

As for getting back to the DIY LPDA, I suggest going with Max Gain's fiberglass for the spreaders and perhaps an aluminum plate with stainless U-bolts for the hub. Wire and Dacron rope is realtively cheap and if I end up having the room and situation where I could erect such a big beast I may very well do the same (or a Spiderbeam which would sort of be the Yagi equivalent, sotospeak).

Off to work now, 73, Jeff

Well, correct me if I'm wrong but when I was looking at the fiberglass spreaders, in consideration of the last 20-10m iteration of the design calculator, I would need like 80ft of it, or 20 on all sides of the quad joint.

Here is their site:
http://www.mgs4u.com/fiberglass-cubical-quad-spreaders.htm

I was looking at the Type 3 spreader:
"•Type 3 consists of the same two tubes as the Type 1 spreader, plus one 8 ft. length of 1" OD (0.125" wall) grey fiberglass tube. This yields a spreader with a usable length of up to 21 ft.!!! (Allowing for 1 ft. of 1" OD tube to be epoxied into the bottom of the 1" OD tube for reinforcement.) MORE than enough for 30 Meters!!!
Approximate Weight: 8.0 lbs; Color: Grey; Price: $36.90 per spreader"

So we are looking at 32lbs of fiberglass weight and $147 bucks of fiberglass, not counting shipping. Throw on $100 for 400ft of wire and $60 for 300ft of rope and we are already over $300. Add insulators, clamps, shipping and maybe $350. Now throw on a $60 dollar quad joint. Hmm, a $519 T6 doesn't sound so bad.

On the other hand, if there is a way to get less expensive materials, a $250 antenna might be worth a try.

PVC sags, is not very UV resistant, etc. Most say it will not and does not work, yet I have talked to a small number of hexbeam builders who built with PVC and it is working fine so far. We are all waiting to see how many seasons they hold up.

I think the advantage of the hex design with PVC is that the supports are always under tension. My idea of a LP made of PVC spreaders is that you have a strong vertical support above the quad. You guy the PVC spreaders every so many feet, tying them back to the main vertical support. You do this equally on all sides. If you do it right, all of them support each other and the kevlar ropes, capable of supporting a hundred pounds or so, take the stress.

So we are talking about 20ft lengths of pipe. Guy say, every 5ft back to the vertical support. Do this on all 4 sides. Not even the telerana antenna was guyed this substantially but the supports are clearly tensioned to each other. They used pole vaulting poles. (http://people.seas.harvard.edu/~pdeotare/logperiodic.pdf)

I think you would want a nice spreader joint regardless. I like the one the telerana group welded up because the spreaders slide into long tubes. I think longer support tubes would really help with PVC and you certainly need a strong quad joint because I think that's where the majority of the highest stress would be.

If you guys can think of a less expensive way to use something other than PVC, shoot. For example, less expensive wire than .027/ft, less expensive fiberglass, etc.

I did have the thought of using their Type 1 spreaders:
"•Type 1 consists of one 8 ft. length of 1" OD and one 8 ft. length of 1" OD round fiberglass tube both having 0.125" wall. The 1" tube snugly-but-easily telescopes in-side the larger tube. Using a recommended 12" overlap yields a usable length of 15 feet...more than enough for 20M!! A foot of this extra length may be easily cut (with a hacksaw) from the 1" OD tube, and epoxied inside the bottom of the 1" OD tube. This yields a full " wall thickness(!) at the point of greatest stress...e.g. where the clamps secure the spreaders to the spreader mounting plate-or "spider".
Approximate Weight: 4.4 lbs; Color: Grey; Price: $19.80 per spreader"

Only problem is I can only get a 30ft span this way and the last antenna iteration discussed was a little larger than this. I suppose one could slightly lengthen the 15ft spreaders with a foot or two of PVC on the ends furthest from the quad joint. This would drop spreader cost to $80. This might work for the last antenna iteration we discussed:

Number of elements (n): 9
Axial Length: 8.856310521140095

L R d
-------------------------------------------------------------------------------------
1 : 12.5232857 11.13180890 2.003725682
2 : 10.2690942 9.128083221 1.643055045
3 : 8.42065722 7.485028176 1.347305125
4 : 6.90493886 6.137723050 1.104790193
5 : 5.66204981 5.032932857 0.905927950
6 : 4.64288080 4.127004907 0.742860912
7 : 3.80716223 3.384143994 0.609145943
8 : 3.12187300 2.774998051 0.499499669
9 : 2.55993583 2.275498382 0.409589725

Now we are looking at around 17lbs of fiberglass weight and $80 bucks of fiberglass, not counting shipping. Throw on $100 for 400ft of wire and $60 for 300ft of rope and we are at $250, quad joint for $60. Add insulators, clamps, shipping and maybe $360ish?

I was pricing wire based on the spiderbeam.us site, which advertises wire at .027 per foot. Maybe I could use different wire?

Comments?

AE7F
01-01-2012, 06:02 PM
Found another calculator:
http://www.arcticpeak.com/antennapages/LPDA.htm

I think I like this calculator a little better because it gives some more pieces of information. The one thing it doesn't seem to do is allow you to provide an upper cutoff frequency.

I also am not clear on what they are doing with the "Design parametre optimal σ:" value that is automatically given. Does it change my given value of Sigma to this automatically and if so, why?

It also gives "shorting stub length."

The two calculators discussed give slightly different values and I wish I could figure out why.

AE7F
01-01-2012, 06:11 PM
Done. Looking at it right now...


Hey.
AE7F
You really should register for the Cebick site.
I remember he has about 5 or 6 LPDA models on there ,maybe more,I think a couple may have the V type elements.
http://www.cebik.com/
Brendan

NH7RO
01-01-2012, 10:23 PM
Good morning Ben; I think your wire cost could be a lot less than 27 cents/foot (also I think you wrote .027 when you meant $0.27) if you went with Home Depot 18 ga. stranded bare copper. This is what I've used for a couple of my Moxons and it works out to around 5 to 6 cents/foot (250' spool for $12.66 last time I priced it). Two spools for about $26 and you'd have a bit left over.

For rope I use a thin cammo colored dacron called Mac's Sporting Line (Google and it'll turn up) that comes in 100' spools and is available here at True Value Hardware for $9 a spool (but is a lot cheaper online). It is probably about 1/16", nearly invisible and tough as...dacron. Use it for antenna rope, guy lines for lightweight antennas, etc.

Go with the Type 1 Spreaders and extend a tiny bit with PVC or other fiberglass to make up the foot or two extra. Less weight and cost there; I would think that would be fine but who knows until it is tried? Around $80 or so for the T1s so let's call it $100 with shipping and extra bits

As for the hub I'd scrounge around a big metal supply outfit for some aluminum plate---or maybe spend $100 for a hexbeam hub and modify for 4 spreaders. There's got to be a way to keep that cost down and still have something sturdy but not too heavy. If weight isn't a big issue then steel would probably be fine as long as it was well weatherproofed/painted/galvanized.

Adding this up in my head quickly it seems like you'd be right around $250 unless I'm off somewhere; maybe even less if you fabricate a good hub for under a $100.

At any rate, seems like you're doing your homework on this and I look forward to seeing what you end up using and how you make it.

73, Jeff

AE7F
01-01-2012, 11:46 PM
Good morning Ben; I think your wire cost could be a lot less than 27 cents/foot (also I think you wrote .027 when you meant $0.27) if you went with Home Depot 18 ga. stranded bare copper. This is what I've used for a couple of my Moxons and it works out to around 5 to 6 cents/foot (250' spool for $12.66 last time I priced it). Two spools for about $26 and you'd have a bit left over.

For rope I use a thin cammo colored dacron called Mac's Sporting Line (Google and it'll turn up) that comes in 100' spools and is available here at True Value Hardware for $9 a spool (but is a lot cheaper online). It is probably about 1/16", nearly invisible and tough as...dacron. Use it for antenna rope, guy lines for lightweight antennas, etc.


These are the ideas I'm fishing for. Do you think they are strong enough? I might have to go a step up. We can get some pretty severe winds here.



Go with the Type 1 Spreaders and extend a tiny bit with PVC or other fiberglass to make up the foot or two extra. Less weight and cost there; I would think that would be fine but who knows until it is tried? Around $80 or so for the T1s so let's call it $100 with shipping and extra bits


The more I think about the MGS Type 1 spreaders, the more I think that might be the way to go. I went away from the traditional thinking about an all-aluminum log periodic because of not having enough information about pricing and fitment and so forth. If I have to give up the tube elements, I better make sure I'm getting as much performance as possible for much less cost out of the wire. So the wire can be cheap but I think as far as the designs I'm thinking of that fiberglass and a strong hub will be critical. So it's ok to spend more here. $100 is peanuts if it will hold up for a good number of years.



As for the hub I'd scrounge around a big metal supply outfit for some aluminum plate---or maybe spend $100 for a hexbeam hub and modify for 4 spreaders. There's got to be a way to keep that cost down and still have something sturdy but not too heavy. If weight isn't a big issue then steel would probably be fine as long as it was well weatherproofed/painted/galvanized.


I just obtained an Alliance model 73 rotator that I hope I can use. Weight will be important as well as wind loading because I think the specs on the model 73 are 10sq ft of wind loading. Not sure on weight. Also, this gear will be sitting on top of a crank-up militarySometime back when I was strongly considering a hex or spider beam I talked to a guy that could get me a square of aluminum for the hub for around $25 bucks. This is probably the route I will go. I would drill and clamp the same way some do with the hex beam designs. If it starts to cost near $60 for clamps and aluminum and such, I'd be better off just getting a commercial hub such as one made by Cubex here:
http://cubex.com/hard.htm

I notice it is for a 2" boom so I'd have to adapt the fiberglass spreaders to fit this hub....



Adding this up in my head quickly it seems like you'd be right around $250 unless I'm off somewhere; maybe even less if you fabricate a good hub for under a $100.

At any rate, seems like you're doing your homework on this and I look forward to seeing what you end up using and how you make it.

73, Jeff

Yeah, the idea is to come up with something for around $250 that performs well for a few years or more. Already I've learned a ton along the way...

Thanks Jeff.

AE7F
01-02-2012, 12:42 AM
Hey.
AE7F
You really should register for the Cebick site.
I remember he has about 5 or 6 LPDA models on there ,maybe more,I think a couple may have the V type elements.
http://www.cebik.com/
Brendan

That made for an enlightened study.

He modeled the differences between the swept and straight element LPDAs. He dispelled the myth that the V arrays produced more gain and showed that they actually had less F/B ratio and less gain. There was also a good description of Tau and Sigma.

Very good resource, thanks.

AE7F
01-02-2012, 12:52 AM
Pete's post got buried a ways back. This might be the design/cost key. Take a look here: http://www.mydarc.de/dl6ip/Log-Periodic-Ant.html

I can't tell what they use to mount the assembly to the mast but I can't see a fancy expensive hub anywhere. They obviously move the cross beam back, which is what I'd like to try.

After reading the information about swept/vee elements on the Cebik site, I think one should keep the elements straight if possible. At this point, something similar to the Titanex antenna is what I'm going for. Now I need more details. They say dual boom but I can't see it unless they are talking about the feed line as a boom. They also say no balun required. How did they do that? Etc.


I think Steve nailed it; the cost of duplicating a complex log antenna might not be worth it. But, anyone contemplating a homebrew
design might consider using wire elements instead of aluminum tubing. Think "Titanex":

http://www.mydarc.de/dl6ip/Log-Periodic-Ant.html

That would cut the costs considerably, and is the approach I'd take.

Pete

NH7RO
01-02-2012, 05:14 AM
I agree about hard to see the hub and dual boom of the Titanex but the beam looks great, doesn't it?

I would opt for a 20-10 or 20-6M scaled down version if I decided on this route (I'm not on 40M much and not on 30m at all). It might also be all the more doable as a 17M-6M design, too.

One question for Ben; Do you know what size fiberglass that smaller Cubex aluminum spider accepts? Their website doesn't mention it as far as I can see. If MaxGain Type 1 spreaders fit that spider, well, Bob's your uncle!

I do believe Mac's Sporting Line is 350lb test so it should be fine; it's what I'd use. While the 18 ga. wire I mentioned works fine and seems to hold up I might want to find some 16 or even 14 ga. bare copper since the 18 ga. stranded tends to snarl up/kink at the slightest opportunity.

73, Jeff

AE7F
01-02-2012, 07:56 AM
I agree about hard to see the hub and dual boom of the Titanex but the beam looks great, doesn't it?

One question for Ben; Do you know what size fiberglass that smaller Cubex aluminum spider accepts? Their website doesn't mention it as far as I can see. If MaxGain Type 1 spreaders fit that spider, well, Bob's your uncle!

73, Jeff

Not sure yet on the size that the Cubex hub supports. I will find out though.

...

After playing significantly with this calculator (http://www.arcticpeak.com/antennapages/LPDA.htm) and using values from this dBi estimator chart (http://glendash.com/Dash_of_EMC/Log_Periodic/Log_Periodic.htm), I can't figure out how some manufacturers are making such high dBd claims.

I used a Tau of 0.9 and a Sigma of 0.06, which (according to the gain predictor chart) will only yield around 6.7dBi of gain, yet the LP calculator calculates a boom length of 9.687m, or around 31ft. Subtract around 2.1dBi to get gain in dBd and we are left with around 4.6dBd for a log periodic with a 31ft boom.

How is Tennadyne getting 5.1dBd from a 12ft boom? Is it because of the dual boom design?

AC0H
01-02-2012, 03:45 PM
How is Tennadyne getting 5.1dBd from a 12ft boom? Is it because of the dual boom design?

They aren't.
Short boom logs have about the same forward gain and F/B potential (notice the word potential) as a 2 element Yagi-Uda design.
A 31ft Log with the right number of elements will have the gain and F/B of an optimized 18-24' three element Yagi (on 20m).

Yagi's are narrow band antennas. Logs are broadband. There is a price to be paid for being broadband, namely forward gain and F/B/R compared to Yagi's.

The SteppIR antennas have taken that truism and thrown it on it's ear with their tunable antennas.
There is NO free lunch. SteppIR's are broadband because they tune the length of the elements for each 75 KHz section of each band.
The price (not just $$$) to be paid there is complexity and serviceability.
When the motors on your SteppIR die or the control cable gets cut or nicked, or the driver chips in your controller get blown up by static charge, or the Beryllium/Copper elements in the beam break or get piled up in a tube......your done.

Hope you don't have to climb very far or often to fix it.

Quit comparing gain figures between Yagi's and Logs. They're apples and oranges.

AE7F
01-02-2012, 04:36 PM
Thanks for the reply.

I was aware of how Steppir was tuning their elements and so forth. I guess I'm still not clear on the difference between the T6 and what I'm trying to build, unless the T6 is supposed to be a yagi design or as you mentioned, is only claiming gain potential. Even the Titanex DLP-11 is claiming 5.1dBd out of a 19ft boom.

I wonder if there are different versions of the Tau/Sigma gain prediction chart that people are using.

Bottom line is I want to come up with a design on a shorter than 31ft boom for 5 bands that I can expect to have 5+dBd of gain - just like is claimed by the T6 or DLP-11.




They aren't.
Short boom logs have about the same forward gain and F/B potential (notice the word potential) as a 2 element Yagi-Uda design.
A 31ft Log with the right number of elements will have the gain and F/B of an optimized 18-24' three element Yagi (on 20m).

Yagi's are narrow band antennas. Logs are broadband. There is a price to be paid for being broadband, namely forward gain and F/B/R compared to Yagi's.

The SteppIR antennas have taken that truism and thrown it on it's ear with their tunable antennas.
There is NO free lunch. SteppIR's are broadband because they tune the length of the elements for each 75 KHz section of each band.
The price (not just $$$) to be paid there is complexity and serviceability.
When the motors on your SteppIR die or the control cable gets cut or nicked, or the driver chips in your controller get blown up by static charge, or the Beryllium/Copper elements in the beam break or get piled up in a tube......your done.

Hope you don't have to climb very far or often to fix it.

Quit comparing gain figures between Yagi's and Logs. They're apples and oranges.

AC0H
01-02-2012, 07:22 PM
Thanks for the reply.

I was aware of how Steppir was tuning their elements and so forth. I guess I'm still not clear on the difference between the T6 and what I'm trying to build, unless the T6 is supposed to be a yagi design or as you mentioned, is only claiming gain potential. Even the Titanex DLP-11 is claiming 5.1dBd out of a 19ft boom.

I wonder if there are different versions of the Tau/Sigma gain prediction chart that people are using.

Bottom line is I want to come up with a design on a shorter than 31ft boom for 5 bands that I can expect to have 5+dBd of gain - just like is claimed by the T6 or DLP-11.

Then run through the design software with specs for an Tennadyne T6 and leave the gain blank.
Specify the Tau/Sigma, number of elements and boom length then let the software solve for gain.
The software may not let you do that.

Getting 5dBd from a 12' boom, 6 element log periodic antenna is akin to bending the laws space/time.
I might believe 3 to 3.5 but not 5.
Also, were these gain figures quoted over real ground or free space?

AC0H
01-02-2012, 07:29 PM
I just ran the T6 through LPCad30 that came with my antenna book.

6 elements, 12 foot boom, 1 inch diameter elements.
Gain came back as 3.85 dBd or 6dBi, front to back varied from 8 to 15 dB
About the same as a 2 element yagi.

AE7F
01-02-2012, 10:17 PM
Thanks. I am going to have to go along with that because all of the calculations I was doing last night just weren't making sense when looking at figures quoted by other antenna manufacturers. Now I don't feel so bad about a 30ft boom!


I just ran the T6 through LPCad30 that came with my antenna book.

6 elements, 12 foot boom, 1 inch diameter elements.
Gain came back as 3.85 dBd or 6dBi, front to back varied from 8 to 15 dB
About the same as a 2 element yagi.

AE7F
01-02-2012, 10:21 PM
I think you hit the nail on the head here. Calculations just weren't adding up when I was doing them.


Then run through the design software with specs for an Tennadyne T6 and leave the gain blank.
Specify the Tau/Sigma, number of elements and boom length then let the software solve for gain.
The software may not let you do that.

Getting 5dBd from a 12' boom, 6 element log periodic antenna is akin to bending the laws space/time.
I might believe 3 to 3.5 but not 5.
Also, were these gain figures quoted over real ground or free space?

AE7F
01-03-2012, 12:55 AM
Went back to http://www.arcticpeak.com/antennapages/LPDA.htm and entered 0.89 for Tau and 0.06 for Sigma and a low frequency of 14.000. The gain calculator at http://glendash.com/Dash_of_EMC/Log_Periodic/Log_Periodic.htm predicts a respectable 4.3ish dBd. This is at the cost of a 30.3ft boom. I think at least several of us agree that this should be a real world prediction. However, the calculator says the last element provides a maximum usable frequency of 35mhz. So if I leave off Ln+11 (the 12th element), the MUF becomes 31.326 and the boom now can be shortened to 27.7ft. So we have a log periodic that can cover 14-31.326mhz with good gain from a boom of around 28ft.

I do have further questions:
0. Should I input a low frequency value of slightly less than 14.000 so that the antenna will work properly in the CW DX portion of 20 meters?
1. The calculator I mentioned provides "length of shorting stub" of 8.78ft. What do you do with this stub? That's a lot of wire to hang around.
2. What would I use for feed line and how do you connect it to the elements? Most designs call for 180 degree shift, so would you need to just run 2 parallel wires and shift them per element accordingly? Is there any other kind of special feed line for this purpose?
3. How do you route the feed line? Up the tower and mast and on the underside of the fiberglass boom to the feed point?
4. What type of balun and what ratio? How do I determine this?
5. What are the implications of pinning or placing bolts or pins through fiberglass? I would need to figure out a way clamp perpendicular poles - fiber to fiber or fiber to metal, etc.
6. Any problems using a metallic center post?

AE7F
01-03-2012, 08:11 PM
So do you guys think this type of framework would work? I would still have to connect the framework to the rotor mast. Depending on the balance point, this might need to be somewhere around segment C or D.

82543

NH7RO
01-03-2012, 09:28 PM
Ben; Section C worries me in that it is narrower than Section B & D---I wonder if it would hold up to whatever weight/stress it is subjected to?

My hunch is that you'd be safe with a larger diameter tube starting with D and working your way down to the thinnest for tube A as you go out. I realize that this will likely cost you extra but might make the difference in staying up in the air or not.

Also, what is that 10' section of PVC doing? Mayber that's a typo and you mean 10"? I wouldn't use 10' of PVC anywhere (too flimsy and too heavy)---even a cut down 15' cheap FG fishing pole would be far better.

Otherwise I'd say that your design looks good to go and that the balance point might be somewhere along Section D, FWIW.

73, Jeff

AE7F
01-04-2012, 10:37 PM
Good morning Ben; I think your wire cost could be a lot less than 27 cents/foot (also I think you wrote .027 when you meant $0.27) if you went with Home Depot 18 ga. stranded bare copper. This is what I've used for a couple of my Moxons and it works out to around 5 to 6 cents/foot (250' spool for $12.66 last time I priced it). Two spools for about $26 and you'd have a bit left over.


This must be what you are talking about:
http://www.homedepot.com/Electrical/h_d1/N-5yc1vZarcd/R-202206412/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053



For rope I use a thin cammo colored dacron called Mac's Sporting Line (Google and it'll turn up) that comes in 100' spools and is available here at True Value Hardware for $9 a spool (but is a lot cheaper online). It is probably about 1/16", nearly invisible and tough as...dacron. Use it for antenna rope, guy lines for lightweight antennas, etc.


I didn't find the Mac's stuff yet but I saw a lot of other stuff. It looks like the use of Kevlar is accepted for guying the spreaders and general purpose rope can be used for the wire element support (both with dacron coating of course).

AE7F
01-04-2012, 10:46 PM
A lot of thought and effort has gone into this by now by many people. Thanks everyone for your help and replies.

This design is definitely doable and depending on how you do it, I think would price at around $400 or less. This is just a guess. This is a bit more than I intended. Also the design has some issues, especially when trying to come up with a 30ft+ span of fiberglass. Gain and aesthetics would be nice.

So... I started looking back at the Spiderbeam design and have put some thought into doing a home brew version of it as well. Both this and the Spiderbeam are very similar and compare in most ways. The advantage to looking at the Spiderbeam as my first DIY beam is that there is more information on the design and many have been built and tested already.

I will come back to this design but for now I will temporarily give it a rest and thank everyone for their contributions.

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