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KJ4NBM
07-01-2009, 04:32 PM
I put up a end fed wire a few months ago for general listening on SW and HF ham bands. Now that I have my license I'm transmitting on it with limited results.
Its about 85' long; run from the house out to an oak tree out back. Its only 8 to 12 ft off the ground. Its fed with coax to keep RF out of the house, so I know there's a major impedance mismatch there. I can tune it on most HF bands except 75-80M with my MFJ tuner.

Anyway here are my questions:

1. Will installing a 9:1 balun between the coax and wire be beneficial for transmitting?

2. Will raising the height of the antenna make any difference in its performance?

3. Should the coax shield be grounded at the feedpoint (without balun)?

73's, KJ4NBM Matt

KA4DPO
07-01-2009, 04:56 PM
I put up a end fed wire a few months ago for general listening on SW and HF ham bands. Now that I have my license I'm transmitting on it with limited results.
Its about 85' long; run from the house out to an oak tree out back. Its only 8 to 12 ft off the ground. Its fed with coax to keep RF out of the house, so I know there's a major impedance mismatch there. I can tune it on most HF bands except 75-80M with my MFJ tuner.

Anyway here are my questions:

1. Will installing a 9:1 balun between the coax and wire be beneficial for transmitting?

No, that would simply increase the losses.

2. Will raising the height of the antenna make any difference in its performance?

Yes, higher is better.

3. Should the coax shield be grounded at the feedpoint (without balun)?

Don't bother, see below.....

73's, KJ4NBM Matt

The best way to feed a random wire is to bring the wire directly to the tuner. Using coax is not helping you in the least and the shield is probably causing more harm than good.

The rules for a random wire are: You must have a very good RF ground. You need to have several counterpoise wires either on or just under the surface of the ground. More is always better since it increases ground conductivity.

Get the wire up higher if you can. It doesn't have to be horizontal but can slope from a window or roof sill up to a higher point but higher is always better for a random wire.

Use a good wide range tuner, not some little junky thing. An L network tuner that will handle more than the legal limit can be made for very little money. One that will take care of your needs at 100 watts can be built on a piece of plywood in less than an hour and will work as well or better than many commercially made tuners.

If you have a decent tuner run the wire to the single wire connector on the back, do not use coax.

If you are an ARRL member go here and read the two articles on random wire antennas and matching networks.

http://www.arrl.org/members-only/qqnsearch.html?search=1&words=random+wire+antenna&name=&call=&year=&month=&selpub%5B%5D=QST

WB2WIK
07-01-2009, 04:57 PM
>KJ4NBM;1624037]I put up a end fed wire a few months ago for general listening on SW and HF ham bands. Now that I have my license I'm transmitting on it with limited results.
Its about 85' long; run from the house out to an oak tree out back. Its only 8 to 12 ft off the ground. Its fed with coax to keep RF out of the house, so I know there's a major impedance mismatch there. I can tune it on most HF bands except 75-80M with my MFJ tuner.

Anyway here are my questions:

1. Will installing a 9:1 balun between the coax and wire be beneficial for transmitting?<

::Probably not. The impedance of an 85' end-fed wire varies all over the place with frequency, from low to high.


>2. Will raising the height of the antenna make any difference in its performance?<

::Yes, absolutely. The same wire at 50' above ground will dramatically outperform what you have.

>3. Should the coax shield be grounded at the feedpoint (without balun)?<

::You'd be far better off without the coax at all, it's doing you no good and will not effectively keep "RF out of the house." Much better would be to eliminate the coax completely, bring the wire all the way to the house (like the ham shack window or windowsill area), and put the MFJ tuner in the window with the wire connected to its "single wire" terminal and a VERY good earth ground on the chassis of the tuner. If you have a first story ham shack and can sit the tuner in a window, the "ground wire" can be only a few feet long, from the windowsill down to earth immediately below -- that's not a bad ground. Use very heavy copper or aluminum wire and an 8' copperclad ground rod driven into undisturbed soil so 7'6" is below ground.

That's not a "good" earth ground, but it's a start. You can make it better by adding copper wire ground radials to the rod, fanning them out like spokes of a wheel, all about 20'-30' long (just laying on the ground is fine, or very slightly beneath the soil is fine, too).

This will blow the doors off what you have now.

WB2WIK/6

KB3RHV
07-01-2009, 05:02 PM
You want to get it up about 35 ft or higher if you can.

You will also want to use a unun and not a balun since your feed is unbalanced and the antenna is unbalanced.

http://www.balundesigns.com/servlet/the-Ununs/Categories

I would also run a few ground level counterpoise wires that are cut to 1/4 wave of the lowest band that you are going to use. You can also add a ground rod connected to the unun and run the counterpoise wires from that as well.

73

WJ5O
07-01-2009, 05:12 PM
Matt,
I took a satellite look at your location....with the number of trees in your yard it would be easy to hang a fan dipole which will out perform a tuned random wire for transmitting. :)

WA7KKP
07-01-2009, 06:55 PM
I put up a end fed wire a few months ago for general listening on SW and HF ham bands. Now that I have my license I'm transmitting on it with limited results. [edited]

Anyway here are my questions:

1. Will installing a 9:1 balun between the coax and wire be beneficial for transmitting?

2. Will raising the height of the antenna make any difference in its performance?

3. Should the coax shield be grounded at the feedpoint (without balun)?

73's, KJ4NBM Matt

Answer to #1 --- not really. The nice thing about random longwires is that they are pretty much a no-brainer type antenna . . . as long as you have a good grade WIDE RANGE antenna tuner, which can be as simple as a coil and capacitor in the venerable L-network. Coil in series, and the capacitor across either the input or output of the coil depending on where the wire impedance lay -- high or low.

Answer to #2 --- it might, it might not. I've had great luck with random wires just over my head. What seems to matter is a good ground or counterpoise system which (in application) is the other 'half' of your antenna. If it appears to work well, leave it alone. If it doesn't work as well as you want, then experiment with different lengths, and heights if necessary. I've discovered that in this application, the more WIRE you have the better off you should be.

Answer to #3 --- Coax should NOT be used in a tuned line situation as in your example. Remove it and just run the wire into the shack and to the single wire terminal on your tuner. The reason -- depending on frequency, the voltage/current peaks can break down the dielectric (voltage) or cause hot spots (current) that will damage the coax. This is the reason that open wire feedline (ladder line) is used -- higher breakdown voltage and current capacity than low impedance coax lines.

I've used random wires for years, and home-brewed an L-Match antenna tuner using the roller coil from a BC-191/375 transmitter and a 200 pf variable, built into the chassis of a TU tuning drawer. Eventually i'll put in an SWR bridge, as I have room to burn inside. This is my KISS tuner, and with SO-239''s I can also tune coax lines to a perfect match for my solid-state rigs.

Have fun experimenting -- I have . . .

Gary WA7KKP

WB2WIK
07-01-2009, 09:07 PM
Answer to #3 --- Coax should NOT be used in a tuned line situation as in your example. Remove it and just run the wire into the shack and to the single wire terminal on your tuner. The reason -- depending on frequency, the voltage/current peaks can break down the dielectric (voltage) or cause hot spots (current) that will damage the coax. This is the reason that open wire feedline (ladder line) is used -- higher breakdown voltage and current capacity than low impedance coax lines.



::There's other reasons. On frequencies where the end fed wire represents a very high impedance, the shunt capacitance of coax (at about 26 pF/foot for 50 Ohm cable) literally "shorts out" the antenna, rendering it useless in many cases (depending on coax length and frequency). Also, when terminated in a big mismatch as it will often be, coax cable loss skyrockets and can be 10 dB or more in many cases (again, depending on coax length and mismatch). Both these factors are major reasons to not use coax for this application.

KJ4NBM
07-01-2009, 11:15 PM
Matt,
I took a satellite look at your location....with the number of trees in your yard it would be easy to hang a fan dipole which will out perform a tuned random wire for transmitting. :)


Well, there are two big trees that are probably aren't on that satellite pic anymore; a big pine in the back and a maple in the front yard. Both were dead or dying when I bought the place so I had em' cut out in case of a hurricane.
Anyway, what exactly is a fan dipole:confused:

KA4DPO
07-01-2009, 11:40 PM
Well, there are two big trees that are probably aren't on that satellite pic anymore; a big pine in the back and a maple in the front yard. Both were dead or dying when I bought the place so I had em' cut out in case of a hurricane.
Anyway, what exactly is a fan dipole:confused:


Go here.....

http://www.hamuniverse.com/multidipole.html

WB2WIK
07-02-2009, 12:09 AM
Anyway, what exactly is a fan dipole:confused:


::I'm a big fan of dipoles. That's what it means.:p

What most of us call a fan dipole is really just a parallel dipole, which is multiple dipoles cut for different frequencies but sharing a common feedpoint.

I call it a Fanned Eyepole, just because that's cute.:)

W5DXP
07-02-2009, 12:43 PM
3. Should the coax shield be grounded at the feedpoint (without balun)?

Where are you going to find a ground at the feedpoint?

KJ4NBM
07-02-2009, 02:10 PM
::I'm a big fan of dipoles. That's what it means.:p

What most of us call a fan dipole is really just a parallel dipole, which is multiple dipoles cut for different frequencies but sharing a common feedpoint.

I call it a Fanned Eyepole, just because that's cute.:)


Ah, ok. Yeah I'm planning on making a triband parallel dipole for 20, 17, and 10 meters. I'm going to try an attic installation with it. The wife isn't to happy about alot of wires running high across the yard

KR2D
07-02-2009, 02:36 PM
The wife isn't to happy about alot of wires running high across the yard

Wires 30 feet up are invisible. We're talking 14 guage here, not the fat cables used for power, phone and CATV. Nobody sees them unless they get a coating of ice/snow in the winter. And very few people ever look up anyway. Put them up when she's not home and see how long it takes for her to notice them. My doublet was up for weeks before my wife asked where my antenna was and I had to point it out to her. Not that she cares about how it looks, she was just curious.

KJ4NBM
07-02-2009, 03:36 PM
Hmm, good point about the wire. My random wire is 16 gauge so it is REALLY hard to see:) I've never tried an attic antenna so thought I'd experiment with it. It will be easy to hang up there and no weatherproofing to worry about. Not sure about TVI and electrical noise issues though. If it doesn't work I'll just relocate it outside.

WB2WIK
07-02-2009, 04:59 PM
Ah, ok. Yeah I'm planning on making a triband parallel dipole for 20, 17, and 10 meters. I'm going to try an attic installation with it. The wife isn't to happy about alot of wires running high across the yard

::An outdoor installation is usually less work, and also works better. If you make the wires really high, nobody will be able to see them.

Black jacketed coax fades into backgrounds pretty well, but some coax is available in other colors, too. "Marine grade" coax is usually white. A few manufacturers of RG8X "mini-8" make it in black, white, gray, blue, possibly other colors. It's easy to "hide" outdoor antennas if you can get them high enough.

WB2WIK/6

AE5JU
07-08-2009, 03:44 PM
Go here.....

http://www.hamuniverse.com/multidipole.html


Here's the sequel to that dipole article:

http://www.hamuniverse.com/ae5jumultibanddipole.html

And here's an improved dipole center section:

http://forums.qrz.com/attachment.php?attachmentid=28288&stc=1&d=1247067331

http://forums.qrz.com/attachment.php?attachmentid=28289&stc=1&d=1247067357

This is a Jetstream Dipole Insulator (JTCE1) bolted to a piece of plastic kitchen cutting board. This material is less brittle in cold weather.

The V-cut in the bottom is to allow easier wrapping of the connector with coax seal. The Jetstream Dipole Insulator is available in various colors and will have different suffixs, JTCE1B for blue, JTCE1BK for black, JTCE1W for white, JTCE1G for gray, JTCE1GN for green. About $15 USD. I got mine from www.jandl.com (http://www.jandl.com) (J and L).

http://forums.qrz.com/attachment.php?attachmentid=28290&stc=1&d=1247067377

And another way to make a choke balun:

http://forums.qrz.com/attachment.php?attachmentid=28291&stc=1&d=1247067483

Attach 5 ferrite snap on beads right up next to feedpoint end. I got these from Palomar Engineers, # FSB-1/4 to fit Mini-8 (RG-8X) coax.

WA5WRD
08-25-2010, 06:33 PM
I put up a end fed wire a few months ago for general listening on SW and HF ham bands. Now that I have my license I'm transmitting on it with limited results.
Its about 85' long; run from the house out to an oak tree out back. Its only 8 to 12 ft off the ground. Its fed with coax to keep RF out of the house, so I know there's a major impedance mismatch there. I can tune it on most HF bands except 75-80M with my MFJ tuner.

Anyway here are my questions:

1. Will installing a 9:1 balun between the coax and wire be beneficial for transmitting? Probably not! You still have to hook it to either ground or modify it. You still do not have a return.

2. Will raising the height of the antenna make any difference in its performance? YES,YES,YES! But the lower antenna might be what you want as an Amateur.
The lower the antenna the higher the angle of radiation.
Higher radiation angle means you are exciting the Ionosphere and just might get around the world. Not so much on the lower bands, "160-80" but 40M up is good.
So if you want local contacts on 80M you need to be up about 1/4 wave length, "about 66Ft."
A good vertical on 80M is great for local contacts.

3. Should the coax shield be grounded at the feedpoint (without balun)? Absolutely!

73's, KJ4NBM Matt

I see three problems!
Problem #1. Without the shield attached to either ground or feeding the antenna as a split, "dipole or Windom" there is no rf return path for the RF.
Problem #1 if you feed a long wire from the end and you have any multiple of a 1/2 wave length you will have problems loading it. Even with a tuner.
I have a MFJ-941E and I've had the same problem.
I did however remember there are some problem lengths and looked it up.
I now have a 203ft long "long wire." Works great on all bands "160 through 10M."
The published safe lengths for avoidance of the multiple 1/2 wavelengths for 160 through 10M, in ft is:
29,35,41,58,71,84,107,119,148,203,247,407,423
Your, "about 85ft" is between the good lengths of "84 and 107ft." there are several lengths between the two that simply sux.

I also noted you said your wire is "ABOUT 85ft." That's not good enough.
Is it 85ft or not? That's the question.
Random is really not a good idea. You should know what you're dealing with.

If I were you, I would either cut it to exactly 71 or 84 or exactly 104 ft. and forget the coax. If your antenna is working you will absolutely have RF in the house unless you live in a FARADAY CAGE so what's the point?
Also with the coax open on the end you are attempting to load essentially a long center conductor with the shield, "ABOUT 85ft" shorter than the center conductor.
Some calculations could be done on this but why waste the time?
Since the coax is open your probably getting more radiation into your house from unbalanced currents on that coax than a piece of wire would cause.
To try it as a single wire without much modification. Make yourself a very short RG8M cable with a PL-259 connector and connect it to your existing cable via an adapter.
Get a cheap adapter at Radio Shack. Cheap as in money, we all know Radio Shack junk is cheap in quality.
Now, on the open end of the short RG8-M pig tale you just made, "short the shield and center conductor together, connect it to your tuner and strap the tuner as per instructions for a wire and ground it properly. You should have it grounded anyway for your radio's safety and yours.

Try it, you might get away with it.
Especially if your, "about 85ft" wire happens to be close to 84 or 107 ft..

There are already known "good"working designs to use the wire you already have with very little modifications and do it quite efficiently. First thing, make it the right length. Measure it with a tape measure, "ABOUT Xft" isn't good enough!

If you just insist on feeding it with a coax then, "using your wire", measure from the feed end and cut it to exactly 8.1 meters, "or 26.5781ft" and put in an insulator and a 50Ohm to 300Ohm balun.
Then measure the rest of the wire and at the far end make sure it is exactly, "32.9 Meters, or "107.953125ft." The over all length should be exactly, "41.0 Meters" or "134.53125ft."
You will now be able to tune it mostly without a tuner at all.
You have just built a very good antenna!
It's called a, "WINDOM ANTENNA." It's been around a very long time and works great!

AI3V
08-25-2010, 07:19 PM
One of the problems the new station faces when putting his or her first transmitter on the air, is he dosn't have any frame of reference.

Erecting a "Random Wire" , without a groundplane -The "other Half" of the antenna- and expecting this to work on all bands with some magic auto tuner is just about the VERY WORST POSSIBLE antenna you could start out with.

My standard recomendation,

Build and install a SINGLE BAND, COAX FED DIPOLE for a reliable band.

That would be 40 meters, because, 40 meters is allways open to somewhere.:):cool:

If you have some $$ burning a hole in your pocket, use a balun.

If the balun makes a difference, you need to get the antenna higher up, and farther away from everything. :eek:

After a while, when you have a hundred or so contacts in the log, then try a different skyhook.

Rege

KB4QAA
08-25-2010, 10:43 PM
.."published safe lengths" for a random long wire...

BWahahahahahahahaha No. :D

KB4QAA
08-25-2010, 11:36 PM
ARRL Antenna Book, 20th ed.

Long Wire Antennas:
"..The construction of long wire antennas is simple both electrically and mechanically, and there are no especially critical dimensions or adjustments." 13-1

Calculated Length:
"There is nothing very critical about wire lengths..... There is no need to try to establish exact resonance at a particular frequency for proper antenna operation." 13-5

K4EEZ
08-26-2010, 03:05 PM
GEEZ come on guys 85 Ft???

make the random wire into an off center dipole look at the Bux OCD wire dipole for EG... just an idea...
__________________________________________________ _______



I put up a end fed wire a few months ago for general listening on SW and HF ham bands. Now that I have my license I'm transmitting on it with limited results.
Its about 85' long; run from the house out to an oak tree out back. Its only 8 to 12 ft off the ground. Its fed with coax to keep RF out of the house, so I know there's a major impedance mismatch there. I can tune it on most HF bands except 75-80M with my MFJ tuner.

Anyway here are my questions:

1. Will installing a 9:1 balun between the coax and wire be beneficial for transmitting?

2. Will raising the height of the antenna make any difference in its performance?

3. Should the coax shield be grounded at the feedpoint (without balun)?

73's, KJ4NBM Matt

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