PDA

View Full Version : 3-element beam / Yagi for 10 meters: What can I expect?



AE7F
10-16-2011, 05:47 AM
I was just given a 3 element beam antenna. Some simple estimated measurements (~16+ ft elements) lead me to believe it is a 10 meter antenna. It does not have any traps or coils.

It has a gamma match but I might have to work with/repair that. Is there a good source of information on gamma match specs for a 10 meter 3 element beam? If there is, I can make sure I'm in the ballpark. I take it that if you don't use one, you'd have to settle with the impedance mismatch or you'd have to trim the antenna, right?

If any of you have used a 10 meter, 3 element beam before, what were your results? Have you used one recently when the band was open? What type of gain can be expected, 7 or 8db over a dipole?

I have a G5RV, which is not a great antenna for 10 meters, but I have made some fun DX contacts. I also have a vertical CB antenna that I messed around with on 10 meters and had fun talking to Asian stations.

I'm just experimenting right now and everything is temporary. My G5RV is in an inverted V configuration right now with the apex at a measly 25ft. The small vertical is at 6ft above ground. The best I could do right now with the 3 element beam would be about 20ft above ground.

If I get this 10 meter 3 element beam working right, what difference if any could I expect over the G5RV or the small vertical?

AE7F
10-16-2011, 06:03 AM
I did find this thread:
http://forums.qrz.com/showthread.php?34839-Ballparking-a-gamma-match

W9GB
10-16-2011, 03:24 PM
I was just given a 3 element beam antenna.
Some simple estimated measurements (~16+ ft elements) lead me to believe it is a 10 meter antenna.
It does not have any traps or coils.

Yes, this sounds like a MONO-Band, 10-meter yagi. Get a tape measure and measure the boom's length and tubing OD.
IF you could attach some photos of this antenna's feedpoint or boom/element attachments --
then we may be able to idenitfy the manufacturer for you.

There were also some 11/10-meter 3-element beams made in 1960s/1970s (such as the Maco 103C, 11.5 feet boom length) --
http://www.macoantennas.net/AntennaDetailedPages/M103.html

You adjusted the polarization, element length and/or matching system for optimal usage (desired operating frequency)
as outlined in the M103C manual.
http://www.macoantennas.net/files/M103C_2011.pdf

w9gb

W9GB
10-16-2011, 03:26 PM
I was just given a 3 element beam antenna.
Some simple estimated measurements (~16+ ft elements) lead me to believe it is a 10 meter antenna.
It does not have any traps or coils.

The Cushcraft 10-3CD Skywalker is their 10-meter, 3-element (mono-band) beam
http://www.cushcraftamateur.com/pdffiles/951349.pdf


If I get this 10 meter 3 element beam working right, what difference if any could I expect over the G5RV or the small vertical?

IF you enjoy the DX hunts on 10 meters, when the solar conditions are good,
you should be pleased with the directional performance -- compared to an omni-directional vertical.

w9gb

KM1H
10-16-2011, 04:05 PM
Performance will be poor to excellent depending on how carefully it is assembled/tuned, height mounted, topography, and propagation. Considerable ground gain is possible which ads to the basic yagi gain.

Carl

K7MH
10-16-2011, 04:06 PM
what difference if any could I expect over the G5RV or the small vertical?

If set up right at a decent height, It is like the difference between driving an old Datsun B210 and a new Camaro.

It would be a huge improvement on 10 meters.
Much better signal strengths.
You don't notice the QSB nearly as much due to higher signal strengths.
Much better signal from you to the DX.
Can carry on a QSO far longer.
It's directive.
Less noise when horizontal.
...looks cooler!;)
There is really no comparison.

AE7F
10-16-2011, 04:39 PM
When inspecting / reassembling / etc., what do I need to do at the joint sections (cleaning, etc)? I'll post pics later today...

KM1H
10-16-2011, 04:49 PM
I always sand the element part that slides into a bigger section and use a wire brush for its inside. Then lightly coat with electricians aluminum wire antioxidant. Use all stainless hose clamps, not ones with regular steel wormscrews.

Carl

K8JD
10-16-2011, 09:06 PM
I bought my HyGain 103 10M Yagi when I bought my brand new TS520 so that dates it.
I had to replace the rusty hose clamps the elements were assembled with when I moved to this QTH, 22 years ago, I did the steel wool cleaning when I put it back together .
I had been using an 8 ft GP vertical at 20 ft and the new Yagi was night and day difference. I rarely got into Europe or Asia with the GP and the Yagi got me DX like I could not believe !
I wkd islands in the Pacific that I had to go over my old National Geographics maps for hours to find !


I always sand the element part that slides into a bigger section and use a wire brush for its inside. Then lightly coat with electricians aluminum wire antioxidant. Use all stainless hose clamps, not ones with regular steel wormscrews.

Carl

WB2WIK
10-16-2011, 09:13 PM
NoAlOx or similar is a good anti-oxidant. I use "ScotchBrite" polishing cloths to buff up the aluminum interfaces, then apply NoAlOx, which can be found at many hardware stores and virtually all electrical supply houses. It's cheap. ScotchBrite cloths are in most grocery stores and lots of places.

Don't use steel wool.

A gamma match is essential for designs where the center of the driven element is grounded to the boom, and that's the reason beams use gamma matches. If the element is insulated, you can use other stuff. Hy-Gain doesn't use a gamma, they use a "beta" match with an insulated driven element.

They both work.

The gamma tunes out element reactance but it won't change radiation resistance, so the element has to be the right length to begin with. 16' elements indeed sounds like a 10m monobander.

Compared to a G5RV on 10m (and a G5RV is truly a terrible antenna on 10m), this will be like going from a stepladder to a crane. You're going to be very surprised how much better it is.

AE7F
10-16-2011, 10:55 PM
Dimensions: (pics later)
boom: 12' (144")
reflector: 17'6" (210")
driver: 16'7" (199")
director: 15'9" (189")
gamma: outer rod - 2'1" (25"), outer rod plus inner rod as it is currently adjusted - 2'4" (28")

What kind of specs could we estimate based on these dimensions?

W9GB
10-16-2011, 11:45 PM
What kind of specs could we estimate based on these dimensions?
YES, it is a 3-element, 10-meter antenna. We have already deduced this.
The element lengths are adjusted depending WHERE you desire the SWR dip between 28 - 30 MHz

Driver: 16'7" (199")
Boom length: 12 feet

Those dimensions are correct for a Cushcraft 10-3CD tuned around: 28.350 to 29.250 MHz

NEXT, The ASSEMBLY method of the antenna can often IDENTIFY the manufacturer !

Cushcraft likes to Slot (cut) the aluminum tubing and use SS hose clamps.
Maco likes to Swag aluminum tubing and telescope the tubes.

===
LOOKING at the antenna's BOOM section.

Maco M103C uses TWO pieces of aluminum tubing.
BOTH pieces are is 1-1/2 inch OD, 6 feet in length, ONE piece is swagged for a telescoping fit.
Mast / Boom clamp hold the overall boom together, then to mast.
Overall boom LENGTH is 11 feet and 7 inches.

Cushcraft 10-3CD uses THREE piece of aluminum tubing.
TWO pieces are 1-1/2" OD; One is 6 feet in length, Other is 4 feet in length.
The THIRD and CENTER Piece is 1-5/8" OD and both ends of this piece are slotted for hose clamp assembly.
Mast / Boom clamp holds this third/center tubing section to mast.
Overall boom LENGTH is 12 Feet.

==
w9gb

AE7F
10-17-2011, 12:02 AM
Sorry. I already agreed on the 10m design. I should have been more specific. I was wondering what the gain and f/b ratio/etc. specs were. There are no slots cut. The pieces fit into each other. Thanks for the replies.

W9GB
10-17-2011, 12:19 AM
Photos would be faster (photos say a thousand words, you can not describe), since you are describing small pieces.
I did say to get that tape measure --

1. How many pieces of tubing used for this Boom? Are they all the same OD ? What is the OD of boom (inches) ?
2. How are the 3 elements attached to boom? Holes drilled in elements and then U-bolt clamped to boom?

w9gb

WB2WIK
10-17-2011, 01:20 AM
Should have about the same characteristics as any 12' long 10m beam.

Knowing the gain and F/B ratio won't make it work any differently. If you want, you could plug everything into EZNEC, including installation height above earth, and get some real numbers that are better than estimates.

KM3F
10-17-2011, 03:38 AM
F/B has little value under most operating conditions.
A 3 element pattern is very broad out front so absolute direction control is of little importance.
Forward gain figures are the higher the better for the long distance weak signals you want to work.
On 10m, the antenna height should be at least 40 feet or the pattern angle suffers for long distance work when your splitting hairs for signals.
However, with the sunspot activity increaseing the height becomes less important than it would be under lesser conditions such as ES propagation and tropo.
Good luck.

KA9VQF
10-17-2011, 03:54 AM
I have an old Archer Crossbow III beam leftover from my bad nasty CB days. It only took a little retuning to make it into a decent 10M beam.

When I used it with my CB I had it mounted on the mast in the vertical position. Now that I’m using it with my ham radio I have it horizontal.

Its only up around 25 feet and I turn it by reaching out the window and using my hand so you might say I have an Armstrong rotor.

AE7F
10-17-2011, 05:44 PM
...I turn it by reaching out the window and using my hand so you might say I have an Armstrong rotor.

hahahahaha.... okay, well that's new to me. Thanks for that.

I hope to try out this beam today. It is up at 10ft right now but that's just until I get a new cable connected.

I am working on a tower solution but right now about the best I could do with this beam would be 20 feet. There might come a time soon when I can go to 35' but winter is coming fast and if I can put anything somewhat affordable at 35', it might be a hex.

AE7F
10-18-2011, 02:59 AM
Well, the great news is that it works. In just a few minutes I worked Finland, China, and Russia. Also worked T32C on 10m SSB. Bad news is now I have to figure out how to put up another mast. These contacts were made with the beam at 20ft.

AE7F
10-24-2011, 04:49 AM
China, South Korea, Taiwan, Japan, etc. Can you guess which direction the beam is pointing?

Really fun to get a beam in time for 10m openings.

Another bonus is that the XYL thinks the 10m beam is a nicer looking antenna than my inverted V. Cool. (visions of Steppir running through my head....) :p

W9CAC
10-24-2011, 02:49 PM
Most gamma matches are made from an inner section of coax with a piece of aluminum tubing slid over it to adjust for the SWR. Borrow or buy an antenna analyzer for this job. I have built a 2 meter and a 6 meter yagi with gamma matches. They were both a bit fiddly to tune, but with a analyzer, you will be able to do it in a rather short period of time. A preliminary tune to around 1.5-1 at eight to ten feet off the ground maybe all you need. I mount mine onto similar mast material to be used in a tripod I have for tuning and use a step ladder to reach the gamma match. Actually, my son climbs the ladder to do the tuning, I just read the analyzer and tell him which way to move the gamma tube. Also, I use a magic marker to put a line on the insulation of the inner element of the gamma match. Once you tune it close use it as your reference point. You can then slide the tube back and forth to check for any changes good or bad, but will have your point of reference to go back to. If you need to service the antenna for any reason, this also gives you a good start point to retune from.

AE7F
10-24-2011, 03:15 PM
You almost described to a T my situation. Mine is around 1.5 in the middle of the band. I can use a ladder to adjust raise/lower. Gamma match is as you described.

KE7IHG
10-25-2011, 02:50 AM
Your having fun on 10....I have a Cushcraft 10-4 which is a 4 element monoband that was a freebie. needed a little work but man o man am I having fun.
I don't have mine up very high maybe 22' but sure plays well to asia and the southwest:D

ad: elecraft