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10 element Cushcraft 2 meter yagi.

SMILEX2692002

Well-Known Member
Oct 26, 2011
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Just built a Cushcraft A148-10S 2 meter yagi beam. Hooked up 75ft of Lmr 400 to it and ran a test with my MFJ 259B. The antenna is only 5ft off the ground and is vertical. I also built the antenna to spec from the supplied instruction manual.

I found the SWR to be around 1.4 at 144, 1.6 at 145.00 MHZ, 1.4 at 147.00 MHZ, and 1.3 at 148.00
The antenna had a 1.1 SWR at 149 MHZ.

Now today it rained all day and the SWR was higher at all the above frequencies.

I did not use the supplied rubber cap that goes over the coaxial connector on the antenna due to my coax already having the PL-259 soldered on.

Now I understand the reading are not going to be accurate do to the antenna being so close to the ground at only 5ft. The instruction manual says for best results to have the antenna at least 10 feet off the ground.

Tomorrow I will have the antenna installed on top of my 40ft tower.
I'm hoping that the SWR of the antenna will come down when the antenna is installed on top of the tower.
The manual says in most cases the antenna does not need to be adjusted when built with the supplied measurements.

I will be using the antenna for FM simplex and repeater usage.
 

I usually just point them straight up for testing when they are down near the ground.

it should be fine once you get it up on the tower
 
The best place to 'tune' an antenna is where it will normally be mounted. That's also the hardest way I can think of. That setting the thing on it's hind end and pointing it toward the sky certainly will get things closer than if it was only 5 - 10 feet off the ground. Still won't be 'perfect' but that's also normal. People have been doing it that way for a very long time...
- 'Doc
 
Have it up on the tower at 45 ft.

The Swr is lowest at 144 Mhz (1.1 there)
At 148 Mhz the Swr is 2.0.
At 147 Mhz the Swr is 1.8, Its 1.9 at 147.200 Mhz.
At 146 Mhz the Swr is 1.5
At 145 Mhz the Swr is 1.3

No if was was interested in SSB the antenna would be perfect.
I'm using it for FM.

I find the Swr to be unsatisfactory with the factory settings. Although with 75 watts I was able to hit a repeater 105 miles to the NW away from me. The repeater is in the 147 Mhz portion where my antenna has the worst Swr.

I did not adjust the antenna before installing on the tower.
Looks like a trip up the tower to adjust the gama match is in my future.

Now the question is do I shorten the gamma match to lower the Swr ratio at the 147-148 Mhz range?

The factory setting was to raise the gamma rod 3/4 of a inch. If I'm correct then maybe shorting the gamma rod to 1/2 inch may get me closer to what I'm looking for.

My ideal situation would be to have the antenna have a lower Swr from 145-148 Mhz

Some were telling me to just buy a antenna tuner for 2 meters. I have always been one who believed correcting the mismatch at the antenna is the best way of fixing the problem.

Anyhow I now have 2 directional antennas on my tower. I removed a Imax 2000 that was mounted above my Sirio Sy27-3.
I mounted the Imax on a 5 ft pole I drove into the ground. I was able to tune the Imax 2000 for a near perfect match at 28.400 Mhz using my MfJ 259B.
 
Last edited:
...this sounds like a 2 man job anyway. One up adjusting the gamma match of the antenna and the other in the shack watching the MFJ 259B for better results.

... or you could take the 259 up the tower.

BTW: I never climb a tower unless there is at least one person on the ground watching me all the time,............. YMMV
 
If possible, I would agree about taking that analyzer up the tower with you, do any adjusting with it in hand. I think I would also make any adjustments in very small increments. It shouldn't take much to move your antenna's input impedance where you want it.
Good luck.
- 'Doc
 
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