I agree with KQ2M that there probably is an intermittent someplace in
order for such a large change to occur, even though it's a given that
measurements at 5' aren't very predictive. Put the Beta match where the
manual says and track down what's really wrong.
Not to get you on a completely different path, but a very nice 4L OWA on
that 34' boom can be assembled without much effort. You throw away the
beta match and one element (well store the element for spare parts).
Adjust DE and D1 positions and lengths, and R & D2 lengths. You get
virtually flat 1:1 VSWR across the band with NO tuning required. Similar
gain as the 205CA. You give up some FB - it's around 17-18 DB across the
band. I've been testing one here for a while and love it.
GL, Steve K8LX
On 06/28/19 16:28 PM, Steve Walters K4IKM via TowerTalk wrote:
In the ARRL Antenna Book 21st and 22nd editions (and possibly other editions), there is a
section on optimized yagi designs for each band and at the end of that there is a section
titled “Modifying Monoband HyGain Yagis”. This discusses the strategy HyGain
took in their BA and CA designs, the CA being a better design, but goes on to give dimensions
that improve the F/R and SWR of the CA design.
I have built a 105CA and now a 205CA to these dimensions. the 10M design worked
out nicely however (so far) we have not been able to obtain a good match /
resonance / SWR with the 205CA optimized design dimensions.
My question is this: If you have actually BUILT this antenna did you adjust
anything other than the Beta Match (such at tip lengths)? If so, what distance
did you set your Beta match (and / or tips)?
So far, we’ve pulled this antenna up to about 45’ probably 20 times or more making gradual
adjustments to the Beta Match but we get a 5:1 SWR across the entire 20M band all the time. Tomorrow
I’ll get the analyzer to see if there is a resonance somewhere outside the band which will give me
more to go on. This was using the specified lengths / positions in the Optimized design. We’ve
checked and rechecked the dimensions and we are in very close agreement with the measurements.
We were able to get an excellent 1.03 SWR with the antenna 5’ off the ground by shortening the tips
by 4” on each side and adjusting the Beta Match. So maybe I don’t need a tower? Ha ha! Just
kidding, this is exactly what the antenna should be like at 5’ off the ground. The reason I mention
this is that the choke balun and feed line connections appear to be a-ok. We also tested the feed and choke
balun separately with open / short and 50 ohm loads. All looks good.
I’m hoping someone has BUILT this antenna and got it tuned. I guess I’ll get it
eventually but so far nada…..
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