Hi Steve,
I have built 5 of these excellent antennas. There is nothing in the manual
that I have seen that tells you to alter the length of the Beta match from the
17” that is shown.
The only thing that you should be adjusting is the length of the element tips –
based on the freq. for which you want the lowest swr in your operating range.
I never got an accurate swr measurement except when I had the antenna mounted
on the tower, but I did get some useful relative minimum swr measurements with
my MFJ 269B with the antenna ~ 5’ off the ground.
Something apparently happened between 5’ and 45’ off the ground because the swr
changed from 1:1 to 5:1 with a flat curve. That is not normal.
A 5:1 SWR tells me that you may have a short somewhere in the feedline/balun,
or you may have put too much “gunk” in between the swaged element pieces and
therefore they are not making good physical/electrical contact – it is very
possible that something changed in the feedline/balun in those 40’ or something
changed in one of the elements.
I would suggest that you lower the antenna and set the beta match back to the
measurements shown in the manual, retighten everything and then take another
measurement at ~ 5’ with the antenna horizontal and see if you get a swr dip
somewhere in the band. If you are back to 1:1 at 5’, then see what happens as
you gradually raise the antenna. You certainly want to diagnose any possible
intermittents BEFORE you mount the antenna.
If you see a flat swr curve regardless of freq. at any height then you you
should recheck the feedline/balun – your problem is most likely there. If that
doesn’t resolve it, you should go through each swaged element piece and wipe
off excess “gunk” and then remeasure.
It may very well be something else, but this is where I would start.
GL!
73
Bob KQ2M
From: Steve Walters K4IKM via TowerTalk
Sent: Friday, June 28, 2019 4:28 PM
To: towertalk@contesting.com
Subject: [TowerTalk] HyGain 205CA OPTIMIZED
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…..
Tnx es 73!
Steve…. K3SW
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