Re: K3: 160m SWR issue

Posted by Julius Fazekas n2wn on Nov 04, 2009; 7:15pm
URL: http://elecraft.85.s1.nabble.com/K3-160m-SWR-issue-tp3940644p3947473.html

Hi Brian,

The TopBand query that you reference had a situation that may or may not apply to your setup. He only had 15' of feedline between the Tx and the antenna. Weird things can happen.

Phil's situation was somewhat remedied by adding a longer run of coax.

I've had my share of issues on 160 as well, even without running an amp, because the base of my antenna is VERY close to the transmitter (>30').

Several things cleared up my issues including better matching at the antenna, and isolation style 1:1 current choke and partially buried feedline.

You can't count on the K3 (or K2) SWR reading 1:1 or some other low value. You really need to see what the impedance of the antenna is in real and imaginary terms. Several antenna measuring devices and the LP-100 will tell you this and you can better match the antenna. You're not lost if you don't have access to such tools, often a good choke balun will moderate some of the problem, if not eliminate it altogether. See Jim, K9YC, RFI and choke tutorials.

160 presents some interesting technical challenges, but they aren't are draconian as some would like you to believe.

Hope this helps.

73,
Julius

Brian Machesney wrote

I'm feeding a "double L" antenna on 160m (visualize a vertical dipole with
the top and bottom legs bent to form something like a capital "C" and fed in
the middle of the vertical leg). The SWR bridge on the K3 shows 1:1 SWR, but
when I fire up my Alpha 91B, I see significant reflected power.

I recently saw a post on the topband reflector from another K3 owner whose
160m output power is being reduced from 100W to 50W by the K3 even though
the SWR reads 1:1 on the K3's internal SWR bridge.

Has anyone else seen this or have an explanation for it?

--
73 -- Brian -- K1LI
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