[amsat-bb] Eggbeater Tuning

Dino Papas kl0s at cox.net
Tue Jul 29 22:14:30 UTC 2014

Rick - this may be totally unrelated but just in case…

I had a very similar problem with my Icom IC-910H and the M2 430 MHz double yagi I use here.  I found that the power output at several of the MHz increments between 430 and 440 MHz was down from the 75W it should have been, usually down to ~50W.  Straight into a dummy load I get full output regardless of the operating frequency.

At first I thought it must be the antenna, coax, cross polarization switch, preamp etc…never thought it was the rig…UNTIL I was talking to the Icom service guy who had just repaired the 432MHz driver on the rig.  I asked about the issue and he told me that the 910H on 432 was (1) particularly sensitive to SWR bumps and that (2) there wasn’t any way to fix it!  He actually didn’t like working on them (the 432 part) because even on the test bench any impedance bump along the way would in some cases cause the SWR power fold-back circuit to reduce the output.  He went so far as to say that he would only connect them directly to his service monitor without any other gear in the line like a Bird wattmeter so that he could work on them and not have that happen.

Again, don’t know if this applies, but now that you’ve mentioned it I’m going to have to hook up my recently acquired (and not tested except on the bench) FT-847 to see if I get similar results with my antenna system.

BTW, my M2 eggbeaters (both 2m and 432) both look absolutely flat  and we used it for our ARISS school contact as our backup antenna back in January.  If you’re using a M2 eggbeater check the SO-239 connection at the base; my original base actually had the coax center conductor break off internally after tightening the PL-259.  M2 sent me a new base although I was able to repair it myself just prior to our ARISS event and we actually ended up making the QSO on the eggbeater after problems with the primary setup.

Anyway, just a thought.

73 - Dino KL0S

On Jul292014, at 1754 PM, Richard Lawn <rjlawn at gmail.com> wrote:

> I was just attempting to work a station on AO-7 using my lake house setup -
> FT-847, eggbeaters, and Ubuntu with Wine running SatPC32, I noticed power
> was quite low on the 70cm output. I learned by tuning around the band and
> running output checks that apparently the rig doesn't like the SWR at
> around 432-433 mhz. I don't recall that there is any way to make tuning
> adjustments on the eggbeaters, but please tell me if I'm wrong.
> Rick

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