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My new AO-40 2.4 GHz downlink isn't working

I turned it on this morning when AO-40 swung east over Central America (Az ~
170, El ~ 40; I am near San Francisco), and I couldn't hear any of the 6
listed beacon frequencies.  I followed the predicted track as AO-40 reversed
west and dropped below my western horizon several hours later.  But I DID
hear two data signals (2401.266 MHz and 2400.892 MHz) that seemed localized
on that Az-EL bearing (the signal dropped near zero when I moved 40 deg
off-direction). But I am disappointed not to hear any beacons at the listed
beacon frequencies.  Or any other SSB or CW signals in the down-link
passbands.  Perhaps someone can suggest a fix, or explain what is happening.

Here is my setup. I have a BBQ antenna modified for circular operation, as
follows. I covered the BBQ dish with aluminum screen and built a 5.25 turn
helical feed (CCW twist moving away from the observer).  I added the flat
shim-brass impedance transformer on the first 90 deg of helix, as people
describe.  I have a DEM LNA mounted directly behind the feed-helix' small
reflector plate, then 6 ft of good coax (TIMES LMR Ultraflex), and then the
DEM downconverter (to 144 MHz) is mounted about 2 ft behind the dish on a
counter-balance boom. I run 12 VDC on twisted pair to the RCA-type power
socket on the Downconverter, and I inject 12VDC into the 2.4 GHz coax just
above the downconverter using a DEM BT. To carry the IF I use 15 ft of
RG-58U to my receiver, an ICOM IC-706MkIIG.

A circular-converted BBQ ought to be about 21 dBi, so if the beacons were on
I should have heard them if I was pointed in the right direction at the
right time.  I searched around a bit, but still heard nothing.

Any suggestions would be welcome.

Eric, KN6KC

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