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Re: YABSQ (Yet Another Beginner's Stupid Question)



Unfortunately not supplying an answer, but I think you've hit the issue.
Quite an illustration of the principle we've all been talking about...it
doesn't matter how LOUD you hear it, it matters how much LoudER (than the
noise) you hear it.
I keep thinking I'm 1/2 deaf, since the MB only pushes my S-meter to S2,
but at 58,000km I get 100% good CRC on the MB (or at least I did last
Tuesday night, >100 frames worth).

One point to remember is the MB "should be" +10dB QSO, and with BPSK you
should be able to decode it very well down to about 7-8dB S/N (don't recall
offhand but I know it's < 10dB)...so you can do OK on the MB and yet be
-2dB QSO.

Which that much signal (+noise) power coming into your radio, I can't help
but wonder if it's intermodulating internally.  

And with that 13ULNA in front, your preamp should be just fine--like you
say, Gene's spreadsheet tells all and your "system", failing hardware
failure, is up to the task.

Downlink:
60cm solid dish w/ 2-1/4 turn helix feed allegedly 20.8dBic but I think
it's more like 17.5dBi-not-so-very-C
DEMI 2400-144RX d/c quoted <1.2dBNF 20dBG
120' Andrew FSJ4-50 1/2" superflex
Yaesu FT-726R

At 10:23 PM 8/16/01 -0500, Gerald Payton wrote:
>Hello All:
>
>Well, here is YABSQ (Yet Another Beginner's Stupid Question).
>
>First, let me describe my AO40 station:
>
>Andrew 26T-2400-1 Grid (BBQ) Dish Antenna:   24db GAIN
>DEM 13ULNA Preamp: 15db GAIN  .7 NF
>Millicom MC-251R (DRAKE TYPE) Downconverter: 27db. GAIN  3 NF
>Icom 820H Transceiver (assumed NF 13)
>(Distance to antennas is approx. 50 feet using LM400 coax.)
>
>Using the W3PM's AO40.XLS software and plugging in all these figures, it
>shows a relatively good receiving station
>
>In fact, I receive the Middle Beacon with a plus 20 to plus 30 signal level
>on the Icom meter.  Tonight it was varying and fading with a Squint Angle of
>about 34 and cloudy weather.  Using the AO40Rcv software, gives good and bad
>CRC's.
>
>I have been told that this is "about normal."  However, the other night was
>the first time that I was able to receive QSO's, other than just the beacon,
>and they were down in the noise without much audio.
>
>Question:   It seems to me to be a signal-to-noise problem.   If so, what is
>a remedy?  I have a preamp and reasonably good coax.  I realize that a
>better downconverter might help, but that's extra bucks.
>
>In addition, I find the beacon at differing "indicated" frequencies on my
>radio.  I am assuming that this is caused by drift from the downconverter.
>Excluding a dry ice application for stabilization, how may I stabilize the
>drift to be able to determine what the REAL frequency is while operating?  I
>can't  just say that "I think it's 145.xxx, or so!
>
>73,
>Jerry N5GPC
>
>
>----
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>
Scott Townley
nx7u@arrl.net
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