One thing to check is the DC feed, especially the ground return. I use a separate shielded cable, old RG-58 actually, and over the years I have had the DC ground open up, or become intermittent. Both times, it introduced significant RF noise. You can use the signal cable for the ground, but in my case that required a slight rearrangement of the DC grounds.
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Vince Fiscus, KB7ADL Sent: 21 January, 2010 10:28 To: [email protected] Subject: [amsat-bb] Landwehr 2m Pre-amp issue
I was suspecting my 2m Landwehr was having problems one day, don't know when it really started having problems, but last night I checked it out. Last night when I was listening to AO-7, when I turned the pre-amp on I got about S 7 of noise and the signals from the satellite were buried in the noise, and I couldn't tell that the signals were boosted much, but I could still hear them with difficulty through the noise. Turning the pre-amp off made hearing the signals easier, due to lack of noise. Obviously since I could still hear stations, RF is still going through the device. Checking it out on stronger fm signals, did seem to amplify them more, but I could tell there was still noise.
I don't know much about gaAsFet's but what I guess I'm asking, is when they Fail, could they fail in the noisy position, or when then they fail do they die with no amplification? I guess it could be possible some other component around the gaasfet failed making the device run wild. Maybe dirty relay contacts? The RF sensor still works still works fine.
I won't be able to get my hands on it for a while as there is too much snow on the roof yet, and I don't have weak signal noise generators to try to isolated the problems. Landwehr gives you a schematic but they didn't like to reveal too much. The pre-amp is about 16 years old. My 70cm Landwehr which is the same age and gets much more use is chugging away just fine. The 2m pre-amp is under an eggbeater. I don't need a 2m pre-amp on LEO's with the beam.
Give me some things to check, Thanks, 73 KB7ADL
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