I think I may have found a problem. I have tried to run the STAGE GAIN procedures and, right away, the first test (connecting the signal generator to TP E206 and injecting a 4uv to 16uv signal) fails miserably to achieve -7v at the DIODE LOAD. It should produce that voltage with 4uv to 16uv input but it takes about 40uv to produce -7v. This is with the GAIN ADJ set to produce -7v with 150uv at J525. I'm thinking I have RF deck problems.
Thanks, Barry - N4BUQ On Mon, Oct 21, 2024 at 9:25 PM Barry Scott <[email protected]> wrote: > > For the past few months, I've been trying to determine why the noise > floor on the 0-1 MC band in my R390/URR is so high. If I tune to a > strong station, the noise disappears so, perhaps, "noise floor" might > be the wrong term for it but in places where there's little-to-no > signals, the noise is very noticeable and all but drowns out the weak > signals. > > If I switch from 0-1 MC to 1-2 MC (or virtually any other band), the > noise is reduced significantly. The difference can be on the order of > 15-20 dB on the carrier level meter. > > I presume this isn't normal but maybe it is. I think someone > mentioned that the noise on the bands under 8 MC are typically a bit > higher than the other bands but that doesn't seem to account for why > the lowest band is by far the worst of them all. > > There are only passives that change from 0-1 MC to the other lower > bands and I'm wondering if it's even possible for those to be the > problem but I don't know of anything else that could be causing it > either. > > I think someone suggested that the 1st crystal oscillator's output > might be low for that band but I seem to recall checking that on the > scope and output for the 1st and 2nd positions seems to be very close > to the same amplitude so I'm thinking that might not be the problem. > > Has anyone seen this and possibly have a cause for it? Like I said, I > presume this isn't normal but I don't know that for sure. > > Thanks, > Barry - N4BUQ ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
