Hi Yup, that covers it. It pretty well rules out (except at 3 MHz) other weird issues causing the problem.
Bob > On Apr 14, 2024, at 10:28 AM, Jordan Arndt <[email protected]> wrote: > > Hi Bob... > > Yes, I have an Ailtech 460 sig-gen, and yes, none of the bands are totally > dead. > > To check the sensitivity, I use the sig-gen at 50uV and again at 1uV, in AM > mode with 400hz modulated at 30%. I also use the Carrier Level meter and/or > the Line Level meter accordingly. > I also check to see if I can peak the internal tube noise by adjusting the > Ant Trim and checking for a peak in the noise as indicated on the Line Level > meter with the receiver input terminated in a 50 ohm load. > > Wth a 50uV input signal, the Carrier Meter shows a drop off below 8Mhz of ~ 4 > to 6dB per band, with the 3 Mhz band being the outlier showing a ~ 12dB drop > which I believe is due to a weak crystal which produces only 2.4Vdc at E-402. > The rest of the lower band crystals all meet the -4 to -11Vdc spec as > measured at E-402. > > Aside from a minor tracking problem in one of the 1st variable IF > transformers, the rest of the RF xfrmrs appear to be working normally and > track properly. I do note some scratching when the Ant Trim is rotated > quickly, but that only appears with no antenna connected. The Ant Trim peaks > normally on all bands. > > I hope this answers some of your questions... > > 73...Jordan VE6ZT > > ----- Original Message ----- From: "Bob Camp" <[email protected]> > To: "Jordan Arndt" <[email protected]> > Cc: "Collins R-390 HF Receiver List" <[email protected]> > Sent: Saturday, April 13, 2024 12:47 PM > Subject: Re: [R-390] Tracking down low sensitivity 0 to 8 mhz problem > > > > HI > > This seems to be running on for a while. > > Backing up a bit: > > How do you know the sensitivity is low at < 8 MHz? > > I’ve been assuming that you have a signal generator and have checked each of > the bands. I’ve also assumed we’re talking about “a bit deaf, but not dead”. > If any of that is not correct, then shame on me :). > > If this is the case, just how low are you seeing relative to (say) 9 MHz? > (are we chasing 6 db or 26 db?) > > Is it just as dead at (say) 600 KHz as at 1.5, 2.5 and 5 MHz? (is one of the > front end sections getting into the act as well?) > > The point being, some of us (ok, maybe just me ….:) ) may be making > assumptions that aren’t correct. If we are, our advice isn’t going to be > quite as helpful as it could be. > > Bob ______________________________________________________________ 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
