So I put up my system last week, and it did a beautiful job. The coax loop antenna at the time was mounted low, between buildings, using non-shielded CAT6 cable. After playing around with enclosures, I put it together (with the coax shields grounded to the amp board), and everything went to the dogs:
1) One loop has gone deaf. Probably a short between the shield and the center conductor, but could be a break in the conductor somewhere, I've used the continuity detector, and haven't found it. yet. Thinking I might have blown an amp, I cross-connected the inputs and both responded identically, and both responded properly to gain changes, so it's not the amp board.
2) The loop which works now has a big 45 KHz signal on it. It can pick up lightning amongst the noise, but it's always there. And it's got intermod with some AM band stations (at least is sounds like it when I listen to the signal on the buzzer). I get a clean signal on my radio (FTdx3000), unmodulated S7 carrier (on an antenna tuned to the ham bands, so it's pretty strong). You can see it here:
http://frankfortweather.us/BoStaSig/orem1155/index.html , green signal.
So I have two questions, should anyone know the answer:
1) Have I missed some way a receiver can go deaf? I'm getting tired of confirming things work...I need to find the thing that doesn't.
2) What transmissions are at 45 KHz? I can find nothing in my Klingenfuss or online. Perhaps it's something more local/short-range. I can null it out on a NE-SW direction in Utah (on a line pointing toward Australia on one side, New York and Europe on the other).
EDIT: There is a third question: what is causing the intermod? There are no mixers in the amp, so it must be coming from the first adjustable-gain amp. That amp has the full-bandwidth signal, so it must be intermod between two strong signals present in the antenna. A 50 KHz difference could be caused by two local AM station, but not 45 KHz. I need to recheck the frequency in the system. I can hear a 45 KHz signal using my ham receiver, but maybe what's getting into the system is different. Ill check that, and do a quick survey of local AM stations, see if there is a 50 KHz difference somewhere.
EDIT: two stations, 1400 KHz and 1450 KHz are each +40 dB on my ham antenna.
MORE EDITS: okay, it's intermod in the first gain stage. I can turn the gain of stage 1 down to 1 and increase the gain of the last variable amp, and the intermod goes away. So it's manual settings for me for a while, or the servers can be programmed to recognize modulated sine waves in the signal and move to a preference of low gain in stage 1.
So now I'm left only with the question of why the red channel is deaf. I'll keep working on it. It must be mechanical. I apologize if this sounds like a dubug log, but that's what it's become.
LAST EDIT: All fixed. I don't know what I did to wake up the red channel , but in taking it apart, testing for continuity, and reassembling, it worked.