Update:Thanks to Mark's very gracious help it appears clear that the anomaly is related to my radio and not my station set-up overall.
He had my radio in his shack (while I was operating his radio in my shack, having no issues at all with the noise floor) and observed the same exact problems with the noise floor. He also put the radio on the air for a serious work-out, doing rag-chews on AM.
Perhaps this is a "fluke," but Mark also experienced consistent drop-off of noise floor particularly after having been in transmit mode for an extended period, just like I did when the radio was in my shack. This, after the radio had been switched off for many hours, "cold starting" it the next day for instance. The noise floor sank dramatically only after a 1 minute or 2 of monitoring every morning and evening regardless of the temperature in my shack. Mark's shack temp is also much lower than mine (unless I switch the AC which I do when I get ready to get on the air). I had tried rolling back to P1 from P2 with no difference, seeing the same anomaly, regardless of shack temp too.
We also tried "cycling" through ANT1,2,3 (I am alluding to using antenna control on the form inserted below), hearing relays click and initially it seemed like this remedied the problem. This was done while my radio was in Mark's shack and I also tried it after I put the radio back in line in my shack. Perhaps doing cycling on the transmit side would help. I haven't tried it as of this morning.
- Ant Filter Tab.jpg (126.36 KiB) Viewed 1528 times
Last night, as I was getting ready for a sked on 20, I noticed that the noise floor went down again, tried "cycling," to no avail. I also went in transmit mode and noticed that the radio wasn't putting out any RF at all! The anomaly seems to be getting progressively worse as I had not seen this kind of behavior previously. Having trouble with PS not correcting well at times (I had observed this several times during the past few weeks) only to work very well after a few seconds may have been a harbinger of RF out issues.
We opined that the way the noise floor went and down as depicted in the waterfall wasn't necessarily consistent with a defective relay.
"The dip and rise in the noise floor isn't immediate, it takes place over about 1/4 second so there is a noticeable 'smear' in the waterfall, not a sudden 'on/off' sharp-edged delineation," as per Mark.As those who have been following this thread know, Doug, W5WC, has had my radio on the bench (twice already), but he couldn't reproduce the anomaly. He did not do a lot of transmitting though as I had reported seeing the anomaly while in receive mode, but somehow it would seem (I could be way off-base there) that extensive rag-chewing somehow "precipitates" the anomaly when in receive mode. He also swapped the PA/Filter board, and assuming that the antenna relays are on that board, it is very hard to imagine that the new board would have defective relays as well (again, assuming that we're dealing with a relay issue) that Scott also wrote several weeks ago.
Doug has agreed to dig into this more so I am shipping the radio on this same problem to him for a 3rd time!
73,
Juha
NI2M