A couple of numbers for posterity:
- Squelch opens at 0.2 μV.
- Full quieting is reached at 1.0 μV
- Modulation bandwidth is 9 kHz
- Deviation of repeated stations is 3.5-4 kHz
- Transmitter frequency error +30 Hz
- Power output is 20 W
- 70 dB reject on transmit.
KD5UGO provided several tons of test equipment and knowledge to operate it. We looked at the parameters quantified above.
We listened to the input frequency through the duplexers as well as straight from the antenna and we were looking at it on the spectrum analyzer at the same time; No unusual signals were heard or seen, only the signal of the HT (or the service monitor) we were using to key the repeater.
We "swept" the Bp (Tx) and Br (Rx) sides of the duplexer and found no anomalies. Yes, we wiggled wires and tapped on connectors while watching signals, none of which had any effect. We checked their tuning and were able to coerce another 2 dB of rejection from the receive side (I do not have the initial or resulting values, only the 2 dB difference). We saw no evidence that the transmitter on 147.06 was being heard by the receiver on 147.66 via the antenna system.
Bottom line: No Trouble Found.
Clearly, there is a signal from somewhere mixing with the signal being received from stations trying to use the repeater. None of the tests we did yesterday revealed the source of that signal. In fact, we saw no evidence of another signal. But it's there because we heard it on repeated stations within an hour of our visit. It's real, we just have yet to find it.