Hi Ted,
We should have been in touch sooner.
As you know, we eventually managed to reproduce the problem. The link responds to interference by dropping modulation mode as it should, but eventually sticks at 16QAM in the absence of interference. The problem is in the FEC decoder stage of the receiver. The link can be reset by re-establishing the link. We only seen the problem in your links that are exposed to high levels of interference from a radar station.
We provided some beta firmware that worked well in our lab testing and you kindly installed this in a standby link. From what we understand, this has improved the situation. However, the change is not 100% effective and we continue to work on this problem. We hoped to provide a fix in 650-01-44 but this fix missed the boat.
We'll be in touch with some more beta firmware as soon as we have a better solution. In the mean time, some more field diagnostics from links with the earlier beta firmware would be very useful.
Thanks, Mark