This is going to be hard to explain, but I'll give it a good try. On only one UHF frequency, and with only one operator, I am experiencing a momentary signal drop when he transmits. The signal is coming in strong and then his transmission drops suddenly and momentarily, not fades out, but drops completely for a couple of seconds and then returns just as strong as before. It lasts a few seconds and then the drop-off / return repeats. All other UHF/VHF signals come in fine and there is only an issue with this one frequency. Now for the technical facts. This is happening only on my mobile unit, which is an Anytone 578. As my antenna, I have a Diamond NR770HBNMO. I have tested this antenna on my antenna analyzer and it tests perfectly fine. This drop off issue does NOT happen on my HT, or my base unit for the same frequency and operator. I have compared the settings on all three devices for this frequency and all settings are identical. On my mobile, I have set my squelch to 1, but this doesn't resolve the issue. The operator, (on his base station) states that he can hear me very well and that my transmission to him is not breaking off or dropping out at all. Others also state that this particular operator's transmission is not dropping out on them either, and they can hear me just fine, as I too hear them without any issues. Now, this is a statewide UHF network, SARnet, where all 30+ SARnet repeaters are linked via microwave. I am about 25 miles from the nearest repeater, but again, this doesn't seem to be an issue as I can connect via my HT and base station. It does not seem to be a location issue as this drop-off can occur anywhere in my area and does not seem to be a localized issue, (not a 'dead-zone' issue.) The operator is transmitting from a county about 230 miles away off that local repeater, but as said, all SARnet repeaters are microwave linked, so this isn't an issue either. Since all comms are set identical for this frequency, I am starting to wonder if it is an issue with the radio but have no real way of checking. Other local operators cannot seem to find the source of the problem as well. Does anyone have any suggestion(s) as to what I might check that I may have overlooked?