Two mornings in a row, different stations have QRM'd my QTH hundreds of miles away with readable CW at 60Hz across the entire 160m band. These were in pursuit of the Brunei DX-pedition running this week. Both stations have QRZ pages, only one, though with an email (which I contacted without reply). The other has no email link, but a photo of his 2.5kW dummy load. Both stations were S9-plus on two consecutive days when 160m was otherwise rather flat. So I'm asking, perhaps, an obvious question. Will this broad-spectrum 60Hz QRM for individual stations on a rare-DX freq be most likely do to something amiss with each station's power amp?
Were there any other stations with as strong signals as the "offending" stations on the air at the same time? What equipment are you using including antennas? Glen, K9STH
Did you have the noise blanker on? If so, was it on because of 'line noise'? A strong signal within the IF passband that the noise blanker sees will effectively 'turn off' the noise blanker. I hear this all the time on 80 M CW . I can hear W1AW for example pretty much across the bottom of the band simply because their strong signal messes with the noise blanker. Next time you hear the phenomena, turn the noise blanker off and see what happens.
A number of other stations likewise chasing the same DX, but yesterday and today, only one of those stations (a different each day, but the loudest among others) could be heard as 60Hz CW across the band. Rig is an Icom 745. Antenna is an end-fed random wire about 142m long: from 2m up to height of 12m, then horizontal by three equal spans of 44m to form a roughly equalateral triangle horizontal to ground at 12m. Have a dozen clamp-on ferrites at end of coax. There is an exterior MFJ autotuner so useless I never use it (due for removal). And about 10m of coax to an indoor tuner. Generally this setup does well on 160m, or I wouldn't be having that daily sked on 1812 at 6AM local.
8D: Are you using the pre-amplifier? If so, turn it off! The pre-amplifier can easily overload the receiver "front end" and all sorts of bad things can happen. Glen, K9STH
Suggestions for CW. Turn off noise blanker Turn off AGC Reduce RF gain to about 1/3 Increase AF gain to max Use the RF gain to control the audio volume.
I'd also suggest it's more likely that you have your noise blanker turned on. FWIW, when I ran mobile HF I often ran my noise blanker to deal with ignition noise. When I did it was common to hear strong CW stations up and down the band and they sounded like 60Hz keyed transmissions, IOW a buzzing CW signal that could be heard pretty much anywhere in the band. Remember, typical noise blankers place diode switches early in the receiver path before most of the rig's filtering. Those diodes create what amounts to wideband crystal detectors in the front end of the receiver and just like a crystal radio they'll detect strong carriers including keyed CW from strong stations. They can also lead to phantom SSB spurious products and lead hams to think someone is splattering all over them when it's just a noise blanker issue on the receiving end. Maybe you're not even turning your noise blanker on and what you're experiencing is different but it sure sounds like detection of strong keyed signals in your NB.
