30-03-2018, 05:22 PM
Well, I tried a few things while our midweek 160m net was on. First of all, the precise distance to the MW broadcast antenna is 2.9km. I had this very strong Broadcast QRM on the net frequency, and I could just make out the strongest station R-3. I had made up a series trap for 927kHz.
I had tried it on transmit previously, and it didn't affect the SWR. When I instered the trap, the strongest station went up to R5, but the QRM was still there. I tried the attenuator. This gave a marginal improvement.
So I then decided to try the 40m dipole. It's oriented with the end pointed at the Broadcast station, but way off resonance for top band.
It was a Eureka moment. The Broadcast QRM disappeared completely, and I was able to copy all stations on the net. All were complaining of QRN. I couldn't hear any QRN. One faint station joined the net, and the others were having problems copying him. I could read him R-5 even though he was further from me that the others.
In conclusion, I don't think we're dealing with a second harmonic, but just front end overload. I know that some 160m operators use a separate antenna for receive, but it hadn't occured to me to try the 40m dipole.
Ihave had a QSO with VK5ASF on 160m. He uses a highly sophisticated (and expensive) TMLA antenna, and from what I saw, it worked very well.
I may opt for a magnetic loop for receive only, which will probably cut down the cost by 90% compared to a transmit antenna, and use a relay to switch to my current 160m antenna on transmit.
I had tried it on transmit previously, and it didn't affect the SWR. When I instered the trap, the strongest station went up to R5, but the QRM was still there. I tried the attenuator. This gave a marginal improvement.
So I then decided to try the 40m dipole. It's oriented with the end pointed at the Broadcast station, but way off resonance for top band.
It was a Eureka moment. The Broadcast QRM disappeared completely, and I was able to copy all stations on the net. All were complaining of QRN. I couldn't hear any QRN. One faint station joined the net, and the others were having problems copying him. I could read him R-5 even though he was further from me that the others.
In conclusion, I don't think we're dealing with a second harmonic, but just front end overload. I know that some 160m operators use a separate antenna for receive, but it hadn't occured to me to try the 40m dipole.
Ihave had a QSO with VK5ASF on 160m. He uses a highly sophisticated (and expensive) TMLA antenna, and from what I saw, it worked very well.
I may opt for a magnetic loop for receive only, which will probably cut down the cost by 90% compared to a transmit antenna, and use a relay to switch to my current 160m antenna on transmit.