[RFI] [CQ-Contest] 40m to 20m interference

[donovanf at starpower.net]

Hi Bill, 


You're experience is fairly common. When a transmitter operates in 
proximity to electronic devices, the strong RF field often causes those 
devices to behave in a non-linear fashion to: 
- generate harmonics of the strong RF signal entering the device, and 
- modulating signals normally present within the device onto the 
harmonics. Signals mixed onto the harmonics can be AC power or 
digital signals. 


No amount of filtering of your transmitter or receiver will resolve these 
problems. Its highly likely that some electronic devices in your own 
home are the culprits, but if you live in a suburban neighborhood your 
neighbors' electronic devices are likely to cause problems too. 


The first step -- as with any RFI investigation -- is to turn off the AC 
power (and battery power) to 100% of all the electronic devices in 
your home. All UPSs in your home must also be turned off. If the 
RFI goes away or is reduced, its time to isolate the devices. Use the 
individual circuit breakers on your home to help you do this. C ommon 
culprits are wall wart power supplies -- especially switching power 
supplies -- and rotator controllers. 


Isolating RFI sources in neighboring homes requires similar techniques 
and unusually cooperative neighbors... 


Good luck with your hunt! 


73 
Frank 
W3LPL 

----- Original Message -----

From: "William Hendrick" <whhendrick at yahoo.com> 
To: donovanf at starpower.net 
Sent: Thursday, January 23, 2020 12:34:06 AM 
Subject: Re: [CQ-Contest] 40m to 20m interference 




Yes, covers most of the band and of course the closer you get to the harmonic the worse it gets. For example if TX1 is on 7030 and TX2 is listening on 14030 only the strongest signals can be copied. Buzz could be a good description. In my original post I still wonder if I'm asking too much for the filtering to handle. 


Bill, N0AC 




On Wednesday, January 22, 2020, 06:06:10 PM CST, <donovanf at starpower.net> wrote: 







Hi Bill, 


Please describe the interference you're experiencing, you described 
it only as "a lot of interference" 


Is the interference only directly on the second harmonic of the 40 meter 
transmitter or does it have buzz sidebands that cover much of the 20 meter 
band? 


73 
Frank 
W3LPL 







From: "William Hendrick via CQ-Contest" <cq-contest at contesting.com> 
To: cq-contest at contesting.com 
Sent: Wednesday, January 22, 2020 11:00:29 PM 
Subject: [CQ-Contest] 40m to 20m interference 

I have a lot of interference on 20m when TXing on 40m even with BPF on each K3 running 100w. A 23' shorted stub at the 40m rig doesn't seem to help. Both antennas are Butternut verticals about 150' apart. Am I asking too much for the filters with the same antenna polarization and spacing? 
Bill, N0AC 
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