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

[K9MA]

I have noticed a similar phenomenon when testing transmitters using 
antennas, rather than attenuators. All kinds of garbage gets generated, 
apparently by every device in the vicinity capable of nonlinear conduction.

73,
Scott K9MA



On 1/22/2020 22:30, donovanf at starpower.net wrote:
> 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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-- 
Scott  K9MA

k9ma at sdellington.us