[CQ-Contest] [WARNING: A/V UNSCANNABLE]Re: Coax Stubs for SO2R

[RT Clay]

Yes, sometimes with interstation interference the problem is not coming from the feedline or antennas.

I ran into something like this at my station recently. One of my 20m yagis generated much worse interference on other bands compared to other antennas. The CW note on the interfering bands also had a rough "growly"  quality. At first I thought maybe there was a bad connection rectifying the signal. I checked the coax connectors and replaced the balun for that antenna. No change at all.
I finally figured out what was happening: the yagi in question is pointed (fixed) towards the house. When I turned the other 20m yagi on that tower towards the house I got a similar bad interstation interference. My shack is on the second floor. What was happening was that when the antenna was pointed at the house, the house wiring was picking up the signal and it was getting into my station from the AC line. Putting a large type-33 toroid on the AC feed reduced the interference quite a bit.

I still need to verify by running on battery power if there is some device plugged in somewhere in the house that is causing the problem, or if it was RF directly getting into the station power supply (Astron RS35) from the AC line. I also haven't compared a differential filter yet either. But a common-mode choke on the AC line did get rid of most of the problem.
TorN4OGW 


     On Thursday, September 10, 2015 5:14 AM, Jim Brown <k9yc at audiosystemsgroup.com> wrote:
   
 

 On Tue,9/8/2015 9:24 PM, donovanf at starpower.net wrote:
> That "growly" signals you're hearing are harmonics of your transmitted
> signal generated by unintentional radiators, especially switching power
> supplies. This type of RFI -- sometimes called "flooding" -- is caused
> by solid state devices flooded by intense RF fields (your transmitted signal)
> in which they were not intended to operate.

Great info! I've often heard this stuff, and wondered about the 
mechanism. It makes perfect sense. Thanks, Frank. Some questions.

1) Have you run into this with linear power supplies?

2) Do common mode chokes on wiring connected to these sources provide 
suppression? (In the case of rotator controllers, this would, of course, 
include the control cable to the rotator, and for all devices, the AC 
line cable).

3) Are conventional AC line filters effective for the power line 
component? What I'm really asking here is, "is the coupling to the noise 
source common mode or differential mode or both?"

73, Jim K9YC

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