Topband: Topband Digest, Vol 237, Issue 14

Jim Brown jim at audiosystemsgroup.com
Mon Oct 3 13:02:09 EDT 2022


On 10/3/2022 8:32 AM, Radio KH6O wrote:
> If a particular wide-band mode has caused the noise floor on 160 to
> rise 10-20 dB to the point where only QRO++ stations can be copied, I
> would say that this certainly is the proper venue for that discussion.

The cause of the enormous rise in the noise floor on ALL bands below 450 
MHz is the near universal use of Switch-Mode Power Supplies (SMPS) in 
anything that plugs into the wall, mandated by federal law 10-20 years 
ago, combined with gutting of the FCC that began 20-30 years before 
that. It has NOTHING to do with "wide-band" modes.

FWIW, the widest band mode in use on 160 is SSB, made worse by dirty 
rigs. Recent generations of Yaesu rigs have terrible splatter on SSB. 
There's a group of contesters in the Pacific Northwest that hangs out 
around 1844 kHz most nights. The waterfall in my P3/SVGA shows some 
signals whose traces are straight lines with about 2.5 kHz bandwidth, 
and there are others showing sidebands on voice peaks extending 2.5 kHz 
on both sides of the 2.5kHz transmitted audio, only 20 dB down from PEP, 
and the splatter QRMs frequency-adjacent stations. The same thing is 
clearly visible on any SSB allocations on higher bands. For the most 
part, it's not overdriven power amps, it's badly designed signal 
processing in the transmitters.

73, Jim K9YC




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