Topband: Wideband Noise on 160

[Tom Rauch]

Hi Ford,

> So what is it?  I placed my HP8553B spectrum analyser on the antenna. 
> Wow! The receiver is just picking up noise that really is at -70dbm (70
> microvolts into 50 ohms).  There is no "point" source.  It appears
> everywhere.  I've tried the MFJ version of the ANC4 noise canceller and
> was completely frustrated because that type of device will work great on
> single point noise sources.

Anything switching or arcing can cause a problem like that. Most 
likely it is something arcing, or switching very hard at a very low 
frequency (like a light dimmer, battery charger, or gas vapor lighting 
of some kind).

It is almost 100% certain not a BC station mixing problem. 
  
> significantly by 1750.  At 1830, the -70dbm is very real at the antenna. 
> I can hardly fault a receiver to being sensitive to signals!  The noise
> floor tapers off to an S3 level by the time you get to the bottom of 80
> meters.

What is the slope of sensitivity of the antenna you are using? 
Remember the antenna's sensitivity will change the noise level.
 
> I am struggling to interpret the information.  Are these stations spewing
> wideband garbage?  Looking at the second harmonic of the 60 over 9,
> 1600kHz AM station, the spur at 3200 is about 20 over 9!  That's ugly but
> hardly a reason for "wideband" noise.

It's really rare for a transmitter to make a noise like that at any 
distance.
 
> I speculate that the AM transmitters may be picking up noise fed back into
> their final tank circuits and "retransmitting" the noise back out.  Is
> this reasonable?

No.
 
> I also speculate that the nearby power lines can be absorbing wideband RF
> and re-radiating it to my antenna.  It is not insulator noise.  I am
> familiar with that type of noise and can locate a bad insulator (single
> point source) quickly.

I would look at the power lines, and what is connected to them. 
The amount of noise-generating junk today is unbelievable. I had an 
Igloo cooler that generated a noise like you describe in a switching 
12 volt supply. My Panasonic FAX machine is readable at 1000 
feet from my mobile!


73, Tom W8JI
w8ji@contesting.com


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