Topband: 160 condx last night

[Herb Schoenbohm]

I had a similar experience here with trying to DF a 120 hz noise source 
on my TB Beverage antennas selector falsely believe the antennas would 
give some indications where the noise was in relation to the shack. The 
location was right at the Palomar Pre-amp which allows my Beverages to 
perform better on higher frequencies.  However it was not generated by 
the pre-amp at all but rather by a switching supply use to power it. (My 
other model of the same unit has it own internal DC supply and it was 
clean.)  By changing to a small linear DC supply solved the problem.  
Later by using a small hand help AM radio I was able to zero right down 
to the unit itself which was ironically clean except under load.

Some the tests we worry about about first on noise soures should be the 
ones we carry out first like powering the RX from a battery and pulling 
the power to *all* items internal in your house.  IMHO ersatz switching 
DC power supplies are probably the worst low frequency offenders and 
ironically the easiest to cure.  Yes I know....I used to carry a sledge 
hammer around in the trunk of the car while listening to 1690 AM until 
one day in the Minnesota winter night  a concerned neighbor called the 
police to report some "lunatic" was beating on power poles on his street.


73,


Herb Schoenbohm, KV4FZ







On 12/26/2013 1:22 PM, Jim Brown wrote:
> On 12/26/2013 6:22 AM, Shoppa, Tim wrote:
>> If anyone has any insight for how 120Hz impulse noise can just 
>> disappear below a certain frequency, that might help me find it.
>
> Several logical reasons that can happen.  1) The antenna radiating it 
> is more effective at higher frequencies. 2) The directivity of your RX 
> antennas with respect to the source is such that they reject the noise 
> on those lower bands. 3) It's not broadband, because it's 
> electronically generated. This is true of virtually all switching 
> power supplies, and many electronic sources. The noise from my SteppIR 
> controller and its switching PSU wipe out some bands and not others. 
> The PSU is worst on 12M, bad on the bands around it, but not so bad 
> lower in frequency.  Now that I've replaced it with a linear supply, I 
> hear the controller on the160M that's 25 ft away, so I have to turn it 
> off when I want to work 160M. 4) The source you're hearing on 40M 
> might not have been active when you were on 160 last night.
>
> 73, Jim K9YC
>
>
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