> Bob, K8IA wrote:
>
> "...Until I recently erected a pair of K9AY loops, the noise was not even
> evident on my normal 160m antennas, a Inv V and an In L."
> ==========
> The noise from a well-filtered switching power supply is usually not
> noticed unless the antenna is close to the noise source, such as a random
> wire fed by an antenna tuner located in the ham shack or by signal pickup
> due to common mode coupling on coax feedlines.
>
> I know that the best way to cure a problem is to nip it in the bud at the
> source, however Bob's statement suggests that the switching power supply
> noise is being picked up by the coax feeding the K9AY loops. Try using a
> choke balun at the antenna end of the K9AY antenna feedline to see if
> this minimizes the noise to your satisfaction, Bob.
>
> 73, de Earl
---------------
While common-mode feedline pickup is a known culprit for this type of noise,
I'll put better odds on direct radiation. The quick test is whether the
noise changes as the pattern is switched. If it does, start fixing the
offending equipment; if the noise stays about the same, work on the feedline
issues, too. It's also possible that the noise is not radiated from a
single point -- switching power supplies with common-mode problems can use
your entire home's AC wiring as an antenna.
In my own installation, the loops are within 30 feet of the house and 40-50
feet from the nearest power pole, so I hear some noise. The noise drops
considerably when the loops are directed away from its source, so I know
it's radiated, not conducted.
73, Gary
K9AY
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