Topband: Spurs

Dan Zimmerman N3OX n3ox at
Thu Apr 21 06:59:19 PDT 2011

>  It would appear that a strong sig on 25m
> and another on 31m could produce this effect. My  8 circle receiving
> array elements are 23.5 ft long and are resonant somewhere around
> 10 mHz so would deliver strong signals from both bands. The spur
> seems to be caused by overloading in the rx preamps as it was not
> on the tx vertical.
> has anyone else noticed this?

Sort of.  I have one like that 1830  that's strong local AM BCB on 1500
mixing with CHU on 3330.

It's usually not very strong and I didn't identify it until it got really
bad and I heard the distinctive "pings" of CHU and then found the AM station
on another radio.  It would come and go for a while, and I think may
have often been there as a weak signal because of slight preamp

But one night it got really strong and started bursting in and out.  That's
when I discovered that the strong, troublesome mix was happening in the
bearings on a cheap rotator I was using under the mast holding my 20m Moxon
rectangle.  I fixed it by putting a ground strap across the rotator.


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