Dan Zimmerman N3OX wrote:
> On Thu, Jan 8, 2009 at 10:02 PM, Ed Richardson <ed_richardson@shaw.ca>wrote:
>
>
>> Just wondering if anyone has experienced intermodulation caused by some
>> component in an antenna system? I am getting severe broadcast band
>> intermodulation across the 80m band and have ruled out the receiver.
>>
>>
>>
> Yes, I get very bad mixing of a local 1500AM station with CHU 3330 after
> dark; it shows up on 1830. At times before I added a BCB filter to my
> system, I could easily copy both stations simultaneously in AM mode to
> identify them. It didn't go away 100% but I knocked it down to a not very
> problematic level.
>
> However, last week I started getting BURSTS of IMD on the same frequency
> that appeared to be the same mixing product (though I couldn't really
> identify it). It was a windy night.
>
> I tracked the problem down to the (probably corroding) bearings in my very
> old Radio Shack junker rotator that I'm using to rotate the aluminum mast
> that supports my Moxon.
>
> I grounded around the rotator with some strap and that seems to have fixed
> the problem.
>
> This wasn't broadband noise from a charge/discharge across the junction or
> anything, this was bursts of noise in a small bandwidth around 1830.
>
> Look for dissimilar metal joints that might be a little corroded and bond
> the heck out of 'em ;-)
>
> Also check *actual diodes* in the system. K1TTT posted about subharmonic
> generation that he tracked down to some system component (the page doesn't
> seem to work in Firefox somehow)
>
No wonder. Look at the source. It's non standard, non compliant, mostly
java script using frames and probably written specifically for IE. My
system is not only not IE, but is set to not run java script and I'm
normally on LINUX.
73
Roger (K8RI)
> http://www.k1ttt.net/subharmonics/subharmonic_files/subharmonic_frames.htm
>
> 73
> Dan
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