[RFI] DFing an HF RFI source

Kelly Johnson n6kj.kelly at gmail.com
Mon Oct 2 21:26:59 EDT 2006

Thanks for the suggestion, but an electric fence would be highly
unlikely here in this suburban city of 30,000.  A more likely culprit
would be an electric blanket.  The noise I hear sounds VERY similar to
the recordings I've heard of electric blanket RFI.

On 10/2/06, Stu Benner <w3stu at myactv.net> wrote:
> Kelly,
> This is not a direct answer to your question but may lead you down a path to
> the source.
> My first guess at the source of this problem would be an electric fence,
> which would be an impulse (broadband) source. Day-to-day variations in
> amplitude are also consistent with an electric fence, the variations being
> caused by weather (moisture), vegetation, and other physical changes in the
> fence circuit. You may only be hearing it over a limited frequency range
> because the antenna (the fence) might be a more efficient radiator in your
> direction at some frequencies than at others. That effect could also combine
> with differences in your system (receiver plus antenna) sensitivity at
> various frequencies.
> A drive around your area while listening on the AM broadcast band may locate
> a candidate source. You could then backtrack from there to confirm that as
> the problem emitter. This is a slightly backward approach, but electric
> fences are usually easy to find.
> Regards,
> Stu Benner
> www.emcwizard.com
> -----Original Message-----
> From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
> Behalf Of Kelly Johnson
> Sent: Monday, October 02, 2006 7:57 PM
> To: rfi at contesting.com
> Subject: [RFI] DFing an HF RFI source
> I have an RFI source in my neighborhood that I'd like to track down, but
> could use some advice.
> The noise source sounds like a "click" or small burst of energy at
> approximately 1Hz.  In other words, I hear a burst of RFI a little faster
> than once per second.  It seems to be relatively narrow band. I don't hear
> it below 17 meters.  It is strongest on 17 meters, but I can sometimes hear
> it on 15 meters and maybe even 10.  I've never heard it above that.  I have
> DF'd the general direction using my tower mounted HF yagi and the RFI peaks
> at about S7 or S8 on 17 meters which is fairly strong, however I can't hear
> it when I walk the neighborhood in that direction with my FT-817 and a whip.
> I obviously can't carry a 17 meter yagi around the neighborhood.  What other
> decent antenna can I use to DF something doesn't appear to be broadband
> enough reach into the VHF region?
> FYI - The strength of this noise source varies from day-to-day and some days
> I don't hear it at all, but it's there most of the time.
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