[RFI] Portable DFing at HF

[Tom Thompson]

Kelly,

I can easily hear an S-7 noise on my 40m dipole at 700 feet with my AL 
loop.  With the larger CU loop I can hear even further or weaker RFI.

Tom   W0IVJ


On 8/12/2016 1:42 PM, Kelly Johnson wrote:
> I've located the source of HF interference in the past by getting a 
> beam heading with my 20m yagi, then walking that direction with an 
> FT-817 tuned to 50MHz.  For powerline noise, I then pull out a 
> portable (Arrow) 432MHz yagi to really pin it down to a pole.  The 
> last time I had a noise like the one that I'm hearing now was DF'd 
> with my 20m yagi and the FT-817 tuned to 50Mhz.  This time, the source 
> appears to be across a freeway in another neighborhood.  I was hoping 
> to reduce my neighborhood walk time by using a second directional 
> antenna to triangulate the source.  Unless the noise is extremely 
> loud, I wouldn't expect the loop to even hear it until I get close. 
> What I'd really like is a 20m yagi on a portable tower that I can 
> drive a block away and use to triangulate the source.  I think that 
> would work the best, but that's not a very practical option.
>
>
> On Fri, Aug 12, 2016 at 11:09 AM, Tom Thompson <w0ivj at tomthompson.com 
> <mailto:w0ivj at tomthompson.com>> wrote:
>
>     Kelly and all,
>
>     My experience has been that local HF RFI is almost always
>     vertically polarized unless you are very very close to it. This
>     means that the null is looking through the loop.
>
>     My last RFI hunt took lees than 15 minutes.  I took a reading and
>     determined the two directions the RFI could be coming from.  I
>     then walked about 100 feet perpendicular to the direction line and
>     resolved the direction ambiguity. Walking another few hundred feet
>     while twisting the loop for maximum signal located a Hobart Flex
>     180 battery operated welder in the garage of the house next door. 
>     By the way this was not my neighborhood.  The ham I was helping is
>     in the process of resolving the problem with his neighbor.
>
>     Tom   W0IVJ
>
>
>
>     On 8/12/2016 11:56 AM, Jim Brown wrote:
>
>         In off-list email, Kelly has said he thinks is noise is from a
>         grow operation, so I think he has to DF it on the HF band(s)
>         where he hears it. That means loop, so something like what
>         W0IVJ has posted is probably the way to go.
>
>         Another important suggestion -- a spectrum display is usually
>         the best way to nail down whether it's impulse noise or
>         electronic noise, but I don't think Kelly has one.
>
>         73, Jim
>
>         On Thu,8/11/2016 9:24 PM, KD7JYK DM09 wrote:
>
>             :I am trying to locate a new source of RFI in my
>             neighborhood.  I can get a
>             : decent direction in it from my yagi, but would like to
>             DF it from another
>             : direction to pinpoint the source.  I don't know if I can
>             DF it at VHF or
>             : UHF, but the noise is very clear on 20m.  Any ideas
>             about a good portable
>             : DF antenna for 20m?
>
>             I DF up to 950 MHz for two reasons.  One, small
>             directional antennas, two,
>             they usually aren't needed because as the frequency goes
>             up, the distance
>             goes down and you can usually narrow a source to a few
>             feet at that
>             point.  What kind of VHF and UHF equipment do you have
>             that can receive in
>             AM?
>
>             Kurt
>
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