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[aprssig] APRS DFing SUCCESS with only an HT!

Dave Baxter dave at emv.co.uk
Fri Jul 27 08:00:38 UTC 2007


Nice one Bob...

I've used exactly the same technique to track down many sources of urban
QRM in the past, however it does get "interesting" when it's something
connected to overhead telco' or power wires, and they are radiating it
too.  The usual fix, is to get as close as reasonably possible with VHF,
then change to UHF for the final phase of the hunt.  (3rd harmonic)
Trouble with QRM, it's not always predictable of course, and it's not
unusual to find there is no 3rd "Harmonic", but there is another UHF
signal that is related to the VHF signal in some way.

I've also done the same with a portable broadcast MF radio on one
occasion.  The combination of the Ferrite rod's "dipole" response
pattern, and relative signal strength did the job.  That turned out to
be a next door neighbours portable TV, but only when it was in standby!

You do get some funny looks from Joe Public though...

In some parts of the UK, if you just turn up in a farmers yard, for
whatever reason, you will probably have some "interested and potentially
hungry" large 4 legged canine's coming for you, accompanied by a shout
of "Gedorf or moy land yer townie!"   (Get off my land you town person)
And if realy unlucky, two rounds of rocksalt coming at you too!...

As always, take care, and stay aware of your surroundings, and events
thereof!...

Now, if I could only get the HF QRO thermostat to identify its location
on APRS, a large area of North Bucks and South Northants in the UK would
have some happy HF operators in the winter.

I and others have failed for the last 10 years to find that particular
bar steward!...  It can be heard on 70cm's some miles away from where I
suspect it to be.  Close in (within a few miles) it's just too loud to
get any bearing on, even on 70cms, and it's signal strength varies with
each burst too, just to add insult.

I think I mentioned APRS, so very vaguely on the edge of the topic...
;-/

73.

Dave G0WBX.



> -----Original Message-----
> From: Robert Bruninga [mailto:bruninga at usna.edu] 
> Sent: Wednesday, July 25, 2007 8:57 PM
> To: 'TAPR APRS Mailing List'
> Subject: [aprssig] APRS DFing SUCCESS with only an HT!
> 
> To see a great view of DFing using only your mobile and an 
> HT, see the 5 map views of my track while recovering a tiny 
> balloon payload yesterday. (A key-chain 433 MHz oscillator 
> and tiny balloon (no APRS)).
> 
> These views are less than 100k images but very cleary show 
> how easy it is to find ANY RF source without any special DF 
> equipment, using only your mobile rig and HT with OMNI antennas.
> 
> 
> I have added this series of annotated map images and a 
> description to my usual APRS DF-ing web page:
> http://www.ew.usna.edu/~bruninga/dfing.html
> 
> Slide down about 70% down the page and look for HT-ONLY DF-ing:
> 
> Remember, on the east coast we don't get many balloon 
> launches because they all go out to sea.  So pardon my 
> excitement.  But this experience again proves, that we can DF 
> anything with just our own rigs if we just take the time.  I 
> have been preaching this for years, (usually from the APRS 
> perspective), but you simply don't need any technology.  Just 
> your ear and the ability to HEAR (and mentally visualize) 
> signal strength (quieting
> quality) and the patience to bracket the signal as you get closer.
> 
> Bob, WB4APR
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