[sci.electronics] DFing in the VHF World

jeff@virgil.UUCP (Jeff Koke) (03/23/89)

I'd like to know of any experiences (good and bad) regarding transmitter
hunting.  This past Sunday we had an impromptu hunt when an HT was
inadvertently keyed on the local wide-area repeater.  

It turns out that the HT was interfaced to a TNC and when power was turned
off to the computer, the TNC keyed the transmitter (which was on a power
supply).  The owner knew nothing of the problem and left his QTH to run (for
exercise).  The HT stayed on the air (keeping the repeater down) for ~2
hours.  This happened about noon.  

Once we got beam headings, three of us took off looking for it.  We
discovered the location in about 45 minutes, but had to wait for the guy to
show up.  It turns out that his VHF antenna was in the attic and that he
lived in an apartment complex.  Fortunately (for us) he had a 10 meter
dipole outside which helped in deciding what apartment door to knock on.
Upon his arrival he went upstairs and shut the thing down (finals were fried
by this time).  He also apologized profusely.  Anyway, it made for an
interesting afternoon.  We did all of our coordinating on 440 since the
three of us had dual band rigs in the cars.  

Suggestions are welcome.  I'll summarize all responses to the net.  

Tnx & 73,

Jeff

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-- 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Jeff Koke, KK4SN 	   |    Amateur Radio Emergency Services (ARES) EC  |
| EDO Corporation	   |    Amateur Radio, a National Resource !	    |
|		       ----+----					    |
| 814 Greenbrier Circle	   |  "And they said, Believe on the Lord Jesus     |
| Chesapeake VA 23320	   |   Christ, and thou shalt be saved, and thy	    |
| Horn: 804/424-1004	   |   house."       Acts 16:31 KJV	    	    |
| Domain: jeff@virgil.UUCP |						    |
| UUCP: xanth!virgil!jeff  |						    |
| Disclaimer: Verbiage written here is not associated with EDO Corporation  |
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keithm@wicat.UUCP (Keith McQueen) (03/28/89)

In article <1986@virgil.UUCP> jeff@virgil.UUCP (Jeff Koke) writes:
>
>I'd like to know of any experiences (good and bad) regarding transmitter
>hunting.  This past Sunday we had an impromptu hunt when an HT was
>inadvertently keyed on the local wide-area repeater.  
>
     [  stuff deleted for space...]
>Tnx & 73,
>
>Jeff
>

We had the same thing happen to us, (it was a misguided remote base...).
We found that a reasonable quick and dirty approach was an HT inside
the car with either the duck removed or a ??db attenuator inserted
could be used.  It seems that the signal could make it through the
wide front windshield much better than through any of the side windows.
So you turn the car in a circle until you get the strongest signal and
then drive in that direction.  The signal will suddenly drop as you
pass it (ie. as it becomes even with the side of the car.).  You then
take another reading and continue.  As you get close you may have to
remove the duck and maybe even shield the HT with your body to get
enough attenuation.

Have fun!

maa@nbires.nbi.com (Mark Armbrust) (03/29/89)

In article <391@wicat.UUCP> keithm@wicat.UUCP (Keith McQueen) writes:
>
>We found that a reasonable quick and dirty approach was an HT inside
>the car with either the duck removed or a ??db attenuator inserted
>could be used.  It seems that the signal could make it through the
>wide front windshield much better than through any of the side windows.

One day I turned on the cordless phone remote with the base unplugged and
heard another phone that was randomly going off-hook, with  short enough
pulses that it was sometimes dialing.  Usually got an intercept tone, but
sometimes got a very confused person on the other end.

I grabbed the handheld scanner and set off in search of the errant base.
The park across the street had one of the big metal trash dumpsters in it
so I walked around it with the scanner noting signal min/max to get a general
direction to set off in.  About a block away I could hear the signal with the
antenna off so I figured I must be close -- these are very low power xmitters
-- so I found a normal sized metal trash can and ran the scanner around the 
outside of it.  The opposite direction from the minimum signal pointed right
at someone's door, bingo!  (not really--I was off by one house, sigh :-( )

BTW, the guy who owned the phone had no idea that not only was it easy, but
it was legal to listen to cordless phones--lets hear it for modern technology)


--Mark