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Repeater Jammers How to catch them and deal with them Articles and reference material This page is presented to you by Kevin K. Custer  W3KKC Additions to it are welcome

There is no one solution to good DFing. A doppler DF unit is good for short or long duration transmissions, but not real sensitive (some better than others). A good yagi or quad beam mounted in the vehicle and hand rotated will work well on longer duration signals. An attenuator is needed with this setup, but a receiver modified with a variable RF gain control is better (why attenuate it just to re-amplify it?). problem is that any cable leakage between the attenuator and the receiver defeats the purpose of the attenuator.

FM receivers are not the worlds best units for DFing. They have a narrow dynamic range where an S-meter will work beciuse they have massive amounts of gain (a "limiter" stage is a nothing but a high gain amplifier stage). An AM receiver is much better for T-Hunting purposes but not many folks have all-mode receviers, and even fewer want to take them mobile.

One trick to get a lower signal level is to take advantage of the design of the transmitter you are chasing - they all "leak" a third harmonic slightly. Just program adjacent channels into your t-hunt receiver: one on the main channel, the other on the third harmonic. For example, let's say that you are hunting a jammer on the input of the 146.82 repeater - you would program 146.82 (to listen to the repeater output), 146.22 (the input), and 438.66 (the input's third harmonic) into three adjacent channels. When you get so close to the signal source that the 146.22 signal strength is overpowering then you switch to the 3rd harmonic 438mhz channel and continue there.

The best advice I can give you is to get some practice at an organized hidden transmitter hunt in your area, and see what they do and how they do it (the time to learn is not when the local system is being jammed). If there are no organized hunts, start one! Pick a simplex channel like 146.565 (a very popular foxhunting frequency), send a club member out to hide, and track him down on 565 and on 439.695Mhz. Scoring can be by least-time or by least-distance, or a weighted combination, and the winner hides next time.

Information on hidden transmitter hunting & equipment can be found at these sites:

Offsite link to the "Homing In" web page of Joe Moell KØOV       This web site started with Joe's column from 73 magazine.
While this web page is oriented to general transmitter hunting, much of the material is appropriate to repeater jammer hunting.

http://www.qsl.net/n6bg/thunt/

Articles about actually dealing with jammers:

Catching the Blue Knob PA. Repeater Jammer of 2004-2005   How Kevin and Scott caught the jammer of the Blue Knob 147.15 MHz machine.

Repeater Jammers  or, "God Luv Um", Nobody Else Does!       By Pete Policani  K7PP

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Note from Mike WA6ILQ:
Then again, occasionally t-hunting experience can be useful outside of established hunts... Years ago Ray Thill WA9EXP (SK) used to tell stories about t-hunting police cars in Chicago with bad or intermittent microphone cords... i.e. stuck PTT lines. He used to love to pull up behind a patrol car in his marked Chicago PD radio shop van and flip his wig-wag headlights on, then walk up to the officers and hand them a replacement palm microphone, and make some comments relevant to what the cops were saying... something like "I'm sure the captain appreciates the comments you were making about his ancestry".... they'd put his comment, their memory of what they were just saying, that and the new microphone they were holding together and get really concerned... then they'd let Ray swap the microphone and they'd go back on patrol... and wonder what was awaiting them in the ready room and the end of their watch....