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  #21 (permalink)  
Old 05-23-2017, 11:06 AM
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Originally Posted by KK4JUG View Post
Several years ago, we were looking for an aircraft beacon. We quickly determined that it was coming from a predominately residential area and there certainly were no downed planes there. Since there was no downed plane, the resources committed to the event were limited: one CAP captain, one EMA officer and myself.

Ultimately, we used an Icom (I think) portable. We removed the antenna and inserted a small plastic and wire plastic bag tie. Then, holding the radio very close, I turned very slowly waiting for the signal to come and go. It was finally pinned down at a local high school. It turns out someone had donated an old air frame for the school to do with it as they wished. However, they failed to remove the beacon and when the would-be mechanics started playing with their new aeronautical toy, they set off the beacon.

A very crude direction finder but it worked great.
That's how the majority of the CAP ELT responses go these days still, some malfunction or another, heh. And believe it or not we still train to body-block with a handheld or a paperclip in the DF unit as a quick workaround.
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Old 05-24-2017, 5:14 PM
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Originally Posted by jonwienke View Post
GLOBAL TSCM GROUP, INC. - Radio DF DDF2020T

Can calculate a bearing to a transmitter in less than a second.
I don't mean to get off topic here, but isn't this similar to the LOJACK system?
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  #23 (permalink)  
Old 05-24-2017, 5:23 PM
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Same principle exactly.
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Old 05-24-2017, 5:44 PM
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With Lojack, the presumption is that the local PD will have at least two cars equipped with LoJack's Doppler RDF equipment. You'll see four whip antennas mounted as corners of a square, on the roof or trunk. Each car gets an "instant" bearing to the transmitter and if the two cars have good separation (which means they both must be out on patrol, preferably several miles apart) then you take the two bearings and look at the place where they cross.

But if you are one ham, with one RDF unit that you have paid out for (several hundred bucks overall) then you need to take the bearing, plot it on a map, move to another location, take another bearing (assuming the jammer is still active), plot a cross...and that's more time, energy, and money than most hams or clubs can manage to raise.

Also, if you are in a big city, the steel and masonry canyons create a lot of multipath, and simply getting a true bearing that isn't just misleading echoes, is not assured.

Best done in teams of two (one to drive, one to operate the gear) at the same time, so now you need four people, two cars, two RDF set-ups. Or, you need to keep going out night after night and trying to pin the jammer down. Again, more than most clubs or repeater operators can commit to.
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Old 05-25-2017, 8:58 AM
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If you are going to rally some hams to go searching for this guy. Maybe don't discuss it on the radio. If he knows you are looking for him. He may go quiet until the heat dies down, and then start up again.

Go to a local club meeting, and talk to them in person and come up with a plan.

I dont recall seeing if you mention where about you are from. Maybe some one from here would like to help.
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Old 05-25-2017, 8:50 PM
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A doppler unit on a car or house then sending that info via a phone, one person can track down an offending signal. A doppler allows you to df on the move. Just follow the lights and you can drive up to the door, or with an attenuator, up to the person in a crowd, A doppler is the really easiest way to track a signal. Some units, are in kit form, about $150 dollars. Then attach to a radio, scanner , or some receiver. I use an old AOR 8000 radio, which allows me to hunt hf signals up to uhf signals. My unit gives bearing to the station as you move around.
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Old 05-26-2017, 12:02 AM
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The DDF2020T goes a bit further when attached to a computer with GPS running Google Earth. When the offending signal is on the air not only do you have a bunch of LEDs around a compass dial, you press the space bar on the computer and it will draw a line from you to the offending transmitter on a Google Earth map. Do this from several locations and just drive to where the lines intersect on the map.
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Originally Posted by teufler View Post
A doppler unit on a car or house then sending that info via a phone, one person can track down an offending signal. A doppler allows you to df on the move. Just follow the lights and you can drive up to the door, or with an attenuator, up to the person in a crowd, A doppler is the really easiest way to track a signal. Some units, are in kit form, about $150 dollars. Then attach to a radio, scanner , or some receiver. I use an old AOR 8000 radio, which allows me to hunt hf signals up to uhf signals. My unit gives bearing to the station as you move around.
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Old 05-26-2017, 1:50 AM
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Originally Posted by Rred View Post
ROFLMAO.
You're absolutely right. All you need, is to have the entire NYPD pissed off at you, big time, and a state senator motivating the FCC. Without that?
There was a particularly troublesome jammer in California who was recently stopped, essentially through the efforts of one man with a doppler DF unit.

The FCC expects hams to be self policing as much as possible, hence the appearance of a "hands off" attitude. They will actually step in and help, but they expect the hams to have done their homework first.

In the several cases I have participated in, the source was tracked and identified, and the details, including the methodologies of tracking, were documented and provided to the FCC. They did the knocking on the doors.

In the recent case I mentioned above, the FCC wasn't involved at all. My point to all this is, your results will vary, depending on the effort you put into it. But a $400 doppler unit and some time can be a very effective deterrent.
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Old 06-01-2017, 2:14 PM
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Originally Posted by rfradioconsult View Post
When living in the Dallas area we held monthly foxhunts, some guys used beams and others (myself included) used Doppler's. With a Doppler you just drove and observed your direction indicator, no need to stop and take beam headings. The Doppler guys almost always found the fox first.
Funny you mention this. When I was young, I was involved in the Plano radio club and would occasionally hitch a ride for their foxhunts (rabbit hunts they called them). There was a group of guys that also came out with a Doppler set up in their pickup truck and would likewise beat everyone to it. Some people got a bit annoyed with them, but I always thought it was a cool set up they had.

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Old 06-01-2017, 2:46 PM
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The advantage of doppler DF is that the faster you're moving, the better it works. No stopping to take a reading.
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Old 06-01-2017, 3:16 PM
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It's almost all obsolete now. If you PO the FCC enough, they just call their military buddies and have any illegal transmission plotted and pinpointed in seconds via satellite!!
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Old 06-06-2017, 7:10 AM
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Had a guy years ago causing issues. He bounced between three repeaters causing issues. One day I got fed up with him and called a couple of other hams and we started talking on one of the repeaters while he was messing around on one of the other two and we had a pretty good idea he was listening. So for about a hour or so we would call out random headings and say the direction that one of us were going and we would track it down and notify the FCC. As soon as he got quiet one of the guys said that the interference stopped we all acted like we would be stationary until it started again.About an hour later he started back up. One of the guys said he had to be within a block of where the transmissions were coming from and the transmissions stopped. Did not have an issue after that.
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