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Author Topic: Long-Range direction finding  (Read 2512 times)

Offline jordan

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Long-Range direction finding
« on: September 12, 2014, 0224 UTC »
Here is a recent report of a couple of ham radio operators on the 40m band getting in trouble for not identifying on the air:

http://transition.fcc.gov/eb/AmateurActions/files/Kraje14_08_19_5521.html

But how do they pinpoint a location from so far away?  The letter mentions use of long-range direction finding techniques.  The FCC agent was in Maryland, and the two ham operators were in South Carolina and Delaware.

Offline BoomboxDX

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Re: Long-Range direction finding
« Reply #1 on: September 12, 2014, 0233 UTC »
I know the FCC has monitoring stations in various areas of the U.S. They probably have high gain directional antennas, and how closely they can pinpoint a transmission I really don't know.

But there aren't a huge number of hams in the U.S. Some neighborhoods may have one ham on the air, if that. My guess is that if they didn't use local trucks to pinpoint the offending hams, their antennas may be precise enough to pinpoint the neighborhoods in question, and then they just used satellite imagery to spot the house with the antenna -- probably cross referencing the FCC database.

But I'm just guessing here.
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Offline Rafman

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Re: Long-Range direction finding
« Reply #2 on: September 12, 2014, 0553 UTC »
The FCC has remotely controlled HFDF stations. They can dial up any HF signal on a frequency & using 3 stations, triangulate the "offender" with reasonable accuracy.

While the FCC does have "mobile units", they are used for more prioritized cases, like Public Service & governmental ones. I know of a ham who was visited by a mobile unit but it was not active case of jamming. These vehicles have fiberglass roof replacements, allowing multiple antennas to be mounted but concealed. Looking from the driver's seat, the antenna lines are run to various receivers on a control pod mounted on passenger side of the vehicle...

Hope this explains it but it is not that obscure to DF. The techniques were developed during WWII...

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Offline jordan

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Re: Long-Range direction finding
« Reply #3 on: September 12, 2014, 1125 UTC »
If this is the case, then how do all these SW pirates mentioned in the Logging board on this forum manage to not get caught by the FCC?

Offline John Poet

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Re: Long-Range direction finding
« Reply #4 on: September 13, 2014, 2044 UTC »
"On Tuesday, July 15^th and Wednesday, July 16^th, you were heard by a
   Commission employee operating your amateur radio station for 20 minutes
   without identifying in a timely manner.  The Commission employee used
   direction finding equipment and confirmed the transmissions were coming
   from your location.  The employee recorded the offending transmissions and
   provided undersigned counsel with recordings of the incident in question.
   Should you desire a copy of the recording, one will be made available to
   you.

  "This incident constitutes a failure to properly transmit your assigned
   call sign in violation of the Commission's rules. Your operation as
   described above is contrary to the basis and purpose of the amateur radio
   service as set out in Section 97.1 and is a violation of Section 97.119(a)
   of the Commission's rules.^ Section 97.119(a) states that "[e]ach amateur
   station . . . must transmit its assigned call sign on its transmitting
   channel at the end of each communication, and at least every 10 minutes
   during a communication . . ." Please be advised that the Commission
   expects you to abide by its rules."


The way this reads, the guy may have IDed at some point, but not the required amount of times... in which case the long-range DF would only have been used to confirm that the transmissions originated from the general known location of the licensee in question.

I don't believe the FCC would send a notice like this, based on a long-range DF only, without the operator having IDed at some point.  That seems more like a "guess".

"The Commission employee used direction finding equipment and confirmed the transmissions were coming from your location."

Ah-- so that does read as if they had an address from license records, and just used the DF to confirm that the signals originated from that general area.



« Last Edit: September 13, 2014, 2047 UTC by John Poet »

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Offline skeezix

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Re: Long-Range direction finding
« Reply #5 on: September 13, 2014, 2110 UTC »
Minneapolis, MN

Offline zackers

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Re: Long-Range direction finding
« Reply #6 on: September 16, 2014, 1541 UTC »
My Master's degree work was in using HFDF to locate transmitters using a single receiving site. By using the angle of arrival of signals from known transmitters with known exact locations, the unknown transmitter location could be determined within a few miles. That was in 1975. This is 2014. I have not followed up on technology advances in this area recently, but I imagine equipment has advanced considerably. Also, the FCC has multiple receiving sites, which would increase the accuracy. They would either have to guess the transmitting station's identity from their license records beyond that, or send a mobile unit to verify if they wanted to pursue the violation.

As was discussed in another thread here, the FCC doesn't seem to be too interested in going after SW pirates unless someone complains, and I am guessing that doesn't happen too often.
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