HFU HF Underground
Technical Topics => Equipment => Topic started by: Teotwaki on June 03, 2019, 1343 UTC
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This topic is related to the loggings of fishing Drift Net Beacons being monitored in these threads:
https://www.hfunderground.com/board/index.php/board,40.0.html
https://www.hfunderground.com/board/index.php/topic,54162.0.html
I ran across this web page about the Japanese RDF set TAIYO TD-L1706
https://www.cryptomuseum.com/df/taiyo/tdl1706/index.htm
The TD-L1706 is a mobile radio direction finder (RDF), developed in the late-1980s by Taiyo Musen in Japan. The TAIYO TD-L1706 was developed primarily for use aboard ships, for finding the direction to a beacon and for locating fish. It was soon discovered however, that the device was also suitable for locating (clandestine) transmitters on land, not least because of its very compact antenna.
In the Netherlands, the Radio Monitoring Service — then known as RCD — first started using the TD-L1706 in the late 1980s, in combination with their custom-built PAN-1000 intercept receivers.
Block diagram from the very nice web site Crypto Museum
(https://www.cryptomuseum.com/df/taiyo/tdl1706/img/tdl1706_setup.png)
Display unit pix from the very nice web site Crypto Museum
(https://www.cryptomuseum.com/df/taiyo/tdl1706/img/302893/001/small.jpg)
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Those things are neat! A bit out of my price range however.
Today we have tdoa to play with as long as we have innernet service and those willing to let us use their sdrs, but it'd sure be nice to have one of the stand alone df units.
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Those things are neat! A bit out of my price range however.
Today we have tdoa to play with as long as we have innernet service and those willing to let us use their sdrs, but it'd sure be nice to have one of the stand alone df units.
How big is a TDOA unit at Driftnet Beacon Frequencies? ;D
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I expect tdoa to get progressively more accurate as development continues, but who knows.
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I expect tdoa to get progressively more accurate as development continues, but who knows.
accuracy is a whole 'nother matter so let me rephrase the question
Size is determined by the frequency you want to operate at.
Typical ham radio 2 meter (146 MHz) handheld TDOA has elements that are not too big .... about 38" for each end, about a half wavelength of 1 Meter
(https://www.byonics.com/images/tdoa6.200.jpg)
The questions restated are: How big will TDOA antenna elements be for a 2MHz driftnet frequency? About 75 Meters.
Since we can't have a practically sized handheld approach maybe some sort of SDR based approach might work where antenna size might not be so critical?
https://www.rtl-sdr.com/localizing-transmitters-to-within-a-few-meters-with-tdoa-and-rtl-sdr-dongles/
http://www.panoradio-sdr.de/tdoa-transmitter-localization-with-rtl-sdrs/
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Please don't mix up TDOA and goniometers...
Well, modern goniometers are some sort of time difference based, but with receiving antennas located within a half wavelength space, so there is no doubt that the antennas receive the same period of the wave. With such a short time difference, the hyperbola arm is practically a straight line, thus giving a bearing. A goniometer can give the direction of an unmodulated wave.
On the other way, real TDOA systems are based on receivers located many wavelengths away from each other. Even if they know perfectly their locations on earth, they cannot locate a pure carrier, because periods are not numbered. They need to detect the phase of some modulation with frequencies low enough to allow some time difference to be measured with some confidence.
Then there is a much more tricky problem when the waves are not received along the earth surface, but reflected by the ionosphere : the heigth of the reflecting point is not the same for each receiver in the system. Maybe in the middle of the day or in the middle of the night, with at least 3 receivers perfectly spaced around the unknown transmitter the system begins to give something next to perfect location.
I would like any further discussion to distinguish between those 3 cases defined above. Thanks.
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hi,
I have 2 TD-L1706 DF units, i also having RS232 interface on them.
I use mine in a fixed DF network i have.
Im using on one site, one TD-L1706 with the flat antenna, one 3g/4g modem, one ICOM PCR1000 that is modified with 10,7 MHz output.
Two IP/RS232 converters, and a switch.
I remote the PCR1000 and get the bearing from both sites.
I made my own map software and radio control, so i only key in frequency and mode one time and software send it to both sites.
The TD-L1706 works really nice.
The system works very well. I get two red lines on the map, and the crossing shows the transmitter location.
Im working on to get sound also, and i think im going to use a small little software called IP sound.
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hi,
I have 2 TD-L1706 DF units, i also having RS232 interface on them.
I use mine in a fixed DF network i have.
Im using on one site, one TD-L1706 with the flat antenna, one 3g/4g modem, one ICOM PCR1000 that is modified with 10,7 MHz output.
Two IP/RS232 converters, and a switch.
I remote the PCR1000 and get the bearing from both sites.
I made my own map software and radio control, so i only key in frequency and mode one time and software send it to both sites.
The TD-L1706 works really nice.
The system works very well. I get two red lines on the map, and the crossing shows the transmitter location.
Im working on to get sound also, and i think im going to use a small little software called IP sound.
Very cool!