(4 November 2013, 16:25)CharlesHarris Wrote: I was merely pointing out that no rf communication available to civilians these days can be considered "secure." As for DFing unlicensed users, at least in the US, law enforcement asks us to assist only when the unlicensed users are causing interference with a licensed service. In the Washington, DC area there was a group of fellows using CB radios transmitting on the 10m amateur band, dispatching a pirate taxicab outfit which were putting out spurs getting into some fire department radios, so our volunteer group was asked to locate them. We rolled up their whole operation in a few days, police and FCC raided the taxicab office, confiscated 16 taxicabs and radios, and deported a bunch of illegals without "green cards."
Much more fun than chasing and recovering nweather balloons, which we also do regularly for the National Weather Service.
If you want to be discreet and low profile you shouldn't say anything over the radio you would not want to read on the front page of The Times. That's all.
As for "countermeasures" when we practice the "fox hunt" the fellow hiding with the transmitter uses a narrow beam directional with good side rejection and the highest possible front to back ratio. He also uses the lowest transmit power in the narrowest bandwidth, taking advantage of terrain shadow and reflection. Microwave burst transmissions with narrow focussed directional wave guide are state of the art. Keep transmissions short. Use frequency hopping. The cadets at VA Tech are experimenting with laser burst transmissions to send data over line of sight paths. All is good fun for geeks.
Thanks Charles,
Agreed that using equipment available and affordable to us normal folk, that every radio transmission should be considered a public broadcast, and that we must exercise caution with what we say on air.
Direction finding a taxicab firm and weather balloon is not complicated at all, as neither employ any form of Opsec operating protocol. Taxi firms make almost continuous high power transmission on a very predictable frequency. Weather balloons have fixed frequency and fixed timing of transmissions albeit at lower power. Both of these make for easy triangulation.
The guys in UK who succeed when playing cat and mouse with direction finders have developed a self-preservation operating methodology that is very similar to military radio operating protocol:
- Keep transmissions very short, use code words and pulses of dead keying.
- Change transmission locations often
- Transmit and receive on different frequencies
- Keep power used to a minimum
- Change transmit and receive frequencies very frequently (frequency hopping).
- Use of narrow bandwidth (Select the narrow mode on the radio’s programming)
Pulse coded laser beam transmission has already been discussed in the coms section of this forum. Technology is available off the shelf that allows voice modulation over laser. We are currently experimenting with laser coms and the biggest issue faced is reliable alignment of between field portable transmitters and receivers as the beam-width is so narrow.
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