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Home Brew Remote Transmitter - Lightspeed - 28 January 2012
Sometimes it is desirable to set up a transmitter in a remote location a good distance away from your hide out.
Whenever we transmit a radio signal, that signal can be triangulated by Direction Finding stations. Remting the transmitter will lead any on trianglating your retransmitted signal to the Remote and not to your hide-out.
The attached diagram shows a way to "remote" transmissions from a PMR446 transmitter. [attachment=12] To work it is essential that the PMR transmitter has VOX circuitry which automatically transmits when sound is heard on the microphone input. It is essential to use high squelch levels or obsure CTSCC / DSC codes to reduce the risk of triggering of the "remote" radio by other stations. Obviously some form of solar charging would be desirable to keep the remote station on air 24/7.
Recent allowance of LPD (Low Power Device)frequencies to be used on license free PMR radios give the ability to use ultra low power to input to the remote a transmitter. Certain LPD frequencies are specified for licence free equipment at just 10mw and 100mw. Northern Raider's Intek 5050 (?) is ideal for this input. That low level power will ensure local transmission of signal so, will be less likely to be detctable over a wide area. I do not have anything that will transmit at this low power level, so am not entirely sure what range could be achieved with 10mw. Unobscured line of sight should give a range of 500meters or so. Really you want to be able to observe the location of your remoted transmitter in order to see if you are being DF hunted.
Alternate input solutions might be a hard wired intercom, provided you can run a cable to the remote. Or what about a wireless door bell?... some of these even have custom recordable messages, so you could rig a Channel 8 warning message of some kind. Channel 8PMR is a fairly widly used monitoring channel which I guess would be the primary open coms channel if that format were adopted as a universal comms tool after an event.
There are also devices called Repeaters and parrot repeaters that are available on e-bay for 50 to 60 quid that will do the same thing, in the case of the parrot repeater only a single ( preferably dual band) walkie talkie is required. An advantage of this type of equipment is that a properly equipped up-link / input transmitter is capable of signalling the device to turn it on and turn it off.
Have fun