see http://www.amalgamate2000.com/sales/...x_repeater.htm
This unit is a small (83mm X50mmX25mm) , microprocessor controlled
simplex repeater and is designed to interface with any two way radio
with a speaker/mic audio accessory jack . The simplex repeater will
extend the range of any low power two way radio by being paired with
a radio on the same channel, as a intermediary placed at the highest
common point between the two radios on the same channel . The
simplex unit records the received the audio from the two way radio
and when finished receiving , enables the transceiver PTT and plays
back the recorded message into the mic socket of the transceiver, when
the replayed message has ended, it places a end of message "BEEP",
(this allows the listener to know the message was actually repeated)
then it allows the transceiver to return to receive mode for the next
recording . The unit is fully automatic runs on 4 AAA alkaline,
cells draws less than 40mA The unit will drop back into "sleep mode",
that extends it battery life and depending on its frequency of use,
will run for days/weeks. Plug adapter supplied is 2.5mm mic plug
(tip positive) and 3.5mm speaker plug, spaced at 10mm. NZ$100 plus
postage