Simplex repeater for PMR446 and CB-phones
How repeater works:
Repeater is used to increase signal range
re-transmit it by repeater.
Repeater is usually placed upper terrain or between these stations.
Example:
A-station cant get direct connection to the
B-station, because there could be too long distance or etc. hill between these
stations.
When using repeater, it is possible to get connection with transmitting turn by
turn.
Both stations must hear repeater and repeater must hear both stations.
A-station send and repeater receive.
A-station now ends transmitting and starts listening. Repeater sends A-station
message.
B-station hears now repeaters message.
B-station can now reply and repeater receives message..
B-station now ends transmitting and starts listening. Repeater sends B-station
message
B-station hears now repeaters message
and so on ...
Both stations heards own and opposite
stations, when repeater sends signal.
Traffic is simplex, other words alternately.
So this is often called "parrot-repeater".
Simplex repeater project:
At the one day i think this, when i was
using my PMRs, is it possible to build my own homemade simplex repeater.
After building my first prototype, i fitted it in the little aluminium enclosure.
And when i build and tested it, it came to look like this:
At front side there is power switch and 5mm dual led: green RX-led (receiving,
saving), red TX-led (transmit, replay).
On the left side there is DC-in connector. On the left backside there is transmit audio volume potentiometer and next from it there is D9 female connector.
With D9 connector, it is possible to reprogram PIC16F84A-microcontroller easily.
There goes RS-232 cable to the PC:s COM-port.
All electronics are fitted to aluminium enclosure, dimensions are: lenght 115 mm x
width 65 mm x height 30 mm.
At the inside picture there is
ISD2575 voice record/playback
chip and at right of it PIC16F84A microcontroller.
Recording time of
ISD2575 is 75 seconds.
ISD25XX chips are: 60 (8Khz),75 (6.4Khz),90 (5.3Khz) and 120 (4Khz) second
versions.
ISD2560 has best audio
playback quality.
Notice!: as this is old project (2005), today the ISD25** series sound chips have been discontinued by the manufacturer (Winbond).
Unfortunately, there is NO direct replacement for this part, and many suppliers
are already out of stock.
And there is now better replacement to PIC16F84A.
Repeater tested with Cobra MT-925 PRO, Cobra
MT-725,
Vertex Standard VX-146 and Ucom TwinTalker 4700 PMR446-phones.
© 1997 - 2010 Petri Tarkiainen