I recently built a portable 2m repeater that is about the size of a
bowling bag and weighs about the same. It is built into an SKB carrying
case that is rugged, dripproof, and good-looking. The secret of getting
a full-duplex radio and the duplexer into a box measuring about one
cubic foot in volume is choosing the right components and using a
widespread pair.
As a resident of Central California, my area is under the jurisdiction
of the Two-Meter Area Spectrum Management Association, otherwise known
as TASMA. This coordinating body wisely authorized a widespread
frequency pair, exclusively for portable repeater application, to be
used only for temporary and emergency situations. The frequencies are
147.585 MHz input and 144.930 MHz output. This is a split of 2.655 MHz,
which is just within the capability of a compact base station duplexer.
I chose an RFS/Celwave 5085-1 duplexer, which works perfectly in this
application. The 5085-1 duplexer is about 8.5 inches wide, 12 inches
long, and just under 2 inches thick- about 30% larger in all dimensions
than the common notch-type mobile duplexer. It comprises six helical
resonators in a notch-only configuration. Its insertion loss at RX is
1.1 dB, and at TX is 1.4 dB. The notch depth at RX is 92.5 dB and at TX
is 79.4 dB. These are very good numbers, better than what is needed for
zero desense in this application, and are roughly equivalent to four 8
inch standard cavities at a 600 kHz split.
The transceiver is a Motorola R1225, a programmable full-duplex radio
that includes both TPL and DPL capability, a built-in repeater
controller, polite Morse ID, courtesy beep, PA protection, etc. This
radio is what is inside a GR1225 repeater, and is available in either a
1-10 watt or a 25-50 watt model for VHF, and in 1-10 watt and 25-45 watt
versions for UHF. All versions will program into the Amateur bands
without modification. I am using the 10 watt model, since my ARES group
will use this repeater primarily for communication within a relatively
short radius. The model number is M03GRC90C2AA.
With a 5 MHz split at either VHF or UHF, a similar portable repeater
could probably use a common mobile duplexer.
73, Eric Lemmon WB6FLY
Dakota Summerhawk wrote:
Is the best way to have a mobile repeater up and running with two mobile
radios and a duplexer? Looking for a way to be able to run a couple of
repeaters, one VHF and one UHF, for a mobile communications van. Can
anyone recommend ways to cut down on weight and space?
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