Several days ago I had a telephone conversation with Scott,
W7SVJ, about putting a 2-meter AM repeater on the air in the
Phoenix area. Scott is actively pursuing this development
and we went over some of the system and operational
requirements and limitations that would be factors in
putting such a repeater on the air. Scott also suggested
that I write up a summary of our conversation and distribute
it to the local 2-meter AM community to stimulate discussion
either on the air or through the Arizona-AM Yahoo Group
(http://groups.yahoo.com/group/Arizona-AM/), e-mail or over
the air via the Tuesday evening 2M AM net. I am following
through on that with this note.

One only need look at the proliferation of FM repeaters to
see the benefits of such systems. Many, but not all, of
those benefits could also be realized with an AM repeater.
However, there are peculiarities with 2-meter AM operation
that must be taken into account to successfully utilize such
a system.

The most obvious benefit derived from a well-situated
repeater would be that we AM operators could hear each
other. The Phoenix Metro area is of such great extent that
simplex operation between even well-equipped stations on
opposite ends of the valley is often difficult if not
impossible. If the stations are less than ideal -- having
low antennas, low transmitter power, poor receiver
sensitivity or high external noise levels -- maintaining
contact becomes quite onerous. This is particularly true
for area-wide roundtables and nets where one often finds
oneself listening to nothing but noise for 5 to 10 minutes
at a time.

By having the assurance of hearing and being heard, another
benefit is realized -- increased participation. With a
repeater, it becomes fairly easy to add a minimal 2-meter AM
capability to most stations. A Gonset Communicator feeding
a groundplane antenna on the eaves of the house (or
apartment patio) becomes a communication tool rather than
being a curiosity with very limited range. Also, having a
strong signal from a repeater allows one to monitor the AM
frequency for random activity with the receiver squelch
closed. Such monitoring would expand the possibilities for
off-net QSO's and casual contacts and would fulfill the
promise of VHF-AM to be a reliable, round-the-clock,
short-range communications channel. These factors would
encourage more hams to give AM a try and to stick with it
once they are on the air.

Although not a priority for 2-meter AMer's, mobile and
portable operation becomes more probable with a repeater.
Think of the "Gooney Box" on a picnic table with a
coathanger wire stuck in the coax connector on top having
Valley-wide communication capability.

Given these benefits, how would such a repeater be
implemented? Here are the current parameters Scott is
working with:

1. Location: Backyard and tower for right now, perhaps an
elevated, remote location in the future.

2. Power output: 100 watts carrier with high-level
modulation.

3. Frequencies of operation: 144.45 MHz input, a
coordinated, standard 2-meter repeater downlink frequency
among the FM machines for output. In effect, the repeater
would be invisible for simplex operation on 144.45, but one
would only have to tune up-frequency a megahertz or so to
receive the repeater output.

4. Tone access: Not at this time. If problems are
encountered with intermod or FM/Packet interference, a
tone-burst on an audio frequency easily passed by AM
transmitters (eg: 1750 or 2250) could be used.

5. Repeater control: 440 MHz FM command receiver.

6. Antenna system: Single, medium-gain, omnidirectional
antenna for both TX and RX through a commercial-grade,
6-cavity duplexer.

7. Receiver: A commercial aircraft receiver with
state-of-the-art sensitivity and selectivity that is
designed to function in a dense RF environment.

8. Transmitter: Converted Motorola Motrac base station with
vacuum-tube final, plate modulated with a modified
Altec-Lansing PA amplifier running a pair of 811's.

9. Audio processing: minimal, with just enough audio peak
limiting to prevent overmodulation and low-pass filtering to
be compatible with repeater channel spacing.

As mentioned above, comments on and suggestions for this
proposed AM repeater system are welcome.

Jim, K7JEB
k7jeb@...