Allen,
I'll echo the comments of those who've said 2m is not the best choice for a
portable repeater, due to the required close frequency spacing. A 440 MHz
repeater solves a number of problems regarding duplex operation.
I built a solar-powered repeater a few years ago, and had to operate it on a
very limited power budget. After looking at options, I used a Repco 2-watt UHF
transmitter sourced from an RFID application, and a companion receiver. The
transmitter drew only 650 mA at 1.8 watts output, and the receiver only another
22 mA in squelched standby. The controller was the most inefficient part of the
package, drawing 100 mA continuous. Still, I had four days' reserve battery
power even if the solar panel failed, assuming 100% duty cycle, using a
group-27-sized deep-cycle marine battery, which was rated at 105 amp hours.
If I had your needs, I'd do something similar, but using a much more
power-efficient controller. This would allow using a much smaller battery. SAR
outings often don't last more than a few days, so solar charging might not even
be necessary, especially if you could occasionally visit the repeater site with
a vehicle to recharge the battery. Also look into the options for small-scale
wind turbines. There are mast-mount generators available in the recreational
vehicle market that would easily hold up a small repeater in heavy use. They
look a little pricey, and not terribly durable, but for this application they'd
be great.
When looking for a transmitter, do your homework to find one which is efficient
at the power level you want. Most transmitters become very inefficient when run
below their rated max output. Choose one that's running full-bore at the power
level you need - it will use less current and dump less heat than a larger
transmitter dialed back. Some small crystal-controlled receivers have very low
current drain compared to their synthesized equivalents.
Regarding control, there may be locations at which CTCSS access will save more
battery current than the decoder draws. Especially if you're in the midst of a
bunch of public service agencies running enough power to overload your
receiver's front end, you're transmitter may stay up way more than it should.
If you really must use 2m, my first choice would be to modify a pair of
dual-band, full-duplex-capable handhelds to make a split-site repeater using a
UHF link frequency. The receive site wouldn't take much in the way of
mods...find a way to add a simple controller, and run low power with CTCSS or
DCS on the UHF transmit. The other end would need some sort of external
heatsink, and might need building a new enclosure for the radio, but you could
have 2-5 watts continuous if you needed it. Separate the sites by a half-mile
or more, and you're there.
But UHF would be much cleaner, and faster and easier to set up.
73,
Paul, AE4KR
----- Original Message -----
From: vhsproducts
To: Repeater-Builder@yahoogroups.com
Sent: Monday, August 03, 2009 11:09 PM
Subject: [Repeater-Builder] Portable repeater
I am in the design stages for a portable VHF (2 meter ham) repeater, and
thought I would solicit the views of the group for desired features. In broad
strokes, we plan on a computer programmable unit, capable of one or two field
selectable operation modes. CTCSS only, no COS or DTS. This is primarily to
support our SAR users (I manufacture the Micro-Trak line of APRS tracking
systems sold by Byonics-www.byonics.com) We will have DTMF remote control. The
goal is a bare-bones repeater, with no provision for a duplexer, so wide
channel separation and physically separate antennas will be a must. Battery
power will be the norm, and I am thinking of a system with no more than 8 Watts
output. What features are a "must-have" in this kind of a machine? What DTMF
remote functions do we need as a minimum, and are there any features that we
should have that other controllers don't offer? ( We will be writing our own
code for the controller, an Atmega microprocessor) Has anyone ever attempted a
servo controlled duplexer? Did it work?
73,
Allen
VHS
AF60F
