Good question Paul. Remember the Mitrek RF decks are almost the same
used in the MSR2000 repeater, and with their tuned helical front end
make great receivers.
For the transmitter however, I would not run it on its own. Also
reducing the power output below 50-66% of rating might cause spurious
issues. The best is to get a manual and bypass the PA, running driver
power only. Then use an external amp to get your power up to where you
need it. This is how every Micor, MSR, MSF repeater is designed.
Motorola typically spec'd transmitters at 70.7% to get the best balance
from the parts, and typically used multiple stages to get there (i.e.
200mW-2W-15W-50W).
I recently picked up two 50W Mitrek Plus models that I will be using for
linking duty, and will be bypassing the PA on those as well. At only 10
miles driver power only should work, but I have yet to complete that phase.
Good luck on your project! You'll never know what duty cycle is needed
during an event, so better to overprepare than worry.
Tony
On 04/26/2010 01:47 AM, Paul Plack wrote:
After a few years on the sidelines, it looks as if I'm going to be
jumping back into repeater ownership. I have a few nice pieces left
from my last adventure, including a TX/RX duplexer and a loaded S-COM
7K, but I'm pondering choices in RF decks. This will be a local UHF
machine designated as an asset for a emergency net in a suburban area,
at a modest height, and the only RF device at its site.
I have two Mitrek 30w UHF mobile radios, and am aware of their
duty-cycle limitations, but would like to consider using them. They
have channel elements, and I'm not averse to spending the money to
have the elements redone properly. Looks like the pair will be 447.xx
transmit / 442.xx receive. I have a couple specific questions about
these radios...
(1) If Mitreks are converted for full duplex, how well do they work?
I'd like to have a complete, swappable RF setup, so trips to the site
are short, and repairs can be done on my bench at home. (As opposed to
requiring the two radios as separate receiver and transmitter.)
(2) Would it be a reasonable pursuit to adapt a larger heatsink, and
would that safely allow 100% duty cycle at 25-30 watts? (I'm
philosophically opposed to fans which introduce the opportunity for a
bearing to take the machine out of service.)
(3) Any comments on the front ends?
(4) I know these lack the sophistication of the Micor mobiles. Is the
lack of a circulator a big deal in this application, at an isolated
site with no other transmitters?
(5) Was Motorola's quality in the Mitrek era still good enough to
make a Mitrek preferred over, say, synthesized commercial transmitter
boards from lesser manufacturers, but of more current vintage?
All comments welcome.
73,
Paul, AE4KR
