UHF Motorola Micor PA Filter/Circulator Question
rshprd
Looking for the procedure to tune the output network/circulator on a UHF
Micor TLE167xX assembly. This is the last stage before the RF power
amplifier and contains a circulator along with forward/reverse power sensing
circuits that feed the power control circuitry.
I am aware that the power control circuit can be bypassed. However, I would
still like to at least attempt to make the station function as designed. :-)
What little there is in the service manual really does not help, so any
information would be welcome.
Thanks,
R. Shepard
mailto:rsh...@home.com
WA8DBW
difficult at all. Depending on where the unit was tuned at the factory and
where you wish to put it, it may not require tuning. I place a Bird 43 watt
meter in series with the transmitter output and terminate the antenna port
in a good dummy load. If the reflected power is low enough - you are in
luck and have nothing to do. If it is high ( greater than 1.5 to 1 SWR)
then do the following:
Remove the cover an you will see six trimmer capacitors. There are two that
tune each of the three ports. Normally they will only require tuning if
there is a large excursion in frequency. I begin by tuning the two
transmitter port trimmers for maximum RF output and minimum reflected power.
Next tune the antenna port trimmers for max power out and minimum reflected
power.
Next disconnect the transmitter from the circulator and connect a dummy
load/watt meter in place of the transmitter. Connect a transmitted signal
on the desired frequency of any power level up to that of the repeater
transmitter in series with an SWR bridge or Bird watt meter to the antenna
port of the circulator. You should see no power indicated on dummy
load/watt meter on the transmitter port.
The Bird should indicate the transmitter power output and the reflected
power from the output port should be as low as possible and definitely under
1.5 to 1. If there is a need to adjust for a lower reflected power at the
desired frequency, adjust the two trimmer capacitors on the 3rd port that
feeds the 50 ohm resistor that is part of the circulator assembly for as
close to a 1 to 1 SWR as possible.
Go back to step one and if the SWR is still the same, all is well. Replace
the cover and recheck the SWR again. If there is a large change as I have
found in some units, then you will have to drill six holes in the cover
over each of the six trimmers so that you may adjust them with the cover in
place.
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*************************************
A quick and easier way to tune things is to use a transmitter other than the
repeater and feed the RF through a Bird inline watt meter to the Circulator
port 1 (J1011) with a dummy load/watt meter on port 2 (the antenna port) and
tune the four trimmers on port 1 and 2 for max forward power while
maintaining minimum reflected power. Next disconnect the dummy load from
the antenna port (port 2) and tune the two trimmers on port 3 ( the internal
50 ohm load resistor) for minimum reflected power and maximum forward power
at port 1.
That's it. Good luck and hope this is of some help. For a some what tong
in cheek but accurate explanation of how a circulator works, go to
http://www.wa8dbw.ifip.com/Circulator.html
By the way anyone have a MICOR UHF Tripler/low level amp assembly? I need
one!
--
Richard D. Reese WA8DBW
http://wa8dbw.ifip.com
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