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[linrad] re use of Motorola Micor's
>Since I like to rob Motorola Micors, I will also be using helical filters
>from them to produce needed selectivity in the 144 Mhz RF path.
Interesting, I have just become familiar with the Motorola Micor product
I am using a 132-142 MHz version re-tuned to 144 Mhz with a Hi Side LO
injection. I find the
local oscillator string to be exceedingly clean and the Mixer is just
excellent. Since these
were intended for repeater service the receivers front end performance is
just excellent under
large signal conditons. I padded C118 to bring the L106 coil assembly down
to 5.3 MHz.
Specifically the Mixer Q101 is as good as any I have ever seen. I take the
output from C120 into a short coax
that feeds a crystal filter. The crystal filter is the 5.3 MHz IF filter
from a Low Band, Master Progress Line
Executive Series radio by GE. I mounted this filter in a small Pamona cast
metal box, paint removed, and the filter
output goes to a 2N5109 biased for 100Ma of current at 12V. A 2n5109 is a
somewhat tamed 2n3866 and is
extensively used in the CATV amplifier industry.
Even though I live in the sticks out here, I have very RF unfriendly Paging
transmitters both just above and just below
144-148 Mhz within 6 miles, line of sight. The previous RX's here, TR751,
ICOM 271, IC-706 have all had
strong reactions to these noisy paging transmitters, the Micor does not
show any indication of seeing them at all.
I feed this into a Time Machine demodulator and it works excellently. The
GE 5.3 MHz filter is somewhat unusual in that
it has minimal envelope delay distortion and gives me excellent performance.
Last but not least the LO multiplier chain in the Micor is also excellent
and very easy to drive with an external signal in
place of the usual channel unit.
The Micor is a really great basic RX, designed for excellent performance
under hostile conditions and for me it is
the best I have seen yet as a 144 MHz front end and converter.
Hope this is of interest to others.