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Re: [linrad] re use of Motorola Micor's
The Motorola Micor was probably the finest crystal controlled two-way radio
ever built by Motorola. It was used by law enforcement and others in situations
that required performance when other services were operating nearby. The vintage
of this line of radios was in the 1970's (late 60's?). The mixer used in it is an ordinary
mosfet. A modern low cost DBM would probably do better. The key to its success was
its narrow band operation due to very high selectivity in the 5 pole helical filter in the
VHF version. Probably if close in frequency QRM is not too strong and even if strong QRM
a few MHZ or more away in frequency are present then the Motorola Micor could be seriously
considered as a converter for some implimentation of Linrad. It would be easy to use the
11.7 Mhz IF filters to provide a 15 Khz bandwidth. As Larry suggest, the Mixer is
sufficient in his location.
Modern Motorola radios and other brands use much smaller RF filters and the mixers
have a higher 3IP instead.
I use a UHF Motorola Micor mobil as a UHF repeater here in the shack. It plugs away for
years without maintainance. The channel elements are temperature compensated, so if
you are lucky enough to have the right frequency in one, the frequency drift will be very low.
I have just converted a Motorola Micor VHF exciter so it puts out the needed 116 Mhz
signal to mix with my 25 Mhz PLL. I changed a doubler to a tripler. The last doubler
is not needed and will probably be converted to a mixer to mix in the 25 Mhz.
If I break the emitter lead of the from ground and place a 2n3904 (I have a few thousand of
them) in series and drive the base with 25 Mhz, I should have a functional mixer.
The output filters will be re-tuned from 155 to 141.5 Mhz. This exciter produces 400 mw,
so I suspect I will have no trouble getting sufficient drive for a pair of TUF1h's.
I am in the process of re-crystalling the PLL CB so it outputs in the 25 Mhz range.
Since a 29.05 crystal is used in the PLL to put out 27 Mhz, a 27 Mhz CB crystal will put the
PLL into the needed 25 Mhz range.
73, Jim Shaffer, WB9UWA.
On 10 Jan 2003 at 9:26, Larry Kayser wrote:
> Jim and anyone else interested....
> >Since I like to rob Motorola Micors, I will also be using helical
> >from them to produce needed selectivity in the 144 Mhz RF path.
> Interesting, I have just become familiar with the Motorola Micor
> product Line. Here 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
> 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.