[Collins] Reluctant filter switch on 51J-4 - Solutions?

[Glen Zook]

I don't know what frequency meter cost over $50,000
back in the 1970 to 1980 time frame, but it certainly
wasn't anything that was sold by Motorola, General
Electric, RCA, or any of the other two-way radio
manufacturers that I know of.

That was the time frame that I owned the Motorola
reconditioned equipment center for the south central
United States and I bought 5 service monitors (which
were the latest and greatest thing that were available
for two-way service) over a year's time.  They covered
100 KHz to 999.9999 MHz in 100 Hz steps that were
controlled by lever switches (the service monitors
were made by Sytron Donner).  There was a calibrated
analog meter that showed the transmitter's frequency
to less than 100 Hz.  With a deviation meter,
deviation oscilloscope, and broadband mixer they were
$3,995 each in 1970.  Of course they also had a signal
generator that was controlled by the same frequency
switches as the frequency monitor, as well as
transmitting frequency standard and deviation monitor.

Cushman came out with the CE-3 during that same time
frame which was a little bit cheaper than the Motorola
but did not cover anything except the two-way radio
bands up to 470 MHz and later 512 MHz.

Those service monitors are still legal to use today.

The 51J series does NOT meet FCC accuracy and
stability requirements for two-way radio and has not
since about 1952 when commercial FM went to +/- 15 KHz
deviation (from basically unlimited deviation - but
generally in the +/- 25 KHz range) and 0.005%
stability.  In 1957 the standards changed to +/- 5 KHz
deviation on lowband and highband with 0.002%
stability on lowband and 0.0005% stability on
highband.  In 1965 standards for the 450 MHz band went
to +/- 5 KHz deviation and 0.0005% stability on the
mobiles and 0.00025% on base stations and control
stations.

The 51J series is an excellent general coverage
receiver.  In fact I have a 51J2.  However, the
factory specifications in terms of both frequency
accuracy and stability definitely did NOT meet the FCC
two-way radio requirements even in the 1950s, let
alone the 1970s.  Besides, just to read deviation (FM
modulation) on a 51J4 you would need to modify it with
a Foster-Sealey discriminator and associated circuitry
on the output of the discriminator.

I know that no Motorola owned Service Station would
ever use something like a 51J4 as a frequency
standard.  As for independently owned MSS (Motorola
Service Station) using a 51J4 as a frequency standard
would not be approved by any Motorola Service
Representative (these were employees of Motorola that
made regular inspections of the Service Stations to
insure that everything meet Motorola specifications). 
Now an independent two-way radio repair shop (not
affiliated with any of the major two-way
manufacturers) might try to "get away" with using
something like a 51J4.  However, since in those days
the FCC had monitoring stations all over the country
and they definitely were monitoring the two-way radio
bands, I certainly wouldn't want to have such a repair
facility work on any equipment that I owned.

I worked for the MSS in Atlanta, Georgia, my junior
year at Georgia Tech (1965 - 1966) and the test
equipment that we had was MUCH better than a 51J4.  My
senior year I went to work directly for Motorola and
established the very first Motorola owned portable and
pager repair facility located anywhere outside of the
Schamburg, Illinois, plant (this was before the
Florida operations, Texas, Israel, etc.).  In this
facility I definitely had the best test equipment
available and none of it cost more than $2,000 per
unit.  I believe that my total test equipment value
was less than $7,500 and this included special "jigs"
and adapters for the portable and paging equipment as
well as for the "normal" mobile equipment which I had
to be able to service if a Factory Technical
Representative or Field Service Representative brought
in that the local MSS was having problems.  This was 4
years before the service monitors became available
(they became available in 1970).

The first service monitor that I got when I owned the
reconditioned equipment center was serial number 117. 
It turned out that this one was the 7th one that
Motorola shipped anywhere in the world.  In fact, it
was "hand built" by Systron Donner which I found out
when I wanted to use a specific "plug in".  I had to
make a minor modification in the interface to allow
the "normal" plug in units to be used.  The other 4
service monitors that I bought had all of the
"updates", etc.

Glen, K9STH


--- Wn4i <wn4i at arrl.net> wrote:

Never in my life ......I remember working for Motorola
using a 51J4 back in the 1970-1980 every days as a
frequency meter (recalibrated on  every bands )  with
no Problems whatsoever ...in order to recalibrate  two
way Radios for polices , fires , ambulances and taxi
driver ....At the time a frequency meter was over $
50.000







Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco


	
		
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