from the page
http://www.repeater-builder.com/rbtip/sensitronRX.html

Modification of Micor "Sensitron" High-Band 150.8 - 162 mc. Receiver
RF & IF Board for use in 2 meter ham band.
by Kevin K. Custer W3KKC
Re-written August 19 2000, May 5 2002, and again on October 13 2002
because of coil availability.

Concept: To modify a TLD4073, TLD5273, TLD5773, or TLD8273 high-band
receiver for use in the 2 meter ham band. Please read through the
entire article before attempting the conversion. You may also be
interested in reading a Comprehensive Description of the Micor
Sensitron high-band receiver.

Background Theory: The Micor 150.8 to 162 MHz. high-band receiver is
the most common unit you will find in the used/surplus market. These
receivers were built in the day when most radio systems had only one
or two channels of operation. They were designed to be highly
selective from the standpoint of both the front-end and I-F stages,
and were made to operate on a narrow portion of the spectrum. Parts
for this type of equipment were specified to purposely limit the
tuning range. This allowed for more precise tuning and better
stability from both a mechanical and electrical view. Channels were
usually paired close together so the receiver would operate without
reduction in sensitivity as it was greatly reduced when trying to
receive more than a few hundred kilohertz from where the receiver was
tuned. Referring to the manual and parts list shows the intended
tuning ranges and the parts associated with them. The "Comprehensive
Description" link above provides more in-depth theory on how the
receiver operates, and its tuning ranges.

There are several different approaches of modifying the Micor
receivers named above for ham band use. One acceptable solution I
found is to change the 150.8 to 174 MHz. preselector coils to the ones
that are intended to tune the ham band. Placing longer or larger
tuning screws into the helical casting creates two problems. First,
the width of the bandpass is greater due to 'pulling' the high band
coil to resonance. Second, insertion loss is greater than if the
correct coils were placed in the casting. These two things are (in my
opinion) unacceptable in duplex repeater service, especially on two
meters. Research was done on pulling and other methods of making the
150.8 to 174 MHz casting tune the ham band. Go Here to view the
research.

Modification Description: You'll need to replace the old 150.8 - 174
mc. coils with ones that tune the 132 - 150.8 mc. range. These are
available from me, kust click on the helical resonator ordering
instructions link below. From the factory, all 5 coils are identical
except for the two end coils have wires soldered to them. Since you
are converting an existing casting, just salvage the wires from the
old end coils and solder them to the new ones at exactly the same
place from the grounded end. This ensures the correct impedance
point for the coils.

Helical Resonator Casting/Coil Ordering Instructions Click to
purchase new 132 - 150.8 mc. preselector coils or have the author
convert your casting to two meters. There are some options to choose
from.

The capacitors in the oscillator multiplier need changed to insure
these circuits properly tune the 2 meter ham band. Instructions are
given below for their replacement.

Modification of Helical Resonator Casting: Remove the "sensitron"
receiver "RF & IF" board, from the radio set. Remove the RF
preselector casting, by unplugging the small black wire on the output
end , and removing the 12 screws securing the casting to the circuit
board. Remove the 12 screws that hold the cover on the preselector.
Now remove the 5 helical coils by taking out the 2 screws holding each
resonator coil, and by unsoldering the input connection from the input
coil [leave the little wire connected to the input connector, just
unsolder it form the coil.] The use of a quality thin wall 7/32" nut
driver will make removal of the screws less difficult. Unsolder or
break the coil ground end connections with a pair of needle nose
pliers. The output coil has a small wire connected to it that passes
through a hole in the casting. This is the output connection of the
filter assembly that goes to the mixer. Simply unthread the wire out
of the casting then unsolder the wire from the coil and save it for
installation on one of the new coils.

Modification of RF - IF board: 150.8 - 162 model receivers will
require the changing of some capacitors in the oscillator/multiplier
section. Change C 108 to a 27 pf., C 109 to a 47 pf., C 110, to a 100
pf. (if already 100 pf and this stage still doesn't tune, make C 110
an 80 pf.), and C 113, and C 116 to 7.5 pF. It is helpful to do
these changes with the helical casting and all 5 aluminum coil shields
in the area removed to gain access to the capacitors. Refer to the
images below:

Go here for component and shield locations:
Coil Shields.
Component Locations.

Reassembly: Start the reassembly of the casting by installing the
salvaged wire from the old output coil by soldering it to one of the
new ones at exactly the same point from the grounded end with a
soldering gun or large enough pencil. This ensures the correct
impedance point for the coil. Install the new resonator coils by
inserting the two screws into the coil base and then carefully
dropping the coil, with screws down, into the casting. This makes it
easier to start the screws. Install the output coil first by
threading the wire back through the hole in the side of the casting
and securing the two hold down screws. Install the rest of the coils
by securing the screws first then make sure the coils are centered
inside each chamber and solder the grounded end of all of the coils to
the casting. A propane torch is handy when soldering the grounded
end of the resonators to the casting. I use a pencil torch as it
works well for this. Let the casting cool so you can handle it.
Next, solder the input wire to the input coil at exactly the same
point it was attached to the old coil, insuring that the little wire
doesn't short out against the casting. Finish by reinstalling the tin
cover and place the completed casting back onto the receiver printed
circuit board by securing all screws. Be careful not to over tighten
the casting screws as the printed circuit board is easily damaged.

Tune the receiver as per the Motorola manual. No other
modification's will be necessary for the above receivers to perform as
specified in the manual when tuned to the 2 meter ham band unless you
are using the optional AFC plug-in module. If using the AFC plug-in
module with the appropriate channel element, reverse the polarity of
diodes CR103, and CR104 in crystal discriminator portion of the
demodulator. These diodes are very fragile and it is difficult to
remove them without damaging them. Some people have had success in
simply cutting the diodes from the board, turning them and tack
soldering then back in place. If you are not using the AFC option
(most likely) there is no need to reverse the diodes as this would be
as useless as reversing the polarity of the speaker leads on a
monophonic radio.

Crystals, for the receive channel element (K1005), can be purchased
for the ham band from Jan Crystals at 1-800-JAN-XTAL
Complete channel elements on your frequency can be obtained from
International Crystal Mfg.


Copyright 1-30-1997 Kevin K. Custer W3KKC Any Comments? Send them
here e-mail Kevin

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In article ,
says...

from the page
http://www.repeater-builder.com/rbtip/sensitronRX.html

Modification of Micor "Sensitron" High-Band 150.8 - 162 mc. Receiver
RF & IF Board for use in 2 meter ham band.
by Kevin K. Custer W3KKC
Re-written August 19 2000, May 5 2002, and again on October 13 2002
because of coil availability.

snippety

Background Theory: The Micor 150.8 to 162 MHz. high-band receiver is
the most common unit you will find in the used/surplus market...

That's news to me. Last Micor of ANY kind I saw was back around
2000 at the Mike & Key ARC swap meet, and that was a UHF unit.

As for Micor parts: Good luck. Motorola stopped making them nearly
seven years ago. They're good radios, and the article is still relevant,
but it's a bit dated.


--
Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
kyrrin a/t bluefeathertech d-o=t c&o&m
Motorola Radio Programming & Service Available -
http://www.bluefeathertech.com/rf.html
"Quando Omni Flunkus Moritati" (Red Green)

john private smith wrote:

from the page
http://www.repeater-builder.com/rbtip/sensitronRX.html

Modification of Micor "Sensitron" High-Band 150.8 - 162 mc. Receiver
RF & IF Board for use in 2 meter ham band.
[...]

How do you modify Megacycles to Megahertz? Is it worth the trouble?

Dave
KZ1O


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Dave Bushong wrote in message et...

[...]

How do you modify Megacycles to Megahertz? Is it worth the trouble?

Dave
KZ1O

daves being funny........
"cycles" term for frequency back in the day.
"hertz" todays term for frequency
i think the switch happened back in the 50's or 60's but i bet dave knew that.