Convert m120/gm300 from 12.5 to 25 khz spacing?

[erikj]

Through a miscommunication, I got two
12.5 khz spacing M120s when I thought I'd
get the 25 khz spacing. The price was good
enough where it would be worth some effort
to convert them if it isn't a huge pain.

These would be used for amateur radio stuffs,
not commerical.

I thought it might be a lost cause, but I saw
that some kits exist for some motorola radios
to go from 25 khz to 12.5 khz. I need the
other direction.

Does anybody have any ideas? Or should I
try to send them back if I can?

(These are model M44GMC00A3AA)

I have a friend with a service monitor who
may be able to assist me with the project.
Still, if it takes two weeks to do, perhaps
it isn't worth it to me

I know there are ways to crank the deviation
up, but I'm not sure what else would be
involved to make them "good" for transmit
and recieve.

I'd appreciate any suggestions. Thank you!

[eacradio]

erikj

I have used these units in a repeater before and the only thing I had to do was crank up the modulation. On the logic board just behind the main front conector are 3 blue pots. the back one will let you set the deviation up or at least they did on mine.
Danny

_________________
Keep on talking

<font size=-1>[ This Message was edited by: eacradio on 2001-11-21 08:23 ]</font>

[Monty]

Hi:

Hate to be the one to tell you, but
if you have the 12.5Kz version Boards,
you are kinda Stuck unless you desire to
replace alot of componets.

Most effect the Receiver, Audio and Dev Limits. Also just cranking the Dev Pots to Max, will do nothing more than cause distortion to be herd in the other radio.

About 3.2Khz is the max you can get out of
them, however, there are some resistors you
can change to compensate for that.

The receiver Filters in the 12.5Khz version is pretty
narrow.

I have the Parts list ( and its listed ) somewhere in the Batlabs Archives if you
are willing to hunt for it.

If I recall, the price on the conversion
parts is around 50.00, and takes about 1-2
hours of time depending on your skill level

Monty

[willbartlett]

Is't 3.2 k pretty close to what most unaligned ham radios run anyway? Most of the ones I've ever looked at are real close to 4K if they were over at all. This may also be a regional, speak-softly-but-drive-like-a-maniac, massachusetts thing :').

Will

<font size=-1>[ This Message was edited by: willbartlett on 2001-11-21 14:16 ]</font>

[Monty]

Hi:

Here is a repost of the original
message concerning GM300's with the
narrow vs wide boards.

Although I will take my hat off to anyone
who would make the necessary changes, rest
assured its not for the Atypical person.

Most of these componets are on the BOTTOM
side of the board, and requires removal of
the board and excellent soldering skills

Here is a Parts List of a typical 438-470
Mhz GM300 Board ( Wide vs Narrow )

C57 2113740B29 ( N ) 15pf
C57 2113740B31 ( W ) 18pf
C58 2113740B25 ( N ) 10pf
C58 2113740B27 ( W ) 12pf
C59 2113740B29 ( N ) 15pf
C59 2113740B31 ( W ) 18pf

THESE FILTERS ARE VERY IMPORTANT

FL51 9180097D04 ( N )455Khz 6F 3.94
FL51 9180097D06 ( W )455Khz 6D 4.00
FL52 9180098D04 ( N )455Khz 4F 2.40
FL52 9180098D06 ( W )455Khz 4D 2.65

R61 0611077B07 ( N ) 22K
R61 0611077B19 ( W ) 68K
R62 0611077A26 ( N ) 10
R62 0611077B09 ( W ) 27K

R163 0611077B23 ( N ) 100K
R163 0611077B17 ( W ) 56K
R165 0611077A98 ( N ) 10K
R165 0611077B03 ( W ) 15K

R301 0611077B03 ( N ) 15K
R301 0611077A82 ( W ) 2.2K

These Filters are Expensive, but have a
Impact on Receive Performance.

Y51 9180022M03 ( N ) Filter 45.1 Mhz 12.5Khz
( $53.00 User / Approx $40.00 Wholesale )
Y51 9180022M02 ( W ) Filter 45.1 Mhz 25Khz
( $26.00 User / Approx $20.00 Wholesale )

Anyhow, depending on how well you wish the
raido to work, you can either live with the
Receiver and crank the Dev to max, or you
can go the professional route.

Monty