Motorola recieve crystal 44.645 in mobiles

[Satelite]

Hello:
Several of the Motorola mobiles use a 44.645 crystal for the receive oscillator .
for examples GM300 and Maxtracs.
My question is on flea bay I have been seeing an auction that has for sale a 44.685 crystal they claim is the Motorola rx crystal.
Ive only seen the 44.645 crystal in the Motorola mobiles I been repairing over the years.
My question is did Motorola actualy use a 44.685 rx crystal in there mobiles and if so what radio and band was it used in ?
Thank you
Satelite

[jackhackett]

Do you have a link to the auction? I couldn't find anything except ones for 44.645.

I don't know of any radio that used that freq, the other common 2nd oscillator freq is 44.395.

[Satelite]

Hello jackhackett:
Yes hes ebay seller electronicsweet2012
His auction title is:
Radio Accessories 16 Channel Machine Receiving Crystal For Motorola GM300 44.845
Ebay auction number 112156078837
If you look at picture of the crystal it does indeed say 44.845 not 44.645.
Wonder how far off the difference would push the rx ocsilator ???
Or what advantage one could get by using a 44.685 rx oscillator crystal.
Reason I'm asking qestions is I have run into newer ford pickup trucks and newer john deere combines that with Motorola vhf mobiles at certain freqs get a constant birdy on receive .
I think I might be able to possibly swap out a 44.645 to a 44.845 and try to calibrate back on freq and see if just by some chance of luck I can solve the rx issue.
I do know the old Johnson ppl 6050 crystal vhf mobiles used an if 10.7 crystal and when this happened the Johnson shop changed the 10.7 if to something else and then rx worked from what the shop techs say anyway.
Ive never done or even tried but wondering now.
Satelite

[jackhackett]

Okay, you keep calling it "44.685" instead of "44.845" so that is a bit confusing.

Yes, some radius radios had a 44.845 2nd oscillator, which would put the first IF at 45.3 MHz instead of 45.1 MHz (add .455 to the 2nd oscillator to get the IF). You can see on the Batlabs GM300 page that the letter after "GM" in the model number determines which IF is used, C for 45.1, R for 45.3.

http://batlabs.com/gm300.html

To use those crystals you'd have to have the matching 45.3 MHz crystal IF filters and some other components might have to be changed as well.

[Satelite]

Hello jackhackett
Dang it yes my ooops.
I thought I had corrected all the wrong crystal freqs.
But your correct I'm really meaning to say 44.645 versus 44.845 not 44.685.
Wish I could blame it on too much bud light but I'm not much of drinker so must be old age
And I thank you for the link ill go read that now.
Thank you
Satelite

[Satelite]

Hello;
I do see a 45.3 listed for the gm300 model number .
For example M44GMR29C3A was one I came up with from the graph which I googled with no results so tried m34 and m43 and m33 as well with no hits from google.
I also dug out my gm300 repair manual and looked at every rf bd schematics and found only the 44.645 crystal in y52 location and no mention of a 44.845.
Every gm300 I ever saw sold or repaired her was a gmc not a gmr .
but it is indeed listed on batlabs graph as also a 45.3 along with the normal 45.1 I normaly see used.
Has anyone else ever actualy seen the 44.845 crystal in a gm300 ?
If so what was the model number and or band and power output ?
I even went so far as to look it up in my M120 repair manual and it uses a 44.645 crystal as well rather than a 44.845
Oh well curousity killed the cat they say and I don't have a radio here with one in it for repair so no big deal just wondering about it.
Thank you
Satelite

[jackhackett]

I'm guessing this was an option for customers that had problems with an image signal or maybe birdies. They probably didn't sell many, I can't say I've ever seen one.

[jackhackett]

Something else I thought of, just for the records.... with the different first IF frequency you not only would have to have different IF filters, but the synthesizer would have to generate a different LO frequency, which means the firmware would have to be different as well.

For example, if you were receiving a 454.250 MHz signal, the synthesizer would normally generate a signal 45.1 MHz below that, or 409.150 MHz. For a 45.3 MHz IF it would have to generate 408.950 MHz to receive the same frequency.

I don't think any of the service manuals covers the R series IF radios, at least none that I can find.

[Satelite]

Hello jackhackett:
I wondered about a couple of the above other than the if filters.
I was thinking the if filters would still be fine since still in the same bandwidth radio operated in so ill have to rethink that one.
And I was thinking radio would need a different rss to match a 44.845 crystal over the original 44.645 crystal. ( GM300 series mobile )
My thought was use the normal rss and just enter the freq lower to hopefully hit the correct freq if the other crystal was used.
And I too have not seen the r series in any of my service manuals so it got me to wondering even though I do not nor have I ever seen a r series mobile with the 44.845 crystal.
But it jogged my brain because I recall a Johnson two way radio shop mentioning they had rx problems with a new ford pickup truck years back.
That Johnson mobile radio was a Johnson PPL 6050 mobile which was a vhf at 15 watts and crystal controlled so no rss everything was manually adjusted on that radio.
If I recall they figured the new ford trucks computer also used a 10.7 crystal that the truck had in its computer.
So by changing the crystal they got around it and since the ppl6050 was all manually adjusted for operation I spose they could readjust the filter and calibrate onto the freq they needed since manually done.
I personally cant say since it was shop talk with a Motorola repairman which was me with the Johnson repair tech years back at the Johnson radio store backroom repair bench area.
They liked me at Johnson shop but it cost me 25 cents every time I said Motorola inside that Johnson shop in back with Johnson techs.
Yeppers its considered a cuss word above the F word there :=)
I just dropped 10 bucks in the cuss can when I walked by the front receptionist and she would laugh and give advance warning Erics good for 10 dollars which is 40 M words so count em up guys.
They hate it when I tell them they finally wised up when new owners bought the business and eventually dropped Johnson line and sold the kenwood line but your still the under dog just not lower than whale :o - ooops 25 cents cuss can
I haven't myself had much if any issues that I can recall with a truck or tractor or combine that didn't work fine in rx mode so wasn't really needing any info to solve one like this but just got to thinking.
Still curious for no reason other than wanting to know.
Satelite

[jackhackett]

I was thinking the if filters would still be fine since still in the same bandwidth radio operated in so ill have to rethink that one.
And I was thinking radio would need a different rss to match a 44.845 crystal over the original 44.645 crystal. ( GM300 series mobile )
My thought was use the normal rss and just enter the freq lower to hopefully hit the correct freq if the other crystal was used.

Nope, using the existing IF filters wouldn't work. Mixing 45.1 MHz 1st IF with 44.845 MHz 2nd oscillator would give you 255 KHz, but the radio uses 455 KHz for 2nd IF and discriminator. You'd get no receive at all.

[Satelite]

Hello jackhackett
Well then that solves that now I know so been answered for me.
Thank you for your courteous polite answers.
Satelite

[Max-trac]

The 44.645 xtal is the one that often goes bad from corrosion and makes the receiver go away. You can Transmit near it with a HT on that freq and the receiver comes to life! I believe they had a bad batch of xtals that were soldered with corrosive solder or something. Maxtracs, Radius etc.

[Satelite]

Hello Max-trac
The postings title was a bit misleading but as it was read it then became apparent the 44.645 receive crystal was being compared to a 44.845 rx crystal a ebay seller was selling.
But no mention of a 44.685 MHz crystal in any Motorola repair manual that I and others couldn't find.
Apparently it existed in an r series GM300 is the info I'm hearing.
And I have no repair manual for an R series GM300 mobile soooo ????
So the discussion turned to possibly why one was available but probably wasn't used theories.
Theres a ebay auction number posted above if you wanted to see it and it was that suction that started the qestions in my mind that lead to this posting.
Thank you
Eklb

[Max-trac]

I will have to watch for that, never knew they used a slightly different freq. I have a lot of scrap boards and will watch for the different one(s).
I did order a batch of 10 of the .645 ones to have so I don't have to search for scrap boards.
Thanks!
Keith

[Satelite]

Hello Maxtrac:
Don't think anyone else here saw one either soooo ???
If I'm right the ebay seller was over seas seller so maybe the 44.845 was used out side the usa version gm300 mobiles ????
Have not a clue but we did see the ebay auction that was posted above with them stating Motorola mobiles ??????
Maybe the sellers wrong but picture did clearly show a 44.845 crystal .
Its a head scratcher in wondering out of curiousity thoooo.
Satelite

[RadioRookie]

Satellite, I'm not sure if this will help you, but I found with the newer John Deere equipment that the modem used for their JD Link is constantly transmitting at 3 watts. Which is just enough to interfere with some vhf radios. Specifically in the 150-159 MHz range. I found that disconnecting the modem would get rid of the interference.