Batboard

Hi all,

I have recently inherited a few motorola advisor pagers. These would have to be my favourite pager - big display, easy to use etc.

I need to change the frequency on them. At the moment, most of them are on 148.6375, some are on about 149.8

I have worked out the crystal calculations for them as some use (frx-17.9)/2 and others are (frx-17.9)/3. I have crystals for a few of them so that is fine. The frequency I am moving them to is 148.050.

The problem is, as you may well know, the receiver in these pagers is cycled on and off when waiting for a message, to consume battery power. the pager "wakes up" when it hears the preamble from the transmitter, checks for its capcode and goes back to cycling if the message is not for it.

This cycling of the receiver makes it impossible to tune the receiver as it is on for, maybe 200ms then off for 200ms (approx).. I've been told that there is a point that you can ground that will turn the receiver on all the time, which will make tuning easy. Does anyone know how to do this ??

The other thing I have been told is that you need to change some chip capacitors when changing the frequency (I think its the 5 chip caps that are on the back of the ferrite "antenna")..

I was also hoping that someone might have, or could point me where to get a schematic of the receiver section OR a table showing the capacitors (and values) that I need to change.

Any help with this greatly appreciated.

Thanks,

TLD.

This is a great forum - a credit to everyone here !!

If the pagers are already on 148.6375, changing them to 148.05 isn't a big deal. You won't (and shouldn't) change the chip caps on the ferrite core.

To tune the pager, put the pager in "test mode."

Turn the pager off.
While it's off, press: [Green, Up, Left, Red].
The LED should come on solid. This puts the receiver on all the time for alignment.

With a signal generator, send a high level signal to the pager and align Test point M1 for 455khz. Make sure it's a clean wave on a scope. Adjust the coil next to the crystal for the frequency adjust.

Next, back the signal down until you see the wave on your scope dip in amplitude. Now adjust the remaining coils and trimmer caps for maximum amplitude on the scope, with the LEAST amount of signal. You go back and forth: Maximize the amplitude, back the signal down, repeat until you can no longer max the wave out to the fullest.

Pager is now tuned.

Good luck!
tpg

Thanks for the info, TPG,

I tried the red, up, left, green but nothing happened, no noise, nothing. The red led didnt light. I had fully turned the pager off before doing this.

Do you do each one of these buttons in sequence or all at once ?? It tried both and no go.

Also, I had a look at the receiver board and cant find a point marked "M1" ??

I have all the gear to do the rest of the tuning and I do have a programming cradle and the software.

What am I missing ???

Thanks for your help,

TLD.

oops.. it's Green, Up, Left, Red in sequence....

M1 is the biggest circular solder pad on the board. If you look at the component side of the receiver, you'll see the 2 "box-like" 455khz filters. When you turn the receiver over (trace side), M1 is on the other side of them towards the corner of the board. Use that for your scope and any ground (even the battery neg.)

Let me know.. I have pics too if needed.

tpg

That worked well, thanks !!

So, how far can you move them in frequency before you need to start changing components ?? I have a couple around 148.8 and others at 149.8

I would expect that the 149.8 ones would need component changes ?

tpg, your info and help has been excellent and is greatly appreciated by this little dog !!.

Component changes don't need to be made for at LEAST a 5MHz difference. (in the case of old "plus" series pager receivers.) Anything above 152 should be looked at for component changes in your case. Anything 146-150 should be ok for you.

tpg

Excellent, thanks (again) for the info. I did the re-freq on one of the advisors following your procedure using the 455KHz IF and it worked well. Actually, after the re-freq, the pager would receive a test message from an r1500 code synth connected to an r2600 as a sig gen at a level better than it did on the freq it was originally set for. I got more than a 5dB improvement, and that was only just roughly tuning it.

Its very interesting because all the people I talk to locally say that the advisors are very hard to re-freq, but after doing it, its real easy (as long as you have decent test gear).

I recrystalled a 454Mhz advisor to a different 454 mhz frequency (<300khz away). The "out of area" antenna symbols show up when I power it up so I assume it needs tuning. The above info should help me a lot but is there a diagram anywhere online that shows the location of the pots and stuff I should turn?

Woops I didn't realize the original thread was started in the wrong forum.

Moderator: can you move this to the paging forum?