Minitor II VHF to 2m Ham Band?

n5api · Post by **n5api** » Sun Jul 23, 2006 3:18 pm

Hi everyone. I have been given an opportunity to buy some used Minitor II VHF pagers at a very good price. My local ARES group would like to re-crystal them for our 2 meter repeater. The repeater controller has the ability to do 2-tone encoding, and we would set it up to send out tones when the repeater is placed in ARES mode. Which brings me to my question...

Are the VHF Hi Minitor II receivers broad-banded enough to be moved onto the 2m Ham band (specifically 146.92Mhz)? I did a search and found a post regarding UHF Minitor IIs, but not VHF. I'd assume that they'd make the trip without any modification other than just re-crystal and re-tune, but you know what they say about assuming something.

If anyone knows, and/or has tried to move these down to the Ham band, I'd love to hear from them.

Thanks,
John, N5API

n5api · Post by **n5api** » Fri Jul 28, 2006 10:30 am

Nobody knows if these pagers will go into the Ham bands or not?! I can't believe I've stumped the BatBoards!

WB2IID · Post by **WB2IID** » Sun Jul 30, 2006 1:20 pm

A few thoughts:

What frequency are the pagers on currently?

It would be helpful if you had a service manual for the VHF pager, that would give you some clue as to frequency split. The closer the current frequency is to the 2M band, the better.

But as a general rule it's easier to go down in frequency rather than up. Meaning that you can add capacitance into the circuit easier than taking it out. There's probably 4 to 6 components (capacitors) that would have to change. The antenna would not have to change.

Assuming the frequency coverage is split up i 150-162 and 162-174 MHz, and if you have a high split VHF pager, you could get low split RF decks for them and have an easier time tuning them up. I have converted a VHF M2 to low band just by changing the RF deck.

I would go ahead and get one, crystal it up and see how it does.

Joe

n5api · Post by **n5api** » Sun Jul 30, 2006 4:40 pm

Thanks Joe for the reply.

They are currently on 154.xxx (805 I think, I don't have them in front of me right now.) Like you said, I figured I'd grab one or two for now, and see if I could get them to work.

I guess I should start looking on eBay for a service manual, unless someone on here can give me instructions on how to tune these. I've done a search on the boards here, and haven't found anything. The BatLabs Minitor page seems to be lacking the info as well, or did I miss something?

73,
John N5API

WB2IID · Post by **WB2IID** » Sun Jul 30, 2006 5:23 pm

The alignment procedure is not all that complicated. The only adjustments are on the RF deck and consist of tuning capacitors and variable inductors.

I'm more familiar with the low band, which have 3 caps and 3 inductors. Going from memory, one cap is the antenna adjustment, one for a channel 2 antenna tweak and the other is for the 1st IF match to the crystal filter. Two inductors are near the antenna trimer ant the other is next to the crystal.

If you look at the component side of the main circuit board you will notice a small circuit board mounted at right angles to the main board - this is the low IF assembly. On its top edge you will see a metal foil area on its edge - this is a 455 KHz test point.

So the alignment procedure is:

Connect RF voltmeter to test point. While receiving an on channel signal, peak the antenna trimmer and the two nearby inductors for max on the rf voltmeter. Peak the other trimmer cap nearest to the test point. You might have to reduce the input signal to keep the test point output from limiting.

To adjust the crystal, you can tune it for 455.000 KHz on a frequency counter with an on-channel signal of known accuracy.

That's about it - except if you really want to optimize the pager for very weak signal 2-tone decoding, in which case I tune the crystal and crystal filter adjustments for reliable alerting with really noisy tone transmissions.

ICEMANTIM · Post by **ICEMANTIM** » Mon Oct 30, 2006 7:16 pm

Hello We have done about 15 of the Minitor 2 pagers. Ours where on 154.415 and we had them return a crystaled to 146.835. There is a guy from New York that done ours. He charges $27.00 per pager. Ours work great. If you need the web site PM me and i will send it to you.

n5api · Post by **n5api** » Thu Nov 02, 2006 3:06 pm

Thanks for all the info and suggestions. I have successfully converted one pager to the Ham band, and another two will follow shortly. I will post all the tips and tricks I have discovered during the process once the project is done.

John, N5API