We have a customer with Minitor 3's and 4's on 153.215 MHz. In the standard M3/M4 configuration, there is a very strong birdie on that frequency which greatly reduces the effective range of the pager. It turns out that this frequency is the 38th harmonic of the 4.032 MHz clock oscillator on the decoder board. It sounds like an open carrier on frequency.
After having returned a few units to Moto for repair (at $73 a copy!) I figured out how to fix them myself. The clock crystal is a small, cylindrical can near the top of the decoder board. It stands up from the board in a silicone cushion. Replace it with the 4.000 MHz crystal from a P10/P50 portable PL board, 4805664G34. Then you need to use the Windows PPS in the engineering mode: http://batboard.batlabs.com/viewtopic.php?t=45816
In the lower, left-hand corner of the Engineering Data screen, change the Xtal: to 4.000 MHz. Click OK and program the pager. Power cycle and re-read the pager. Change the tone system on the User Data screen to User. Do NOT use Motorola, GE, Plectron, etc. Enter the tone frequencies directly in the Channel screens. They will probably change to something close to your tone frequencies, but not exact. That shouldn't be a problem and they'll generally work fine. Program the pager, power cycle and test it. The birdie should be gone!
How to fix Minitor 3/4 spurs or birdies
Moderator: Queue Moderator
