That is VR4 inside the scanner. It is marked on the circuit board. The frequency drift prevented the scanner from decoding transmissions on 800 MHz P25 trunked systems. I imagine it could have the same effect on UHF P25 conventional frequencies if the oscillator drifted far enough.
Hello KevinC, and yes. i have read about it. Will the VR4 cause the frequency issue? on it’s mainly for the 800 mhz as tvengr stated? i don’t used the 800 mhz in Los Angeles area.. mainly 400-500 mhz and some 120 mhz. Thank you guys for your time and guidance.
Is that system P25 digital? So the P25 ability for the Pro96 and Pro2096 were enhanced with the progression of firmware. 1.1 won't cut it. I remember the last two version of firmware 1.3 and 1.4 here in Chi-RAQ-land made things a lot better. You should go into the Wiki section here on RRef and download the 1.4 that is provided. Of course you need a special cable to upload to the Scanner and I found that ARC96 software was far better at that than the old Win96 stuff. As far as hearing it on one channel? The scanner works (Trunking) off of the Control Channels listed in the Database for that System. There's usually 3 or 4 or more? if It's CA listed in RED that need to be entered. Also the MODE needs to be MOT or the correct System. The manual and downloads are here ... Pro-96 - The RadioReference Wiki
These are P25 conventional frequencies the OP is trying to receive. There are no control channels involved. The frequencies are about 6.25 KHz off from what they should be. I suspect that the master oscillator has drifted off frequency. Crystals can change frequency as they age. I have needed to replace quite a few in radio microphone transmitters and receivers. The VR4 adjustment in the scanner may be able to compensate for that. Frequency is critical for decoding P25 signals.
The frequency of the master oscillator crystal has probably drifted. Frequency is critical for decoding P25 transmissions. You most likely need to set the receiver to a different frequency to compensate for the frequency drift. Set your scanner to 506.73750. Remove the covers. VR4 is marked on the circuit board. Make a note of the current setting for VR4. If I remember correctly, you may need a couple of clip leads to connect the battery case to the scanner with the covers removed. Slowly adjust VR4 to see if you are able to receive Central Dispatch with the scanner set to the correct frequency. I programmed a PRO-96 for a Harford County MD volunteer firefighter and did a complete alignment using professional test equipment. It would not receive the Baltimore County MD P25 system until I adjusted VR4.
thank you so much for your guidance. so i did as you told me but it didn’t make any difference. Can it be the version i have since its the 1st version V1.1 and i know they have V1.3 and V1.4 i believe. i just need to find it so i can updated and maybe that way it might work adjusting the VR4.
