Technical information
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the deal: Even though all NFM discriminator chips have a SCAN CONTROL pin, Uniden doesn’t always use it!
Some Uniden scanners have a separate Squelch circuit with the SCAN CONTROL pin on the discriminator
unused! You have to find the real Squelch circuit, and then determine the Logic for that circuit. It’s easy, but
differs from one scanner to the next, and I can’t cover them all. I need your help.
See Table 2 below for a good reference. By and large, those with scanners of Uniden origin have
to tackle the preliminaries in this fashion:
1. Locate the NFM Discriminator chip - you will find the Audio pin from Table 1. It remains valid.
2. Determine if the SCAN CONTROL pin on that chip is used. (Follow its trace out on the PCB)
A. If so, then determine the logic order. If the SCAN CONTROL pin is used, then we can use it!
B. If the SCAN CONTROL pin is not used, then locate the real Squelch circuit. The schematic and block
diagrams in the service manual will be helpful. Uniden uses chips like NJM2902, NJM2904 & NJM3403 to
generate Squelch logic. Use your voltmeter to find a spot where the Squelch logic is 0v and 5 or 8v, depending
on the setting of the Squelch control. Table 2 shows details for those Uniden-made scanners with which I am
familiar.
TABLE 2 - UNIDEN SQUELCH CHIPS
Scanner SQ Chip CktSym Pin
PRO-26 NJM3403AV IC-17 14
BC-890XLT NJM2902N IC-8 7
BC-2500XLT NJM3403AV IC-204 14
BC-8500XLT NJM2904M IC-8 7
BC-350A NJM2904S IC-552 8
BC-700A NJM2904D IC-11 7
PRO-51 NJM2902V IC-4 8
PRO-2030 NJM2904S IC-10 8
Computer Controlled Scanning with Optoelectronic’s OptoScan and Probe V3
by Perry Joseph
My thanks to all who took the time to review Probe V3.0 in the last issue of "The Urban DX’er". Special thanks
to Bob Kozlarek for inviting me to provide some feedback on that review and to provide additional notes on the
OptoScan and Probe V3.
First let me provide some background on myself. I am 43 years old and live in St. Louis, Missouri. I have been
developing software for about 10 years. The bulk of my work is for small companies and focuses primarily on
database management and support. Long before my involvement in software development, and before the
introduction of the personal computer, I have enjoyed the hobby of "scanning" starting with an early Bearcat
crystal controlled radio. My primary pleasure is listening to public safety. I also have a ham license and enjoy
talking with friends on the 2 meter band. I belong to a local scanner club in St. Louis called SABRE (St. Louis
All Band Radio Enthusiasts) and am the volunteer Editor for our newsletter, appropriately named "SABRE
News".
Over the years, there have been a few milestones in my hobby of scanning. The first major milestone for me
was the introduction of programmable scanners. What a delight that was; no more having to procure, install
and swap crystals! The next major milestone was the introduction of the personal computer. Instead of having
to keep copious hand written notes of frequencies and users, I could keep my volume of notes organized in a
database program. I have always considered scanning to be a data driven hobby and the marriage of