A lot of interest has been generated about how to 'hook up' your scanner in order to receive and demodulate POCSAG (Pager Alphanumeric Codes).
In order to do this it is a MUST to supply 'clean audio' to the interface. Most scanners 'filter' the audio before it gets to the speaker, causing much of the needed low frequencies to be removed. This is usually why you cannot 'get anything' when you use some interfaces with PD203, Cylex etc. The best place to 'take off' the audio is at the "FM Descriminator" chip, where the Frequency Modulated (FM) audio is demodulated into AM Amplitude Modulated audio.
Most people use the small 'test lead 'push type' grippers to clip onto the appropriate leg. and bring that out to a chasis mount RCA female jack.
Below is a LONG LIST we found on the net,and contains many of the most common "FM DEscriminator Chips" and what leg to 'tap off of' If your model is not listed, the chip numbers are usually printed on top, so you can still identify most of them.
CKT RF-in SCAN AUDIO
SCANNER NFM CHIP TYPE SYMBOL Pin Pin BASEBAND
=============== =============== ======= ===== ===== =========
MPS5071 n/a 16 13 9
AR-1000 TA-7787AF IC-4 16 none 9
AR-2002 MC-3357P IC-4 16 13 9
AR-2500 TA-7761P IC-13 16 9
AR-3000 MC-3357P ? 16 13 9
AR-800 MC-3361N IC-200 16 13 9
AR-900 MC-3361N IC-201 16 13 9
AR-950 MC-3361N IC-201 16 13 9
AR-8000 NFM TK10489M or-85M U1 20 16-17 11
AR-8000 WFM/AM TA7792F U3 16 - 8
BC-100XL MC-3359P IC-1 18 15 10
BC-100XLT TK-10421M-2 IC-401 20 16 11
BC-140XLT MC-3359P IC-1 18 15 10 *
BC-200XLT TK-10421M-2 IC-401 20 16 11
BC-205XLT TK-10421M-2 IC-401 20 16 11
BC-250 ? IC-3 16 13 9
BC-2500XLT TK-10930VTL IC-201 24 - 12-FM 13-AM
BC-3000 NFM/AM TK-10930V IC-202 24 - 12-NFM 13-AM
BC-3000 WFM TK-10489M IC-203 20 16-17 11
BC-350A NJM-3359D-A IC-3 18 15 10
BC-400XLT NJM-3359D-A IC-1 18 15 10
BC-560XLT NJM-3359D-A IC-1 18 15 10
BC-700A NJM-3359D-A IC-3 18 15 10
BC-760XLT NJM-3359D-A IC-2 18 15 10
BC-800XLT MC-3359P IC-1 18 15 10
BC-8500XLT MC-3361BP IC-9 16 13 9
BC-855XLT TK-10421M-2 IC-401 20 16 11
BC-890XLT NJM-3359D-A IC-3 18 15 10
BC-950XLT NJM-3359D-A IC-2 18 15 10
HX-1000 TK-10420 U-201 16 13 9
MR-8100 NJM-3359D-A IC-3 18 15 10
MX-5000 MC-3357P IC-4 16 13 9
MX-7000 MC-3357P IC-4 16 13 9
PRO-2002 MC-3357P IC-101 16 13 9
PRO-2003 MC-3357P IC-104 16 13 9
PRO-2004 NFM/AM TK-10420 IC-2 16 13 9 (TP4)
PRO-2004 WFM KB4419A IC-1 1 - 6 (TP3)
PRO-2005 NFM/AM TK-10420 IC-2 16 13 9 (TP2)
PRO-2005 WFM KA2243N/HA12413 IC-1 1 - 10 (TP1)
PRO-2006 NFM/AM TK-10420 IC-2 16 13 9 (TP2)
PRO-2006 WFM KA2243N/HA12413 IC-1 1 - 10 (TP1)
PRO-2011 TK-10420 IC-1 16 13 9
PRO-2020 MC-3357P IC-101 16 13 9
PRO-2021 TK-10420 IC-2 16 13 9
PRO-2022 MC-3361N IC-1 16 13 9
PRO-2023 NJM-3359D-A ? 18 15 10
PRO-2024 MC-3361N IC-2 16 13 9
PRO-2025 NJM-3359D-A IC-1 18 15 10
PRO-2026 NJM-3359D-A IC-7 18 15 10
PRO-2027 MC-3361N IC-2 16 13 9
PRO-2028 NJM-3359D-A IC-2 18 15 10
PRO-2030 NJM-3359D-A IC-3 18 15 10
PRO-2035 NFM/AM TK-10420 IC-2 16 13 9 (TP2)
PRO-2035 WFM KA2243N/HA12413 IC-1 1 - 10 (TP1)
PRO-2042 NFM/AM TK-10420 IC-2 16 13 9 (TP2)
PRO-2042 WFM KA2243N/HA12413 IC-1 1 - 10 (TP1)
PRO-23 MC-3361BD IC-1 16 13 9
PRO-26 NFM/AM TK-10930V IC-14 24 - 12-NFM 13-AM
PRO-26 WFM TK-10489M IC-16 20 16-17 11
PRO-31 TK-10420 IC-1 16 13 9
PRO-32 TK-10420 IC-101 16 13 9
PRO-34 TK-10420 IC-101 16 13 9
PRO-35 TK-10421M-2 IC-401 20 16 11
PRO-36 TK-10420 IC-101 16 13 9
PRO-37 TK-10420 IC-101 16 13 9 (TP103)
PRO-38 MC-3359P IC-1 18 15 10
PRO-39 MC-3361N IC-201 16 13 9
PRO-41 MC-3359P IC-1 18 15 10
PRO-42 MC-3361N IC-2 16 13 9
PRO-43 TK-10427/-10420 IC-301 16 13 9
PRO-44 MC-3361N IC-201 16 13 9
PRO-46 TK-10421M-3LT IC-401 20 16 11
PRO-51 MC-3361BD IC-1 16 13 9
PRO-60 ? IC-301 16 13 9
Icom R-1 NFM TK-10487 DET-A IC-1 20 Q1 11
Icom R-1 WFM TA-7787AF DET-B IC-1 16 7 9
Icom R7100 Said to be "top of R230 on the top of main PCB" *
R-1600 NJM-3359D-A IC-2 18 15 10
R-4030 TK-10421M-2 IC-401 20 16 11
SR-15 TK-10421D-2 IC-1 16 13 9
StandardCCR708A TK-10420D Q602 16 13 9 *
TurboScan 2 3130-6056-502 U-201 18 ? 10 or 16
Yaesu FRG-9600 MC-3357P ? 16 13 9 *
====================================================================
* Not personally verified
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 we are familiar.
TABLE 2
UNIDEN SQUELCH CHIPS
Updated 4/08/96
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