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1991-01-06
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Item 9175111 90/12/16 14:49
From: R.SANDERS15 Robert E. Sanders
To: NA5E Larry L. Ledlow
Sub: DataSquelch info
Here's the file on Bill Cheek's DataSquelch for Pro-2004/5/6 radios:
Bill Cheek
COMMTRONICS ENGINEERING - Communications & Information
PO BOX 262478, San Diego, CA 92196
November 23, 1990; 4:54 pm
=================================================================
DATA/TONE SQUELCH CIRCUIT FOR THE PRO-2004, PRO-2005 & PRO-2006
=================================================================
Here's an easy modification to make PRO-2004/5/6 scanners
recognize worthless DATA and/or continuous TONE signals and to
resume SCANning or SEARCHing within a second after locking up on
these types of signals. It works similar to the SOUND SQUELCH
which responds to silent or unmodulated carriers. In fact, the
DATA SQUELCH works with the SOUND SQUELCH, but is independent of
it except for the SOUND SQUELCH button on the front panel which
activates or deactivates both functions. Construction and
installation are simple and within the ability of most hobbyists.
The DATA SQUELCH is ideal for use when SCANning or SEARCHing
trunked channels! No longer do trunked data channels have to be
locked out! (They change every day, anyway.) The scanner skips
over those obnoxious signals! It will also discriminate against
cellular data and most FBI-type continuous tones. My DATA SQUELCH
will likewise discriminate against continuous tones used on the
Improved Mobile Telephone Service (IMTS) and other non-voice
signals including digital pagers. In other words, the DATA
SQUELCH accepts voice signals and rejects most others.
STRONG ADVICE: You should have the Service Manual for your
scanner before doing this modification. Order it from any Radio
Shack store or directly from Tandy National Parts Center in Ft.
Worth, Tx; (800) 442-2425.
CONSTRUCTION OF THE DATA SQUELCH CIRCUIT BOARD
================================================
Cut a piece of "perf board" about 1" x 1" though smaller is ok if
you are good at micro circuits. Refer to the Parts List and, if
available, the Schematic Diagram:
DIRECTIONS FOR PRO-2004/5/6: Directly to Pin 5 of U-1, solder
the (+) leg of C-2 and one leg of each of R-1 and R-2. Ground
the free ends of C-2 and R-2. To the free end of R-1, solder the
cathode of one of the diodes, D-2. To the anode of D-2, solder
the cathode of D-1. Ground the anode of D-1. NOTE: the junction
of D-1 cathode and D-2 anode will be the INPUT of this circuit.
To Pin 2 of U-1, solder one end of R-3 and the anode of D-3.
Solder the free end of R-3 to Pin 3 of U-1. Solder a hookup wire
several inches long to the cathode of D-3 & let hang free.
Solder a several inch long hookup wire to Pin 3 of U-1 & let hang
free. Ground Pin 12 of U-1. Solder one end terminal of VR-1 to
Pin 3 of U-1; solder the other end terminal of VR-1 to ground.
Solder the middle lug of VR-1 to Pin 4 of U-1. Pins
1,6,7,8,9,10,11,13 & 14 of U-1 are not used.
PRO-2004 ONLY: Solder the (+) leg of C-1 directly to IC-5, Pin
14.
PRO-2005/6 ONLY: Solder the (+) leg of C-1 directly to IC-5, Pin
7.
PRO-2004/5/6 ALL: Solder a hookup wire to the (-) leg of C-1.
Solder the other end of this hookup wire to the INPUT of the
above circuit at the junction of D-1 and D-2. Solder the ground
trace of the new circuit board to a ground in the scanner.
Solder the free end of the hookup wire at Pin 3 of U-1 to the
OUTPUT leg of IC-8, the +5v supply regulator on the main chassis
of the scanner. IC-8 is the same in all three scanners,
PRO-2004/5/6.
PRO-2004 ONLY: Locate CN-504 on the Logic/CPU Board, PC-3, and
follow its wire bundle back to the main receiver board. Locate
the sky blue (light blue) wire that connects to the chassis at
the right end of the row of wires and remove that wire from the
chassis. (This wire comes from Pin 15 of CN-504.) Solder the
anode of D-4 to the spot where the blue wire was removed. Solder
the now loose blue wire to the cathode of D-4. Solder the free
end of the hookup wire at the cathode of D-3 to the cathode of
D-4.
PRO-2005/6 ONLY: Locate CN-3 on the main receiver Board and
follow its wire bundle up to the Logic/CPU board. Locate the sky
blue (light blue) wire that connects to Pin 4 of CN-3. Clip that
blue wire halfway between CN-3 and the Logic/CPU Board. Solder
the anode of D-4 to the loose end of the blue wire that goes down
to CN-3. Solder the cathode of D-4 to the loose end of the blue
wire that goes up to the Logic/CPU Board. Solder the free end of
the hookup wire from D-3 to the cathode of D-4.
PRO-2004/5/6 ALL: ADJUSTMENT OF VR-1: Push the SOUND SQUELCH
button ON and attach a voltmeter (-) to ground and (+) to Pin 5
of U-1. Tune the scanner to a strong, noisy data channel or to a
loud, single tone carrier. Measure the DC voltage at Pin 5 of
U-1, (2.5v to 4.5v, typically). Calculate 80% of that
measurement, and adjust VR-1 for the 80% level of the above
measurement. Typically, about 2 to 3.8v. The exact adjustment
isn't too critical, but if set too low, then voice signals will
trigger the SCAN/SEARCH RESUME. If set too high, then data &
tone signals won't trigger the SCAN/SEARCH RESUME. Another way
to find the optimum setting is to put a voltmeter (+) on Pin 2 of
U-1 and (-) to ground and tune the scanner to a cellular or
trunked data channel. Adjust VR-1, first one way and then the
other and then to a point so that the voltage on Pin 2 of U-1
just becomes stable with a nice and steady +5 volts. It takes a
steady 5-volts for about one second to trigger the SCAN/SEARCH
RESUME function, but don't adjust VR-1 any further than necessary
to stabilize the DATA/TONE voltage at Pin 2.
OPERATION & NOTES: The description for the above circuit does
not discuss the DPDT switch shown in the schematic diagram, and
which can be wired as shown to select SOUND SQUELCH only or both
SOUND and DATA SQUELCH, combined. More sophisticated switching
schemes can be devised to select one or the other or both. As it
is, the above described basic circuit runs BOTH SOUND & DATA
SQUELCH at the same time. That is, your scanner will resume
SCANning or SEARCHing almost immediately after it locks up on
either a silent signal or a data/continuous tone signal! Voice
signals will cause the scanner to stay locked as normal until the
signal goes away. Minor adjustment of VR-1 may be necessary for
optimum results, but the final setting will produce a voltage on
Pin 4 of U-1 of about 80% of the peak voltage on Pin 5 of U-1.
The DC input signal at Pin 5 of U-1 will be nearly zero on silent
or quiet signals and about 2.8 to 4.5v with data & continuous
tone signals. Pin 5 will show a very erratic and rapidly
changing voltage from nearly zero to 4 volts or so for voice
signals. The DC output voltage at Pin 2 of U-1 will be nearly
zero on silent or quiet signals; and a steady +5v with data &
continuous tone signals. Voice signals will cause a rapid
fluctuation of the signal between 0-5 volts at Pin 2 of U-1.
When the SOUND SQUELCH button is off, neither SOUND nor DATA
SQUELCH are operable and scanner operation will be completely
normal.
IN CASE OF DIFFICULTY: The most critical part of this mod is the
rectifier circuit consisting of D-1, D-2, R-1, R-2, C-1 and C-2.
Make sure the diode polarities are correct (banded end is the
cathode). Make sure polarity of the capacitors is correct. Tune
the scanner to a strong cellular (879-881 MHz) or trunked data
channel (851-866 MHz), and measure the DC voltage at Pin 5 of
U-1. There should be between 2.5 and 4.5 volts. You won't
measure "too much" but not enough is possible. If so, check the
wiring and components mentioned just above. Next most critical
is the polarity and wiring of the two isolation diodes, D-3 and
D-4. Last but not least is the wiring of U-1. The circuit is so
simple and affirmative in its action that you're not likely to
encounter trouble if you follow these instructions. On one
PRO-2005, I noticed a chirping, morse code type of sound on quiet
channels. If yours exhibits this, change capacitor C-1 from
1.0-uF to 0.1-uF, #272-1432. If the "tweet" is still there, then
solder a 220-uF (or larger) capacitor directly to Pins 4 and 11
of IC-5 in the scanner. Pin 4 should get the (+) lug of the
capacitor while Pin 11 will be (-). Radio Shack part number for
the capacitor is #272-1029.
If you can't resolve a problem, send me a SASE and one loose
extra stamp with a complete description of the problem and its
symptoms and I'll respond with written suggestions and advice.
Sorry, no phone calls, please.
THEORY OF OPERATION OF THE DATA/TONE SQUELCH
=============================================
To understand the simple operation of my DATA SQUELCH, it is
first necessary to understand the PRO-2004/5/6's SOUND SQUELCH
(SSQ) circuit on which we will "piggy back" the new DATA SQUELCH
circuit. The circuits are identical among the PRO-2004/5/6
scanners but circuit symbols differ. Bear with me here while I
use a simple scheme for this discussion. P4 means PRO-2004; P5/6
means PRO-2005 and PRO-2006 and P4/5/6 means "all".
SOUND SQUELCH THEORY OF OPERATION: A weak portion of the
receiver's audio is sampled at the detector and amplified through
IC-5 (P4/5/6). The highly amplified audio is fed from IC5, (P4,
Pin 14 or P5/6, Pin 7) to a rectifier network (P4, D-41 & D-42;
P5/6, D-43 & D-44). This rectifier network converts the audio
signal to a DC signal that is proportional in level to the level
of the audio signal, and it is used simply as a bias to turn on
or off a transistor, (P4, Q-21; P5/6, Q-19). Most audio signals
are strong enough to turn the transistor on while very weak or
silent signals keep it off. When the transistor is off, 5-volts
is on its collector, but when the transistor is ON, the collector
drops to nearly zero volts. 5 volts and 0 volts forms the logic
required by the CPU for making decisions. The collector of the
transistor is fed directly to the CPU, (P4, IC-503, Pin 24; P5/6,
IC-501, Pin 18). When the SOUND SQUELCH button on the front
panel is set to the ON position and when CPU's SSQ pin is at zero
volts, the scanner scans or searches as normal, locking on any
signals which break the squelch. Similarly, when the SOUND
SQUELCH button is off, a ground is placed on the CPU's SSQ pin,
which keeps it at zero volts, no matter what.
When the SOUND SQUELCH button is on, and when the scanner
encounters a silent or unmodulated carrier, then the transistor
discussed above gets turned off and a 5-volt level on its
collector is fed to the CPU's SSQ pin. A 5-volt signal on the
CPU's SSQ pin makes the scanner resume scanning within a second
after locking onto a carrier. Therefore, as long as there are
voices or other audio signals present, the CPU's SSQ pin will be
"0-v low" and operation is normal. When that pin goes "+5v
high", the CPU is programmed to resume scanning or searching.
DATA SQUELCH THEORY OF OPERATION: Since the CPU's SSQ pin
responds only to low and high logic and really doesn't know the
difference between voice and data, we can use this function with
a separate circuit to make it discriminate against continuous
tones and data in the same way it discriminates against silent
carriers. All we need is a circuit that sends a "high" to the
CPU's SSQ pin in the presence of strong, sustained audio signals
such as data or continuous tones. My circuit does this handily
since voice signals are erratic, varying, and not at all like
data or continuous tones. C-1 of our circuit samples the
amplified audio and passes it to a new rectifier circuit, D-1 and
D-2, which with R-1, R-2 and C-2, becomes a DC signal
proportional to the level of the audio signal. This DC signal is
fed to Pin 5 of U-1, a Voltage Comparator IC. A reference
voltage is adjusted by VR-1 and fed to Pin 4 of U-1. As long as
the DC signal at Pin 5 is less than the reference signal at Pin
4, the output of U-1 at Pin 2 will be zero volts "low". When the
DC signal at Pin 5 exceeds the reference voltage at Pin 4, then
the output of U-1 goes to +5v "high" at Pin 2.
The output of U-1, Pin 2 is coupled to the CPU via isolation
diode, D-3. A "high" will tell the CPU to make the scanner
resume SCANning or SEARCHing while a "low" does nothing unusual.
When VR-1 is correctly adjusted, the output of U-1, Pin 2 will
never go "high" long enough to trigger the CPU unless data or
continuous tones are present. Voice signals may make U-1's
output go high momentarily, but the interval will not be long
enough to trigger the CPU, because a duration of about .5 to 1
second is required before the CPU will trigger. Therefore, most
voice signals of interest will not send a "high" to the CPU, but
continuous tones and data will! Therefore, our DATA SQUELCH works
exactly like, though inversely to, the SOUND SQUELCH.
Isolation diodes, D-3 and D-4, allow the SOUND SQUELCH and the
DATA SQUELCH to work simultaneously and not interfere with each
other. Both silent and data/tone signals will cause the scanner
to resume SCANning or SEARCHing, but voice signals will not be
affected by the SOUND or DATA SQUELCH!
WRAPUP: Sometimes, natural pauses of a second or more in speech
signals will be interpreted by the SOUND SQUELCH as a silent
signal. SCAN or SEARCH may resume before speech begins after the
pause. It is, therefore, ideal to route the SOUND SQUELCH and
DATA SQUELCH functions through an external selector switch to
permit selection of one, the other or both functions for special
monitoring situations. Two toggle switches or a cumbersome
rotary switch are required to do this. Next to ideal is a simple
DPDT toggle switch, which when wired as shown in the schematic
diagram, will select both DATA and SOUND SQUELCH simultaneously,
or DATA SQUELCH only.
PARTS LIST FOR DATA/TONE SQUELCH CIRCUIT
===========================================
Circuit
Symbol Quan Description with Radio Shack part numbers
======= ==== ==========================================
C-1 1 1-uF/35vdc #272-1434 (See Text)
C-2 1 2.2-uF/35vdc #272-1435
D-1,2,3,4 4 1N4148 Switching diodes; #276-1122
J-1 1 IC Socket, 14-pin DIP, for U-1 below; #276-1999
R-1 1 390-ohm; #271-018
R-2 1 12,000-ohm; non-Radio Shack, but a 10-k and a
2.2k can be wired in series to make the needed
12-k resistor; use one each of RS #271-1335 and
271-1325 if need be.
R-3 1 3,300-ohm; #271-1328
S-1 1 DPDT toggle switch, for optional control;
#275-626
U-1 1 LM-339 Comparator; #276-1712
VR-1 1 10,000-ohm trim pot; #271-282
Misc Perf board; #276-1395
Misc Hookup wire; #278-776; Salvage the inner wires
for hookups
SCHEMATIC DIAGRAM FOR DATA/TONE SQUELCH CIRCUIT
===============================================
Since you copied this file from a BBS, there is no way a
schematic diagram can be reliably conveyed. You may not need
one, as detailed as this is, but if you do, send a #10 Self
Addressed Stamped Envelope and four (4) loose, extra first class
postage stamps for the schematic and a printed copy of this
manuscript. This offer expires January 31, 1991, after which a
nominal charge will apply.
=================================================================
COMMTRONICS ENGINEERING PO BOX 262478 SAN DIEG0, CA 92196
=================================================================
There it is... hope you find it useful.
----------