Cellular restoration
To restore the missing CMT frequencies, merely clip diode D502.
It is located in the upper left corner of the CPU/display board.
-------
To enable the Radio Shack PRO-2006 scanner to monitor the cellular phone
frequencies (870.030-879.360 System A Base) (880.650-889.980 System B Base)
and the actual mobile telephone frequency (825.030-834.360 System A Mobile)
and (835.650-844.980 System B Mobile) do the following:
1. Remove the top cover only. It is held by the 2 screws on back.
2. Looking behind the metal plate covering the front panel, look at your
left top corner. You will see 2 glass diodes sticking out of the PC
board (PC-3). The one at the bottom is labeled D502.
3. Simply cut the lead on the diode (D502).
Turn the radio on and program the limit search memories with the ranges
indicated on top. The System A and B Base are the ones to listen to. The
reason is that you'll be able to hear both sides of the conversation. If
you try listening the Mobile signal, you'll only hear the signal being sent
out by the actual phone. Also the signal on the cellular phone is only a
measly 4 watts.
This mod is so simple, you can do it in less than 3 minutes. Only a small
cutting plier is needed, as well as the screwdriver.
Scan rate increase
Replace CX503 (12Mhz) with a 16Mhz crystal, clip diode D503 (near D502)
The unit now scans at around 40 channels per second.
Squelch hysteresis suppression
Parts : 100-200K ohm 1/8w resistor
Locate R152 (33K) on the linear PCB (main board). This is a tricky
resistor to get to, since it is on the bottom side of the board.
Remove this resistor, and replace it with a 100-200K resistor. The
higher the resistance, the less hysteresis will be present. I found
100K gave me all the razor-sharpness I was looking for, without
sacrificing performance.
"S" meter output
Parts : 10Kohm 1/8w resistor, 0.1 uf capacitor
Locate D33 on the linear PCB. Solder in the 10K resistor to the ANODE
of this diode. Note this is not the same as TP2. Connect a wire from
the free end of this resistor to a rear panel jack (RCA). Solder the
0.1uf capacitor from the jack's center terminal to ground. Output on
this jack follows the AGC voltage. Negative for no signal, goes
positive when a signal is present, increasing with signal strength.
A 1Volt full scale panel meter makes a good "S" meter
--------
Much more detailed information with ascii schematic
Increased headphone audio
Locate resistor R228 (27 ohm) on linear board (near IC7).
Remove this resistor and replace it with a jumper wire.
6400 channel memory capacity (ADVANCED TECHNICIANS ONLY!)
Parts : Hitachi HM62256LFP-12 (256Kx8 SRAM) or equivalent (flat pack required)
4 Position DIP-switch
10KOhm resistor SIP (or 4 10K 1/8w resistors)
This modification is complicated, so don't try it if you're not fully
sure of your ability.
1) Remove front panel from scanner, disconnect wiring harnesses.
You will lose all current programs (Sorry!)
2) Remove metal shield from panel CAREFULLY!
Remove screws holding CPU board in front panel.
Carefully separate CPU board from keyboard.
3) Locate IC505 next to CPU and remove it from the board.
Notice this is a 24-pin IC, and that there are 4 extra pads
to the top of pin 1. All pin numbers given hereafter will
refer to the new 28 pin IC, with pin 4 being the old IC's
pin 1. Follow me? The pads for the new IC are already present.
4) To adapt to the new RAM, a few traces must be sliced.
A) Slice the trace connecting pin 28 to pin 26
B) Slice trace connecting pin 27 to pin 23 (bottom of board)
C) Slice trace connecting pin 2 to ground (bottom of board)
5) Install the new RAM, and connect a jumper from CPU IC501
pin 67 (+5V) to pin 28 of the new RAM.
6) To address the extended memory, external switches must be added
and connected to the unused address lines of the new RAM.
Just how you implement this is up to you. Regardless of how you
do it, you will need to connect a wire bundle from the new RAM
pins 1,2,23,26 to the outside world. I mounted a jack on the rear
panel into which a 4 position dip-switch can be mounted.
7) Add pull-up resistors from new address lines to +5V, available at
pin 3 of the +5V regulator IC8.
8) Reassemble unit, installing all shields and ground straps.
9) Testing & checkout
A) With all switches 'OFF' enter '1000.000' into memory channel 1.
B) Toggle switch 1 to on and return to channel 1. Enter '1001.000'
C) Repeat for all switch combinations. Lockout channel 1 in each
of the 16 memory blocks. You now have a coded channel to key
you in on which block you're scanning.
D) Enjoy 6400 channels of pure scanning power!
You now have:
16 Blocks of 400 memory channels per block
160 Search ranges (10 per block)
160 Temporary scratchpad channels (10 per block)
Notice that custom settings (delay/mode) are unique to EACH
channel, but priority and speed are common to all blocks.
You might dedicate a common channel in each block to be the
priority channel.
Improving Audio
The Realistic PRO-2005/6 scanners are considered by listeners to be one of the finest scanning receivers available. These units cover 25-1300 MHz in AM, narrow-FM, and wide-FM modes with only a single break in coverage from 520-760 MHz. All this was packaged for under $400, (and under $300 when they were finally discontinued by Radio Shack.) There is one major fault with these receivers: The audio fidelity is very poor. The designers did a great job in the RF sections of the receiver, but must have slept through the audio design! Scanners are not supposed to be hi-fi receivers; however, their audio performance should be at least as good as a common amateur transceiver. The author compared the audio of the PRO-2006 with that of the Kenwood TM-2550 transceiver. Even when the '2006 was connected to a good-quality external speaker, the audio was miserable. The culprit: Several coupling and bypass capacitors in the audio section have been miscalculated by the designers. Making the component changes suggested below will dramatically increase the audio quality of the PRO-2005 and 2006 scanners. These two units are virtually identical (The main difference is that the LCD backlight can not be dimmed on the '2006. It can only be be turned ON or OFF.) Be aware that alterations to your scanner might void any warranty left, and if not carefully done, can be hazardous to its health. Any work on these units should be done at a static-free workstation, if possible. THE AUTHOR ASSUMES NO LIABILITY FOR THE INFORMATION CONTAINED HEREIN! All the suggested changes are on the left-rear corner of the LINEAR circuit board, which is located on top of the scanner. These changes can be made without removing the board, but it is much easier to remove it. Be careful when re-installing the board; there is a hidden connector on the bottom of the LINEAR board that must be lined up with the PLL board underneath. The following changes will improve the speaker and headphone audio. If you're using an external speaker, you'll be very pleasantly surprised by the results:
| Component Designator | Old Value | New Value | Comment |
| C226 | 100 uF | 1000_uF | Helps bass response |
| C211 | 6.8 nF | 0.1 uF | " " |
| C206 | 47 nF | 0.47 uF | " " |
| C207 | 56 nF | 0.47 uF | " " |
| C204 | 10 nF | 4.7 uF | RF/AF bypass. Original part is surface-mounted on PCB. DO NOT REMOVE ORIGINAL. New C204 is soldered on TOP of IC5. Watch polarity: Cap (+) to pin 3 of IC5 Cap (-) to pin 11 of IC5 |
| C208 | 4.7 nF | 0 uF | REMOVE C208. This helps to correct faulty deemphasis in WFM mode. (WFM will sound a lot crisper after this change.) |
| Component Designator | Old Value | New Value | Comment |
| C212 | 6.8 nF | 1 uF | Helps bass response. Watch polarity. (+) lead goes AWAY from Q23 base lead. Q23 is surface-mounted. |
| C213 | 47 nF | 4.7 uF | Helps bass response. Watch polarity. (+) lead goes towards Q23 collector. |
Keyboard Beep Delete
With the top cover removed as described above, locate connector CN3,
a 15-pin connector with colored wires at the front of the main circuit
board. There are two procedures which will stop the beep tone from
being heard through the speaker; read both to decide which procedure
you want to follow.
(1) Find the center grey wire coming from CN3 and cut it midway to
disable the beep tone. You may wish to solder a resistor in series
to reduce the beep volume, a trim-pot to vary the volume of the beep
tone, or a miniature switch to choose between beep and no beep.
SSB Mod
-------------
alt.radio.scanner
Subject: Pro2005/6 SSB MOD HERE!
From: horak@convex.com (David Horak)
Date: Mon, 31 May 1993 18:04:59 GMT
I had a few requests for this mod so I thought everyone would benefit...
This is the mod for adding SSB capability to your Pro2005/2006. It is
taken in part from Bill Cheek's Scanner Mod Handbook Volume 1. As long
as you have a shortwave receiver with an external antenna jack and
capability to tune to 455 KHz, you can interface it to the Pro2006 with
this mod. It is best if you use a static safe work environment to
perform this mod and you should have some technical knowledge. Also, a
schematic would be helpful but is not necessary.
You will need the following parts:
Output jack (I use a 1/8 mini earphone jack but some like a BNC. The
1/8 mono jack is easier to install because you don't have
to drill as big a hole in the back of the unit)
.01 uF capacitor
5 Kohm resistor (1/4 watt)
6 inches of mini coax or other shielded cable
A cable to run from the 2006 to your shortwave. I use the shielded
cable that has the 1/8 plug on one end and a phono plug on the other
end (1992 catalog Radio Shack P/N 42-2444 works for me). The phono
plug is perfect for the antenna input of my DX440 shortwave receiver.
The first step is to remove the cover of the unit and drill a hole in
the back of the 2006 for your 1/8 or BNC plug. (You will want to wrap
some tape around the drill bit about an inch from the end to keep it
from cruising right on into the electronics once it punches through the
metal!) Solder the 5K resister to one end of the .01 uF cap. Solder
the other end of the cap to the shielded coax wire. Solder the other
end of the coax to your 1/8 phono plug (or BNC) and ground the cable at
this end. Now that the cable is in place you are ready to connect it
to the 455 KHz source which is D33. It is on the top circuit board
near the middle left, not too far from a huge capacitor. Solder the
end of the resistor to the cathode of D33. (This should be the top of
the standup part) Now you can test it out before you put the cover
back on to make sure you did everything correct. You should be able
to tune to some local airport or CB frequency on your 2006 and receive
the same thing on your shortwave (with it tuned to 455 KHz and hooked
up to the 2006 of course). If you tune something on your scanner that
is SSB, you should be able to switch your shortwave to SSB and tune in
the signal just fine. Beware of one thing, since the 2005/6 only tunes
in 5 KHz increments minimum, you may notice from time to time that the
signal on your shortwave isn't real clear. It may be that you will
need to tune the shortwave anywhere from 451 to 459 KHz to tune in the
signal well!
If you don't succeed or this description has you baffled you probably
shouldn't be doing the mod in the first place. I assume no
responsibility for screw-ups. Good luck
David
============
Discriminator Mod
http://www.qsl.net/kc8mzm/2006.htm
Local pdf copy
How to tell the new from the old Pro-2006's:
On front panel, old has "DIMMER," new has "LIGHT."
WHAT IS THE DIFFERENCE BETWEEN 200-0145 AND 200-0145A?
The "A" version has the added feature of allowing the backlight on the
display to be turned on and off.
PRO-2006 AS A SATELLITE RECEIVER.
Local copy of the article.
More Realistic PRO-2006 Hardware Modifications
Local pdf Copy of Page
NEW 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:
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.
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.
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