S-METER FOR THE PRO-2004/5/6, PRO-43, PRO-2035/2042
      also the PRO-34/37/39 and PRO-2022/2024/2021/2020
   and many other scanners with the 108-136 MHz Aero Band
 ==========================================================
This article/file is for the benefit of all.
(c) 1995-96  Bill Cheek-COMMtronics Engineering
This article/file is for personal use only and may NOT be placed on a
CD-ROM nor any other media that conveys, stores, or transports for
any monetary cost, without expressed permission of the author. This
article/file can only be given away, absolutely free of charge.
                                   -Bill Cheek-
Build the following simple circuit left of Points A and B on a piece
of perfboard for base scanners. Hard-wire it into handheld scanners.
The circuit to the right of A and B is optional, explained further below.
       ||         ||
         (perfboard for base scanners)                 o-------o
Connect                                Jack     Plug   |       |
  to    Y  .01-uF     1N34A                  A   C     v       |
Cathode>----||-----o--->|------o-----o----->(+) >--o-/\/\/\----o
detector           |           |     |                5-k      | 
 diode            ---         ---    \              Trimpot   CB
  in        1N34A  ^          ---    / 68-k                  type
scanner            |    .01-uF |     \           OPTIONAL   S-Meter
                   |           |     |                         | 
Ground >-----------o-----------o-----o----->(-) >--------------0
        Z                                    B   D
       ||||
Diodes must be germanium, 1N34A or 1N60.  Capacitors should be
ceramic disks. Resistor and trimpot are not critical.  The circuit to
the left of Points A and B must be as shown.  If you want to use an
external CB-type S-meter, so much the better....just build the meter
of choice into an attractive or functional project box with a cable
of any length from the box to Points C and D which should be wired to
a male RCA plug for base scanners and a 3/32" mini plug for handhelds..
Connect Point Y to the cathode of:
PRO-2002:  D-119
PRO-2003:  D-122
PRO-2004:  D-31
PRO-2005:  D-33
PRO-2006:  D-33
PRO-2020:  D-120
PRO-2021:  D-24
PRO-2022:  D-29
PRO-2024:  D-24
PRO-2026:  D-30 (Requires verification - not sure)
PRO-2027:  D-24
PRO-2035:  D-34
PRO-2045:  D-34
PRO-32:    D-122
PRO-37:    D-122
PRO-34:    D-117
PRO-36:    D-114
PRO-39:    D-202
PRO-43:    D-302
PRO-44:    D-202
PRO-62:    D-302
Other Scanners:  This mod may work with other scanners that have the
                 civilian aero band of 108-136 MHz.  If your scanner
                 has 108-136 MHz and is not listed above, then find
                 the last 455 kHz IF section, and locate the AM
                 detector diode.  Connect Point Y to the cathode of
                 the AM detector diode.
                 NOTE:  This mod probably will not work with Uniden
                 or Uniden-made scanners.
Keep this Point Y lead length very short, not more than an inch.
Connect Point Z to scanner PCB or chassis ground and keep that lead
short, not more than 1 inch.
Points A and B are the metering points where any DC voltmeter can be
used.  Signal range will be about 0-1v.  The circuit to the right of
A and B is an optional CB type S-Meter, and should be used external
to the scanner. Therefore, it is ideal to wire A and B (length not
critical) to an appropriate jack on the rear panel of base scanners
and on the side panel of handheld scanners, for easy connection of
the external meter.
Otherwise, any DC voltmeter can be used directly at A and B including
a bargraph LED display.  If the external S-meter circuit is desired,
then wire it as shown.  Use a walkie talkie or other transmitter to
send a strong signal into the scanner, and adjust the 5-k trimpot so
that the meter reads exactly full scale.  All other signals will then
read proportionally lower.
Most any analog CB-type S-Meter is ideal for this project, but the
larger the face, the more readable it will be.  There are thousands
of junked CB rigs all over the planet, and most any CB or radio shop
will have a bin full of them.  The cost of a salvaged S-Meter should
be negligible.
You can embelish your S-Meter with a small pilot lamp behind it to
illuminate the face.  Many CB meters have such a lamp built into the
body of the meter.  You may have to tap 12-volt or other power from
the scanner for the lamp, or provide external power.
NOTE:  I cannot and do not supply S-meters.  I can and will provide
technical support of this project on this forum or by e-mail.
Feedback and comments appreciated especially connection points for
scanners not listed above.
(c) 1996 Bill Cheek 
+----------------------------------------------------------------------+
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