Newsgroups: alt.radio.scanner
From: parnass
Subject: Improved audio for the PRO-43 portable scanner
Organization: AT&T Bell Laboratories, Naperville, IL
Date: Wed, 2 Dec 1992 01:15:35 GMT
Message-ID: <1992Dec2.011535.16065
Keywords:scanner radio, audio, modification, midband sensitivity
Lines:45
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IMPROVED AUDIO FOR THE PRO-43 SCANNER
by Bob Parnass, AJ9S
The Radio Shack PRO-43 scanner audio is too bassy.1 The
lack of treble makes it difficult to hear the PRO-43 in
noisy situations, especially whilelistening in a car
or truck. LouisShirleysent mea schematic andsug-
gested I remove C341, a tiny 0.015 ufd surface mount
capacitor.
I'm glad to reportthat removingC341 made a great
improvement. The audiois nowmuch "crisper,"more
like the Uniden 200xlt, although still not quite as
loud. Turning the volume control up still overloads
the PRO-43's small, internal speaker, but there'sless
need to dothat once C341 is removed.
The PRO-43contains 3 printed circuit boards, and the
middle (second) board containsthe audio circuitry.
Finding C341 is difficult,as it is neither markedwith
avalue nor a component designation. It is located on
the foil side of the middle board, under IC304, an
LM386 amplifier IC. C341 is in parallel with, andphy-
sically next to, R350 (33,000 ohm). R350is slightly
larger than C341 and is marked 333. Both R350 andC341
are connected between pin 2 of theLM386 and ground.
A Note About 50-88 MHz Reception
Now that Ihave a schematic, I see that the European
version of the PRO-43 has different coils and capaci-
tors in the low (mid) band front end filter.That
explains why the 75 MHz sensitivity isn't stellar after
adding diode D3 toenable 30-88 MHz coverage.
__________
1. See"PRO-43ProductReview," by BobParnass, AJ9S, in
theNovember 1992 RCMA Journal.
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Bob Parnass, AJ9S - AT&T Bell Labs - parnass
SOURCE: The QRZ Windows Ham Radio CDROM |
