Newsgroups:alt.radio.scanner From:parnass@cbnewse.cb.att.com (Bob Parnass, AJ9S) 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@cbnewse.cb.att.com> Keywords:scanner radio, audio, modification, midband sensitivity Lines:45 x 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. -- ============================================================================== Bob Parnass, AJ9S - AT&T Bell Labs - parnass@ihlpm.att.com - (708)979-5414  Amsterdam View Our Stats   CLICK FOR A FREE DOMAIN NAMES HTTP://WWW.YOURNAME.TK FOR YOUR OWN WEBSITE IF YOU CLICK HERE AND YOU CAN VOTE FOR OUR FREE WEBSITES IN THE TOP 100 LIST  WANT A TOP RANKING ? USE THE ULTIMATE SOFTWARE SUITE FOR WEB SITE PROMOTION  FreeWebSubmissions Submit Your Site To The Web's Top 50 Search Engines For Free THE ALEXA BANNER, THIS BANNER GIVES THE DALLY STATISTICS OF THIS FREE WEB SITE The World of Free Packet Radio Software Amsterdam The World Of Free Packet Radio Software Amsterdam The Netherlands |