Date: Mon, 13 Dec 93 04:30:55 PST From: Ham-Homebrew Mailing List and Newsgroup Errors-To: Ham-Homebrew-Errors@UCSD.Edu Reply-To: Ham-Homebrew@UCSD.Edu Precedence: Bulk Subject: Ham-Homebrew Digest V93 #131 To: Ham-Homebrew Ham-Homebrew Digest Mon, 13 Dec 93 Volume 93 : Issue 131 Today's Topics: Nation-specific radios (?) and Powering small speakers Send Replies or notes for publication to: Send subscription requests to: Problems you can't solve otherwise to brian@ucsd.edu. Archives of past issues of the Ham-Homebrew Digest are available (by FTP only) from UCSD.Edu in directory "mailarchives/ham-homebrew". We trust that readers are intelligent enough to realize that all text herein consists of personal comments and does not represent the official policies or positions of any party. Your mileage may vary. So there. ---------------------------------------------------------------------- Date: 12 Dec 1993 14:57:05 GMT From: news.larc.nasa.gov!grissom.larc.nasa.gov!kludge@ames.arpa Subject: Nation-specific radios (?) and Powering small speakers To: ham-homebrew@ucsd.edu In article st92ba44@dunx1.ocs.drexel.edu ( antonio gatta) writes: >hello all. > I was just wondering if someone out there might have the answer(s) to >the following: > >1) my grandfather bought a radio last year that was marketed to bring in > a foreign channel (italian news/entertainment) 24 hours a day. He listens > to it all the time so I assume that its working the way it should. Here's > my problem, how does the radio (with only a 2 foot antenna) pick up the > signals from italy 24 hours a day? What kind of radio is it? It picks up a subcarrier from a local FM broadcast station, which probably receives the programming off a satellite feed. Out of curiosity, where is this available? If it's sold in Pittsburgh, I think my parents might be interested in something like it. >2) also, (i have successfully finished my first radio!) and I was wondering > if I couldn't get it to drive a small speaker. Its meant to power a > set of low impedence phones. the book I have has the schematic for > a simple amp but it recommends against using it with the radio I have > built (crystal shortwave). Is there a way to boost the output so as > to drive, say, a 2" speaker? Thanks. Okay, what you need is a high impedance input amplifier, with about 40 dB of gain. This will give you a "line level" signal that you can feed into a small power amplifier. If you can find a design for a microphone preamplifier, that would be a good start. Otherwise, you can use a single op-amp (and I recommend a FET input op-amp like the MC34081) to get you some gain. If you haven't played with op-amps before, I strongly recommend Walt Jung's cookbook volumes, but even the manufacturer's datasheet should have a good enough example. --scott > > > >______________________________________ >antonio gatta >st92ba44@dunx1.ocs.drexel.edu -- "C'est un Nagra. C'est suisse, et tres, tres precis." ------------------------------ End of Ham-Homebrew Digest V93 #131 ****************************** ******************************