mahaun@sactoh0.UUCP (Mark A. Haun) (01/09/90)
About a year ago, I came across an article in an old issue of 73 Magazine titled "800-900 MHz The Easy Way" -- it was in the October 1987 issue on page 40. Basically it described a way to convert an old UHF TV tuner into an 800 Mhz scanner converter by hooking up an antenna and power supply to the tuner module, and then using the scanner to listen to the (about) 45 MHz IF output. The article was quite short and didn't describe much about the details of using specific types of tuners, although it did contain a low-drift power supply design (the tuner frequency is very dependent on supply voltage). Around the same time, I found the following advertised in a surplus electronic & radio parts catalog (Fair Radio Sales, Lima, OH): "UHF Tuner: UHF varacter tuner, covers 450-900 MHz; use for TV repair or modify for scanners, etc. Approx 47 MHz IF output; 300 ohm ANT input, 50 ohm OSC out. Requires +15 (B+), 3-10 (AGC) and 0-30 VDC (tune). 3.5x3.5x1, 1lb. GE #EP85X66" Thinking this would make a fun and useful project to hear 800 MHz on my BC-100XL scanner, I went ahead and ordered the unit. When it arrived, I noted that a sticker on it read "EP86X65," contrary to the GE number quoted in the ad. It also came with a small sheet listing tune voltage vs. frequency. The unit itself is a small metal box with a clearly labeled "IF out" jack with an RCA-type connecter, and three terminals labeled "AGC," "B+," and "T". Unfortunately, when I tried hooking it all up, I was unable to receive anything different in the 45-47 MHz range of my scanner. I think the problem may be in the currents I am supplying to the three control terminals. Does anyone who is familiar with these units know the typical current requirements for the varactor diode tune input and the AGC input? Also, I have no idea what the voltage on the AGC input should be set at to start with. There are two holes in the top cover marked L13 and L11 with ferrite slugs inside that can be adjusted -- is it possible that I need to mess with these? Surely someone reading this has used one of these goodies before... if so, please send me an email address so that I can discuss the details with you. If I figure this out and get it working, I will post a summary of the super-deluxe $20 scanner converter :-) Thanks in advance for any help anyone can provide on this! -- ( Mark A. Haun KJ6PC )( UUCP: ...ames!pacbell!sactoh0!mahaun ) ( Sac-Unix, Sacramento CA )( AMPRNET: kj6pc@kj6pc.ampr.org ) ( IP: [44.2.0.56] 144.93 Mhz )( PACKET: kj6pc@wa6nwe.#nocal.ca.usa.na ) ( INTERNET: mmsac!sactoh0!mahaun@sacto.West.Sun.COM )