"TV tuners".

At the January 2000 SBMS meeting Kerry, N6IZW, brought in some surplus "TV tuners", Toshiba model CVA-151 (RCA connectors) and CVA-113 (F connectors). These have a number of surface mount parts inside and everyone was encouraged to take several home. The now defunct "Ham Radio Magazine" had a series of articles on various spectrum analyzers, electronically tuned receivers and things that could be done with excess TV tuners. Ham Radio September 1986 page 82, March 1987 page 99, September 1987 page 49, September 1988 page 84, and Communications Quarterly premier issue fall 1990 all had something to do with the basic TV tuner. The older tuners had a VHF and a UHF section that allowed receiving signals from 50 to 300 MHz and 500 to 800 MHz. IF outputs were in the 45 MHz range. This set of articles added the 3089 FM receiver on a chip plus an audio amp to make a panadaptor, spectrum analyzer, or tunable receiver from the basic circuits in the first article to the addition of computer control and spectrum analysis in the last modifications article. More recently "73 Amateur Radio Today" magazine had a 3 part series by Hugh Wells, W6WTU, on "TV/ VCR Tuner Applications" in the April 1997 page 18, May 1997 page 36, and June 1997 page 30 issues. Wells indicates the newer "cable ready" tuners cover 45 MHz to 900 MHz with an IF of 47 MHz for the TV units and 63 MHz for the VCR units. Again with the marriage of either some chips or another IF receiver and sweep circuits or a pot, one could build some interesting receivers from junk box parts. The tuners from the SBMS meeting appear to only cover 30 to 400 MHz. But there are some interesting circuits inside. They seem to have an input filter, a VCO, a prescaler, and mixer in the first module. A 600 MHz filter, narrow tunable VCO, mixer and some filtered output amplifiers in the second module. See Chuck's drawings.

The first module VCO tunes 500 to 1100 MHz. The prescaler divides the VCO by 64 in the CVA-151 and by 256 in the CVA-113 and provides a TTL output. The mixer provides a 600 MHz output to the second module from the combination of the input signal and the VCO. Applying +12v to pins B1 and B3 power up the devices. B2 for the prescaler wants to be +5v. . The prescaler TTL output is on pin PS. The first VCO tuning voltage is applied to pin VT and can range from zero volts (500 MHz VCO frequency) to about 25v for 1100 MHz. The VCO is quite stable for the amount of circuitry inside.

The second module has a VCO that operates 560 to 570 MHz with application of zero to 25v on pin AFC. The output circuit bandwidth is close to 20 MHz to accommodate the full TV signal spectrum. These tuners appear to be built for cable or similar operations where high-level signals are present so if one wants to use it for a receiver, some preamplification needs to be added in front of the tuner.

Another use of the tuner might be as a signal generator. If one were to strip out the front-end filters and replace them with an MMIC, one could couple the strong VCO signals to the "input" connector via a buffer amplifier. Using the prescaler and a HF counter one could display the signal generators frequency (divided by which scale factor tuner you have). Another signal generator version could take the AFC VCO signal into the first module mixer. This way the mixer output would be near DC to 500 MHz. Thus you could have a voltage tunable signal generator covering from DC to 1100 MHz with two tuner units. Have fun. Bill, WA6QYR

73's Bill