Pad

Notes on the assumptions: The assumption that the capacitor supplies full power to the final is only going to apply for an almost square envelope output, a case you would only get with either CM or clipping of the sort used b> the Clegg VHF gear. For undipped SSB, a sine wave assumption might be better, in which case only half as much capacitance would be necessary. For full wave rectification only half of that will be required.

The assumption of an allowable 1 db drop in power was taken because 1 db is l he minimum detectable change to the ear. One KW falls off to 800 watts at 1 db down, though, so 1 db might be a bit much.

Don't blame me if somebody's commercial gear uses less capacitance than the equation calls for— they may have settled for a drop of more than that 1 db that 1 assumed. Just say "aaah" into the mike and see if the output power meter drops as (he syllable goes on.

A Simple Oscillator for Monitoring ATV

Ralph Taggart WA2EMC

Monitoring the output of an ATV camera, whether it's a flying spot scanner or a v id icon, can present a few problems. If the TV set you would like to use as a monitor is a fairly new one, there is often a little reluctance about cutting into it to make the necessary modifications, A second problem arises if you want to give a closed circuit demonstration at a ham-fest, club meeting, or at someone else's shack. The usual procedure is to pack both the camera and TV set into the car and take off, but in my case anyway, this produces an inconvenience factor which is directly proportional to the size of the set and inversely proportional to the size of the car. This unit, which will fit into a small Minibox, will solve both these problems. Basically,; it is a low powered TV transmitter which, when parked next to any TV set will allow you to view (.lie output of your camera, with no connecting wires and no set modifications.

Qt serves as an oscillator, tuned to an un-

The ATV monitor oscillator. The aulhor recommends replacing the 2N384 with a more modern transistor such as the 2N1746 if there is trouble maintaining oscillation when the input is loaded.

used TV channel between 2 and 6* The oscillator is base modulated bv the camera, with a 68 ohm resistor serving as a termination for the coaxial cable carrying the camera output, C4 and Lj are the principle frequency determining elements, and with the values shown, it will hit channel 3 or depending on the setting of Lh If output on another channel is desired, one or two additional turns on Lx should get the oscillator on channel 2, while reducing C, to about 10 pf and juggling the number of turns on L1 will give output on channels 5 and 6.

Tie output jack can be a coax connector, a phono jack, or even a binding post- Only about one or two inches of wire connected to the output jack will he sufficient for a good picture when the unit is placed next to the [*V set. Keep in mind that a TV channel is not a ham band, and more output than you need won't improve the picture, but in many cases, it might get von in hot water!

My unit was constructed on a 2\3" piece of Vector board and packaged in a 2)í \ 2-1 \ 4" Minibox. Mounting the input connector at one end, with the output at the other makes a compact arrangement. A SPST switch and a 9 v transistor battery complete the unit. The battery may be taped to the bottom cover of the Minibox, and if you don't forget to turn it off for a week or two running, you should get just about the normal shelf life. The modulation level can be controlled with the camera gain control.

This Utile gadget literally uses only a handful of parts, but you'll wonder what you did without it ... WA2EMC

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