ATV Add-ons.

This page started on 10/05/03
Latest changes 25/07/08
(Please also see the 'project' pages for more equipment.)


Caption generator 4-I/P switch AV mixer PIC Dream
"Low cost caption generator"
by Steve Drury G6ALU
"4-Input Vision Selector"
from the ATV Compendium
"Video fader & audio mixer"
CQ-TV 140
"PIC Caption Generator"
by Alain Fort

Cropredy Video distribution amp 6270 VOGAD
"Test Card Generator"
The Cropredy
"Video Distribution Amp"
using discrete circuits

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"A Low Cost Caption Generator."

by Steve Drury, G6ALU
Described in CQ-TV 201 page 23.

Opened up The pcb
My diecast box opened up.
Note the 'double' EEPROM & switch. (see close-up)
This is the high quality pcb provided by Steve and the Milton Keynes club.

Caption pages are stored on an EEPROM, which is fully (and easily) programmable using a PC keyboard. This website has all the information including PCB design files, MC50555 data sheet, PIC assembler files and a copy of the CQ-TV article. Details are given of the excellent PCB and a programmed PIC available from Steve. I went on to add a second EEPROM selected by a slide switch on the baseplate. This gives me an alternative range of captions suitable for /M and /P operation.

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"4-Input Vision Selector"

from the ATV Compendium p8-9.

Vision selector

The required channel is selected by a rocker push switch and marked by an LED (tally light) in the switch. Gain of each channel can be pre-set accessible by a screwdriver in one of the 4 holes in the lid. I added a video distribution amp so that the video to the TX can be monitored on a separate output.

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"Video fader & audio mixer"

CQ-TV 140 p7-10.

A/V mixer/fader

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"PIC Caption Generator"

by Alain Fort, CQ-TV 180 1997, p79-80.

PIC Dream

I made mine on a pcb designed by Howard, G3NZL, for the SCART club. The PIC, a 16C84, was kindly programmed for me by Dave, G0GMK. I wanted to use mine away from the shack (and the +12 volt PSU) so I have put a 9v battery (PP3) inside the box. A switch enables me to either select the internal battery or an external nominal 12v, in which case the LED lights to show it is powered. I have found that its small size and internal battery makes it an extremely useful video source for testing all kinds of video equipment like monitors and ATV TXs. I don't find the internal clock much use as it has to be set each time power is applied; I will probably try to use that part of the screen (and program) for something else. I also intend to add a colour coder but this may make it too big for the existing diecast box as well as run the battery down even faster! Rather than modify this unit I will make a second one in which to try out these ideas.

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"Cropredy Test Card Generator."

Originally by Colin Edwards in Radio & Electronics World, July 1983.

Also: CQ-TV 139 p20-23, CQ-TV 141 p55, CQ-TV 155 p21-23, CQ-TV 156 p26-27, CQ-TV 162 p43 & CQ-TV 163 p24.
EPROM programs: Cropredy.exe by G1FEF and Cropedit by GW6BWX, with modifications in CQ-TV 172 p87 by G8SUY.

The box

This is how I have boxed my Cropredy.

From Left to Right are:
  • The EPROM select switch (not yet used)
  • Test tone (not yet used)
  • Power ON/OFF and red LED
  • 75 Ohm Video out.

inside the Cropredy

Here you can easily see the EPROM with blue label. It is held in a 28-pin ZIF socket. The intention is to add a pcb with several EPROMs that can be selected by the rotary switch on the front panel.

The small experimenter's board at the lower Right is the colouriser circuit (CQ-TV 139 p20-23). The BNC socket on the back panel (upper Right) will be used for audio out from a test oscillator or even a callsign generator. At the moment it is used for a 'scope trigger pulse.

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"Video Distribution Amp using discrete circuits."

CQ-TV 148 p44.

Video distribution

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"VOGAD" using SL6270
(obsolete many years ago!)

VOGAD unit
Vogad unit with electret mic.

I have seen VOGAD circuits using op amps with an FET to control gain, published long ago in Ham Radio Today and Wireless World. Steve G6ALU has a similar design which he describes on his website (see "Radio related items" then "AGC amplifier").

An "Audio Level Control Unit (VOGAD)" project was presented many years ago by L. Nelson-Jones, G4JDW to The Bournemouth Radio Society. I built one from his kit and found it worked well. Unfortunately, the kit is not available to buy and he requested that I do not pass on the design details (note the copywrite symbole on the PCB), However, it is similar to G6ALU's circuit referred to above.

completed board VOGAD boxed
The G4JDW 'kit' completed and working. Mounted in a diecast box that I modified
and it still works well!

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