Amateur TeleVision


Original ATV Web Page Information

(October 2002: This page contains the information from my original ATV pages that were published when this site was started several years ago. Since then technology has changed, I have learned more and my plans have changed. I have not completely given up on my homebrew 70 cm AM ATV transmitter project described below. It would be an interesting challenge and could be used in addition to a FM ATV repeater output to generate interest by making it possible for anyone to monitor ATV activity using any cable ready TV.)

ATV Repeater

There has been some local ATV activity on 439.25 MHz in the past, but I would like to generate more interest and some new activity in this exciting mode by establishing an ATV repeater.

I do not have the financial resources to simply buy equipment "off the shelf" (and become simply another appliance operator) so I am investigating the possibility of home brewing a suitable 70 cm ATV repeater transmitter from surplus equipment. Success will depend on finding equipment suitable for modification. Besides, part of the hobby is enjoying the fun and sense of accomplishment from "home brewing" and transforming equipment destined for the garbage into something useful. This is a long term project that I plan to work on, as time permits, along with my many other projects.

But if you are impatient and have several thousand dollars to spare
I am just as willing to spend your money to order, install and
make some ATV repeater equipment operational.

Repeater VE6ATV will hopefully become a reality someday, but for now,
Remember, this is another . . . S l o w l y - B u t - S u r e l y . . . . project!

439.250 MHz AM Output

Goal is for 100 Watts of 439.250 MHz AM Video Carrier
with 10 Watts of 443.750 MHz FM Sound Sub-Carrier

Why use 439.250 MHz for the repeater output?

Because 439.250 MHz AM ATV transmissions are the easiest and least expensive to receive and view. Making it easy to monitor the ATV repeater output is the best way to generate interest and encourage other amateurs to become active in ATV operation. Nothing more than a standard cable ready TV is required to view ATV transmissions on 439.250 MHz since this is the frequency of cable channel 60.

(A cable ready VCR or cable converter could also be used with a non-cable ready TV.)

To receive 439.250 MHz ATV transmissions, simply tune to cable channel 60 using an antenna in place of the normal cable connection. (Make sure that the TV is set for receiving cable channels and not for UHF broadcast channels. (Cable channel 60 and UHF channel 60 are not the same frequency!)

Good AM TV signals are difficult to produce, especially at higher power levels, and a fair amount of power or large, high gain antennas are required to transmit any distance. (A minimum received signal of 180 uV is required for fair TV pictures compared to less than 0.5 uV for FM voice transmissions.) It seems more sensible to build one decent AM ATV repeater transmitter and input FM ATV signals from everyone utilizing inexpensive FM transmitters than for everyone to struggle to produce and transmit an adequate 439.250 MHz AM signal to the repeater and purchase down converters to receive repeater transmissions on higher frequencies. (In-band repeater operation was not considered).

What's been done:

  • A 35 watt UHF Mitrek transmitter has been modified for 30 KHz deviation and is operational on 443.750 MHz as the Aural FM transmitter.

What's next to do:

  • Test 75 watt UHF Mitrek and Micor transmitters to see if either is suitable for use as a linear AM ATV Power Amplifier. If either proves suitable, the next step will be to home-brew a suitable AM video modulator. When one transmitter is operational, the next step will be to increase output power by connecting two RF power amplifiers in parallel. This will allow each 75 watt amplifier to be operated well below its rated output and make it possible to achieve the goal of 100 watts output power and maintaining linearity.

Initial testing of the Mitrek transmitter found it capable of providing over 100 watts of RF output power.

2400 MHz FM Input

Much work has already been done by others utilizing readily available and fairly inexpensive ($100) Wavecom Jr units for amateur TV use. The Wavecom package consists of two units, a transmitter and a receiver. The stock transmitter outputs about 1/2 mw but with a little modification this can be increased to 50 - 100 mw and will provide P5 video up to 1500 feet using 3 inch whip antennas or line-of-site (30 to 50 miles) with gain antennas.

Wavecom units have 4 channels (2398, 2412, 2428 and 2442 MHz). With 2 Wavecom pairs, you could freely roam wireless (perhaps about a field day site) and transmit camera video via channel 1 using a small 3" whip antenna to a receiver at your vehicle up to 1500 feet away. A second transmitter on channel 3 using a high gain antenna could then relay the video many miles to an ATV repeater for reception by anyone within the repeater coverage area.

Update (November 2002)

Wavecom units are almost impossible to find in Canada. I missed Radio Shack's Wavecom clearance sale and their replacement video sender (RS# 15-1971) is completely different from a Wavecom and not worth trying to modify (RF frequency is not even crystal controlled). If I happen to find a Wavecom unit at a garage sale someday, I may get it to modify and experiment with, but today there are better options available that require little or no modification. Check out:

10.5 GHz FM Input ( a possibility )A 10.5 GHz Gunnplexer

Not much news regarding a 10.5 GHz FM ATV repeater input at this time except that Brian, VE6BCA, and Tim, VE6TCJ, and myself have been doing some experimenting with 10.5 GHz gunnplexers but have yet to try any TV transmissions.

A 10.5 GHz Gunnplexer