By Tom O'Hara W6ORG - Email:
Retired owner of P.C. Electronics, The Leader in Amateur Television Equipment for 50 years - history
Last update January 1, 2015
This app note describes a basic crossband ATV repeater with 70cm band input and 23cm band output.
The primary advantage of a crossband ATV repeater is that users can most often see their own video coming back and thereby better adjust their equipment. It also frees up other frequencies in the band for simplex ATV or other repeaters. Repeater cost is less and makes it easier to link to adjacent areas.
Low in and high out at the repeater make the desense filtering easier since there are no transmitter harmonics to track down and remove from the interconnected video, audio and power supply lines. Equipment cost is also less for users, and signal strength greater all else being equal. At first look, one would think that having the repeater output on a cable TV channel would bring in more users. This has not proven true as fewer hams go to the expense and extra effort to transmit a good signal into the repeater on a higher band. Cost of a PC Electronics TVC-12S 23cm downconverter and Directive Systems 2424LYRM Loop Yagi is less than the cost of a 23cm linear amp. With just a small number of the same people transmitting, interest falls off quicker. It is better to encourage activity by having the high power and expense at the one repeater site than at all potential users - note the 70cm and 23cm ATV DX charts.
|Antenna 430-440 MHz||X510NJ||Diamond||P. C. Electronics||$219|
|Antenna 1240-1300 MHz||GP21||Comet||HamCity||$134.95|
|ATV Downconv. 70cm||TVC-4S||P. C. Electronics||P. C. Electronics||$149|
|Ch 3 receiver||Rch3||P. C. Electronics||P. C. Electronics||$89|
|ATV Transmitter 23cm||TX23-.1s||P. C. Electronics||P. C. Electronics||$449|
|ATV Transmitter 23cm||RTX23-.1||P. C. Electronics||eBay, QRZ.com Swapmeet||?|
|30W 23cm Linear Amp||2330PACK||Downeast Microwave||Downeast Microwave||$190|
|Video Operated Relay||VOR-3||P. C. Electronics||P. C. Electronics||$79|
|70cm VSB filter 434.0 MHz||DCI-434.0-6C||DCI||DCI||$399|
|23cm VSB filter 1253.25 MHz||DCI-1253.25-6C||DCI||DCI||$449|
|Die Cast Aluminum Box||1590D-BK||Hammond||Mouser Electronics||$24|
|70cm Low Pass Filter||NLP-550+||Mini-Circuit Lab||Mini-Circuit Lab||$35.95|
|Power Supply 13.8 Vdc @ 2.5A||RS 22-504||Radio Shack||Radio Shack||$39.99|
|Power Supply 13.8 Vdc @ 10A||RS-12A||Astron||AES||$89.99|
|50 Ohm Coax Cable, 250 ft roll||9913 or LMR400||Belden or Times||AES or RF Parts||$129.95|
|Video Identifier board||OSD-ID+w/c||Intuitive Circuits||P. C. Electronics||$129|
Total repeater system cost is about $3000 plus misc. hardware. Prices are of Dec. 2010, so check current prices and sources.
The receiver and control boxes can be mounted in a Bud CB-1372 5.25" high 19" rack panel chassis available from Mouser Electronics as shown for previous models. Another one can be used for the .1 watt transmitter and 30 watt amplifier with fan.
If you think you will some time in the future add a link, crossband alternate input, tower cam, etc., you can substitute the ATVR-4+ ATV Repeater Controller board in place of the VOR-3 Video Operated Relay board and for an additonal $270.
The low pass filter in the receiver antenna line is necessary because cavity or transmission line type bandpass filters repeat at odd harmonics with very little attenuation. If it were not there, the transmitter power picked up by the receiver antenna could pass through the VSB filter and overload the receiver. The VSB filter is necessary to reject other transmitters at the comm site and also prevent intermod generation from other signals mixing in the transmitter final stage.
See the Inband ATV Repeater Example.
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