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Amateur TV Repeaters and System Information By Bil K1ATV

The most common Operational modes:

(L)—linked (E)—Emergency power (PL)—PL Tone (RM)—Remote (S)-Simplex (SS)-Slow Scan TV (ATV)-Fast Scan TV (*) Nominal TV Horizontal Sync Pulse

Output Input Location Call Tone Access Operation COMMENTS / COVERAGE
1253.25 MHz VSB 2441.5 MHz FM TV, 434.00 MHz AM, VSB White Tanks ATN-AZ W7ATN 15.75 KHz* ATV, Now linked to Mt Lemmon (2417.5 MHz FM TV out, audio is on the 6.0 MHz subcarrier). Central Phoenix, Mesa and far West Valley, including Tonopah
1277.25 MHz VSB 2441.5 MHz FM TV (future plans), 434.00 MHz AM, VSB Mt Lemmon ATN-AZ W7ATN 15.75 KHz* ATV, Now linked to White Tanks (1277.25 MHz VSB out). Will be linked to Green’s Peak, also. Most of Southern AZ, including East Valley
1289.25 MHz VSB 2441.5 MHz FM TV (future plans), 434.00 MHz AM, VSB Green’s Peak ATN-AZ W7ATN 15.75 KHz* ATV, Will be linked to Mt Lemmon (2417.5 MHz FM TV out, audio is on the 6.0 MHz subcarrier). Eastern Arizona and Western New Mexico
421.25 MHz VSB, 1241.25 MHz VSB 434.00 MHz AM, VSB, 1265.00 MHz FM TV Shaw Butte AATV W7ATV 15.75 KHz* ATV - Can be operated separately but usually aren’t. Most of Central and NW Valley

ATV System Information For Arizona

Arizona currently has 4–5 ATV repeaters in operation.

Great News As Of 2013

The White Tanks HAM TV repeater has a new call sign. The new call sign is W7ATN. It is now linked full time to the Mt Lemmon repeater. 2417.5 MHz FM TV out. The Mt Lemmon repeater is now linked full time to the White Tanks repeater. 1277.25 MHz VSB out. The Green’s Peak repeater is now on the air.


ATV for Beginners By Bil K1ATV

ATV 101

This article will not deal with the video part of the TV signal but only with the RF part. It will not deal with HDTV or stereo sound either. It will deal with the RF parts of the old-fashioned TV signal only.

There are two basic types of RF - AM and FM. There are others but they will not be dealt with here. FM will be dealt with very briefly in passing.

Difference between AM and FM

AM consists of a constant frequency carrier modulated by mixing audio (as in the standard AM radio band) or video (as in television) or, in a few cases, both. The amplitude of the result varies with the input signal.

This mixing results in three outputs: the carrier itself and two sidebands - upper and lower - which carry identical mirror images of the modulating signal.

For example, assume an AM station on 1000 KHz. When an audio frequency - say 1000 Hz - is mixed with the carrier we get the original 1000 KHz and 1000 KHz minus 1000 Hz (999 KHz) and 1000 KHz plus 1000 Hz (1001 KHz). In the case of AM radio the frequencies can be up to about 5000 Hz or more.

In the case of television the modulating signal will be a band of frequencies up to about 4 MHz wide. Therefore, the video signal created could be up to 8 MHz wide - carrier minus 4 MHz and carrier plus 4 MHz. Color and audio can increase this up to 9 MHz wide. More on this later.

FM varies the carrier frequency itself and the amplitude remains the same. The modulating signal can be as high as 100 KHz since an FM radio channel is at max, 200 KHz wide - as opposed to 10 KHz for AM radio.

Types of Amplitude Modulation

There are several types of AM - Double Sideband with Carrier (commonly known as AM radio), Double Sideband with reduced or suppressed carrier (which is rarely used), Single Sideband with carrier (rarely used), Single Sideband with reduced - or usually suppressed - carrier (known as SSB), Vestigial Sideband with carrier (VSB - as is used in American TV), and Independent Sideband with carrier.

I dare say that we are all familiar with SSB since almost all ham HF operation is of this type. The carrier and one sideband are suppressed.

Independent Sideband has different information on each sideband - unlike “regular” AM which has, as described above, the same information in mirror image on each sideband.

Television uses VSB. A full 9 MHz wide signal is created but all of the lower side band (LSB) except for 1.25 MHz below the video carrier is truncated. Thus, all that is left is a vestige - hence the term “vestigial” - of the LSB. Some LSB must be left so that the TV receiver can lock on to the carrier. As been said above - the LSB information is a mirror image of the USB information so no information is lost.

Except for the two ATV channels at the band edges - 421.25 MHz and 1241.25 MHz where VSB is mandatory - VSB is not required for HAM TV. VSB filters are expensive.

Audio in TV and HAM TV

Standard American TV has separate video and audio transmitters 4.5 MHz apart with the audio transmitter “above” the video transmitter. HAM TV uses one of two methods for audio transmission: subcarrier audio or on-carrier audio.

On-carrier audio is probably the older of the two methods stemming from the use - early on - of converted UHF commercial two-way radios. The radios were modified to run wideband video and the video was AM’ed on to the carrier. The audio was left basically unchanged.

As equipment was designed and built specifically for HAM TV a separate 4.5 MHz FM subcarrier was used. The audio is carried on the FM subcarrier and then the resultant FM signal is AM’ed on to the video carrier. The TV receiver cannot tell the difference. Because DSB is used and we don’t usually use the VSB filters the ATV signal is a little over 9 MHz wide. As in American TV the color information is generated in the video source itself so no external circuitry is required.

Up until about ten years ago some new ATV transmitters were still available with on-carrier sound but it is not used much out west.

If there are any questions, additions or corrections feel free to contact me directly.

Bil Munsil K1ATV HAM TV Mesa AZ

For More Information About ATV Checkout The Links Below

Amateur Television Network

Arizona Amateurs on TV

Az HAM TV Yahoo Group

P. C. Electronics

National HAM TV Yahoo Group

W7ATN (White Tanks) coverage map

W7ATN (Mt Lemmon) Coverage map

For additional system information or to submit data or comments please Contact Bil K1ATV the editor of this page K1ATV

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Page last modified on December 24, 2015, at 06:58 AM EST by N8DJR