Triangle ATV Association
The Triangle Amateur Television Association is a non-profit corporation that was formed on January 14, 1993 by a group of approximately 22 hams from Raleigh, Durham, and Chapel Hill, NC. The initial goal of the Association was to form an independent organization of Triangle area Hams to promote ATV in the Triangle area and to build and operate a state-of-the-art, wide-area coverage ATV repeater.
ATV Repeater
The Triangle ATV Association's ATV repeater was placed into service in March of 1996. The repeater is located atop "TV Hill" in western Durham county at approximately 790' ASL with a 360 degree view of the horizon which provides good coverage in the Raleigh, Durham, Cary, and Chapel Hill area.
Repeater Features:
Repeater call sign - KJ4SO
Repeater input frequency - 434.00 MHz (cable ch. 59)
Repeater output frequency - 421.25 MHz (cable ch. 57)
Horizontally polarized, omni-directional, 8 dB gain antenna (Two Alford Slot antennas)
Antenna height approximately 790' ASL fed with 7/8 Heliax
TX-RX Duplexer
2 - International Crystal Mfg. VSB filters (RX & TX)
Jerrold C6MII CATV modulator
M57745 20 Watt driver amplifier
Teletec ATV repeater 150 Watt power amplifier
PC Electronics ATVR receiver
ELKtronics Video ID unit
Microprocessor controlled ATV repeater controller/video switcher
(10 video, 4 audio inputs)
Here are some photos of the repeater site:
The building housing the repeater
A view of the tower suporting the ATV antennas, above the treetops
Closeup of the Alford Slot antennas, with commercial UHF folded dipole arrays visible nearby
A different angle on the ATV antennas, slightly closer
Detail view of one of the slot antennas
Planned Enhancements:
Weather Radar (NOAA Doppler Radar)
1.2GHz ATV Receiver
TVRO satellite receiver with 10' dish (on-site) for NASA Select
Tower Cam (Remote controlled tower mounted color camera with pan,
tilt, & zoom)
Links to other ATV Repeaters
In addition to the enhancements for the Durham ATV repeater, we are building a second ATV repeater which will be located in Raleigh, NC. The Raleigh repeater will be a split-band repeater with RX inputs on 1.2 GHz and 2.4 GHZ FM, and TX output on 421.25, VSB and 2.4 GHz FM. Both the Durham and Raleigh repeaters will be linked full time on 2.4 GHz.
Both repeaters will transmit on 421.25 MHz. However, the Raleigh repeater antenna will be vertically polarized, and the Durham repeater will remain horizontally polarized. The cross-polarization is expected to provide the necessary isolation between the two transmitters.
Association Goals
Public Service operations
SkyWarn - NOAA Weather Radar
ARES - On-site damage assessment for the State and County E.O.C.
Educational purposes - TVRO satellite receiver on-site to provide
"NASA Select" for Space Shuttle rebroadcast
Association Meetings
The Triangle ATV Association meets
on the 4th Thursday of each month for dinner at 18:30, and business at 19:30.
The current meeting place is Fazoli's restaurant on NC highway 55, just south
of its intersection with NC 54 in Research Triangle Park. It's on the left and
has bright neon signs, so you can't miss it! From I-40, take the "Apex" exit
and head South.
Meeting announcements are sent out via our Association's e-mail list server.
Contact Information
The Association maintains an Internet e-mail mailing list that is
used to send local area hams meeting announcements and miscellaneous ATV information. If you would like to be
added to this list, send your request to Nick KD4CPL at nick@cs.unc.edu. 
For specific questions about the Association, send e-mail to tri-atv@qsl.net.
ATV BASICS
AMATEUR TELEVISION OVERVIEW
The Triangle ATV repeater is an "In Band" 70cm
repeater with its input on 434.00 and its output on 421.25. The
video and audio comply with NTSC standards, which means that you
can use a standard TV set for receiving ATV signals by simply
retuning it to the proper 70cm (440 MHz) frequencies, or by
placing an ATV "Down Converter" or some other type of
receiving converter between the TV set and the antenna.
An ATV station does not have to be expensive. Many hams
already own most of the basic components required for an ATV
system: a TV set, a VCR, and probably a video camera (camcorder).
The least expensive approach to receiving ATV transmissions in
the 70cm Amateur band is to use either a "Cable-Ready"
TV set, or a standard VCR tuned to cable channels 57 - 60
as a "down converter" in front of a standard TV set. There are four
ATV channels in the 70cm band: 421.25, 427.25, 434.00, and
439.25. These frequencies correspond to Cable TV channels 57, 58,
59, and 60 respectively. Please note that Cable TV channel
frequencies are different than UHF TV frequencies. The 70cm
Amateur Radio band is just below UHF TV channel 14. All you have
to do is connect an outside antenna to the cable input of the TV
or VCR and adjust the TV or VCR to receive "Cable"
frequencies instead of "Broadcast" frequencies.
VCRs and most TVs are designed to receive the high level TV signals from broadcast stations running RF power levels measured in hundreds of thousands of watts or even megawatts of effective radiated power. The Triangle ATV repeater operates with 245 watts ERP - so the antenna used for receiving ATV signals and the sensitivity of the ATV receiver are very important. You will get the best results with a horizontally polarized, high gain Yagi (Beam) antenna pointed toward the ATV repeater. If you live close enough to the repeater you may even get by with using a vertically polarized 440 MHz FM antenna.
Many hams have re-tuned standard
UHF TV tuners to receive 70cm ATV signals. Many of the
small portable TVs that have slide-rule type tuners are very easy
to retune since they are tuned by a potentiometer that varies the
D.C. voltage to a varicap diode. You simply adjust the calibrate
pot to "slide" the tuning range down just below UHF
channel 14.
ANTENNA SYSTEM
The antenna system is the most important part of your ATV system. Trees, foliage, houses, etc. greatly absorb UHF energy. When compared to FM voice systems with the same power, antenna, etc., an ATV receiver's sensitivity is reduced by 26 dB because the receive system bandwidth is increased from 15 KHz to 3 MHz. With this bandwidth the noise floor is around .8 pV. So, you can see that quality coax and high gain antennas mounted as high as possible are necessary to make up this difference compared to the DX you are used to with FM simplex. When it comes to ATV, as well as most other Amateur Radio VHF/UHF communications, there is no such thing as "too much" antenna gain.
Antennas for ATV work must also have broad bandwidth as well as gain. Most high gain Yagi types have only 1% bandwidth, or 4 MHz at 70 cm. In ATV applications, this will give less gain and higher VSWR to the most important color and sound subcarriers - assuming that the antenna was cut for the exact video carrier frequency in the first place. The best true reference for antenna gains and performance is the results of the various VHF/UHF Conferences' antenna measuring contests held annually and publicized in the ham magazines. Advertising claims have become mostly wishful thinking and sales hype.
M2,
K1FO, and KLM manufacture excellent ATV antennas. Home-brewed
antennas using K2RIW and K1FO type driven elements are
also good choices for ATV.
ANTENNA CABLE
Flexi-4-XL or 9913 style coax is recommended. For runs over 100' you may want to consider investing in some good copper hard line or an antenna-mounted low noise preamp. An antenna-mounted preamp can increase receive sensitivity by an amount equal to the coax loss. Use type N connectors for all coax connections. PL-259 coax connectors are not suitable for 70cm and above.
LINKS TO OTHER INTERESTING ATV RESOURCES
Last Modified 20000622 by K4SAR
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