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VK3KHB
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If you want to transmit (Tx) Television beyond the
boundaries of your property you'll need to hold a amateur radio
operators "certificate of proficiency" a license that ensures you
understand your obligations and have the abilities to undertake the
many technical tasks required.
It is not hard, you may already know much of what you'll need. See the Wireless Institute of Australia website for full details on how to become a amateur radio enthusiast (ham) ~$60 per year (circa 2008).
It is not hard, you may already know much of what you'll need. See the Wireless Institute of Australia website for full details on how to become a amateur radio enthusiast (ham) ~$60 per year (circa 2008).
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Overview: Suitable ATV transmitter. High gain yagi antenna.  The ATV transmitter can be a "you build it kit" or a "cable TV modulator" or a modified "domestic wireless video / surveillance monitoring system" |
Cameras:
Cameras are everywhere now days, so long as you have one with a composite video and audio out you have a source for the ATV transmitter. If you don't have a camera then the output of a PVR, VCR or DVD player can be used, just make sure the content is suitable and be aware of copyright infringements...
Cameras are everywhere now days, so long as you have one with a composite video and audio out you have a source for the ATV transmitter. If you don't have a camera then the output of a PVR, VCR or DVD player can be used, just make sure the content is suitable and be aware of copyright infringements...
Transmitters: (Analog)
On this page we will be referring to the analog "you build it" kits which are designed to operate directly to an anolog TV set or satellite receiver. These kits will be either on 444.25 UHF TV or 1250 - 1283 Mhz satellite TV and need to produce around 2 - 20+ Watts output to the antenna.
For VK3RTV use, only the 1250 - 1283 Mhz kit will work.
426.25 is nolonger available and 444.25 (446.5 Digital) is VK3RTV's output frequency. 444.25 / 446.5 Mhz is permitted but you will be overridden or interfere with by VK3RTV's output.
On this page we will be referring to the analog "you build it" kits which are designed to operate directly to an anolog TV set or satellite receiver. These kits will be either on 444.25 UHF TV or 1250 - 1283 Mhz satellite TV and need to produce around 2 - 20+ Watts output to the antenna.
For VK3RTV use, only the 1250 - 1283 Mhz kit will work.
426.25 is nolonger available and 444.25 (446.5 Digital) is VK3RTV's output frequency. 444.25 / 446.5 Mhz is permitted but you will be overridden or interfere with by VK3RTV's output.
In-House Transmitters: (Analog)
Domestic TV transmitters (AV repeaters) available at all good electronic and electrical stores will do the same job, but they won't work with the ATV repeater or go as far. Current domestic versions operate at very low power (<1-5 mWatts) at 50-200Mhz (VHF) or 530-560Mhz (UHF) or at 2.4-2.5Ghz (UHF) or 5.8Ghz (SHF) and their signal usually contains several harmonic frequencies as well as some frequency drift over time or with temperature. Only good for with-in your property boundry.
Domestic TV transmitters (AV repeaters) available at all good electronic and electrical stores will do the same job, but they won't work with the ATV repeater or go as far. Current domestic versions operate at very low power (<1-5 mWatts) at 50-200Mhz (VHF) or 530-560Mhz (UHF) or at 2.4-2.5Ghz (UHF) or 5.8Ghz (SHF) and their signal usually contains several harmonic frequencies as well as some frequency drift over time or with temperature. Only good for with-in your property boundry.
Antennas:
Antenna for use with the ATV repeater or simplex operation are of a "you build it" type. Domestic TV antenna are only for reception and are not usable to transmit on. Commercially available transmitting antenna are obtainable, they can be expensive and are frequency dependent...
If you have the skills to cut, drill and bend metal tube you can build your own easily. ATV antenna are usually a horizontally polarized Yagi but can be vertical.
Antenna for use with the ATV repeater or simplex operation are of a "you build it" type. Domestic TV antenna are only for reception and are not usable to transmit on. Commercially available transmitting antenna are obtainable, they can be expensive and are frequency dependent...
If you have the skills to cut, drill and bend metal tube you can build your own easily. ATV antenna are usually a horizontally polarized Yagi but can be vertical.
In-House Antennas:
The domestic transmitters (AV repeaters) use vertical polarization via telescopic antennas, these can be modified to fit a connector for use with coax and external horizontal antennas, but their power levels are so low that an expensive amplifier and filter network is needed. So for ATV use outside of your backyard (~30Meters) these become very uneconomical...
The domestic transmitters (AV repeaters) use vertical polarization via telescopic antennas, these can be modified to fit a connector for use with coax and external horizontal antennas, but their power levels are so low that an expensive amplifier and filter network is needed. So for ATV use outside of your backyard (~30Meters) these become very uneconomical...
Transmission Line Coax:
Connecting "transmitter / receiver" to the "antenna" is very important!
The coax feed line must be suitable for use at 1 Ghz frequencies or most of your signal power will be lost in the transmission line as heat.
A low loss ~4-6dB/30m coax like Belden 9913 or RG-8 "foam dielectric" are good at 1 GHZ and relatively cheap. Hard-line coaxes (such as LDF4-50) are much better, but are not cheap. The connectors and connection tool can also be expensive ~$70+ per connector ~$100 for the tool.
At ~1Ghz coax losses for:
RG-8 or 213/214 is around 9 - 10 dB/30m (10watts in for ~2watts out)
Belden 9913 and RG-8 "foam dielectric" 3 - 6dB/30m (10W in ~4W out)
Hard-line coax 2 - 4dB/30m (10W in ~6W out)
For every 3dB of loss... Power presented to the coax arrives at the other end at 50% (half). So 10 Watts at the transmitter injected into 30 meters of 3 dB loss / 30 meters coax arrives at the antenna with around 5 Watts to radiate into space. That means 5 watts is lost in the coax as heat.
It becomes very important to keep losses to a minimum by either using low loss coax feedline and connectors or keeping distance between antenna and transmitter as short as practicable. Mounting the transmitter on the mast of the antenna for Ghz frequencies is possible but fiddly to remotely control DC power, AV signals and monitor RF output power.
Connecting "transmitter / receiver" to the "antenna" is very important!
The coax feed line must be suitable for use at 1 Ghz frequencies or most of your signal power will be lost in the transmission line as heat.
A low loss ~4-6dB/30m coax like Belden 9913 or RG-8 "foam dielectric" are good at 1 GHZ and relatively cheap. Hard-line coaxes (such as LDF4-50) are much better, but are not cheap. The connectors and connection tool can also be expensive ~$70+ per connector ~$100 for the tool.
At ~1Ghz coax losses for:
RG-8 or 213/214 is around 9 - 10 dB/30m (10watts in for ~2watts out)
Belden 9913 and RG-8 "foam dielectric" 3 - 6dB/30m (10W in ~4W out)
Hard-line coax 2 - 4dB/30m (10W in ~6W out)
For every 3dB of loss... Power presented to the coax arrives at the other end at 50% (half). So 10 Watts at the transmitter injected into 30 meters of 3 dB loss / 30 meters coax arrives at the antenna with around 5 Watts to radiate into space. That means 5 watts is lost in the coax as heat.
It becomes very important to keep losses to a minimum by either using low loss coax feedline and connectors or keeping distance between antenna and transmitter as short as practicable. Mounting the transmitter on the mast of the antenna for Ghz frequencies is possible but fiddly to remotely control DC power, AV signals and monitor RF output power.
VK3RTV - Repeater Input Frequency (The
"uplink")
VK3RTV ATV repeater changed from AM to FM analog inputs in the late 1990's and in October 2009 added a DVB-S Standard Definition Digial Video Broadcast. This digital DVB-S (satelite) input is on 1250* with analog FM inputs also on 1250, 1283 MHz & 10.410 Ghz.
(* may change as experiments with adjacent frequencies continue...)
From most areas of Melbourne, amateur stations get a full quieting (no noise) "perfect picture" with a modest 18 element, 2 meter long yagi and using 10 to 30 watts of power for analog operation. While the DiGiTal uplink has studio quality (576 x 720pixel - SD) perfect picture with stereo sound with ~1 to 10 watts.
Most amateur stations have found this to be a vast improvement over the old analog AM / FM TV system where a large yagi (2 - 3+ meter boom) and power levels in the order of 10 to 50+ Watts were needed for similar picture quality. With the installation of a digital up-link another quantum leap is obtained in overall system performance and with the added change over to a digital down-link DVB-T Terrestial, aTV now matches the latest commercial broadcast service standards.
Viewers only need a continious RF (170-870Mhz) coverage "set top box"to receive all TV signals.230-470Mhz is skipped over by most receivers, a manual scan is required and a "aTV" signal must be available for the receiver to store the channel.
The detected channel number will be different for each make of receiver as "aTV" is an "out of band" service, although the detected network ID should be VK3RTV1, VK3RTV2, etc as more AV services are added. Only other amateurs with DVB-T transmitters and using 446.5Mhz will cause a different network ID to be shown...
VK3RTV ATV repeater changed from AM to FM analog inputs in the late 1990's and in October 2009 added a DVB-S Standard Definition Digial Video Broadcast. This digital DVB-S (satelite) input is on 1250* with analog FM inputs also on 1250, 1283 MHz & 10.410 Ghz.
(* may change as experiments with adjacent frequencies continue...)
From most areas of Melbourne, amateur stations get a full quieting (no noise) "perfect picture" with a modest 18 element, 2 meter long yagi and using 10 to 30 watts of power for analog operation. While the DiGiTal uplink has studio quality (576 x 720pixel - SD) perfect picture with stereo sound with ~1 to 10 watts.
Most amateur stations have found this to be a vast improvement over the old analog AM / FM TV system where a large yagi (2 - 3+ meter boom) and power levels in the order of 10 to 50+ Watts were needed for similar picture quality. With the installation of a digital up-link another quantum leap is obtained in overall system performance and with the added change over to a digital down-link DVB-T Terrestial, aTV now matches the latest commercial broadcast service standards.
Viewers only need a continious RF (170-870Mhz) coverage "set top box"to receive all TV signals.230-470Mhz is skipped over by most receivers, a manual scan is required and a "aTV" signal must be available for the receiver to store the channel.
The detected channel number will be different for each make of receiver as "aTV" is an "out of band" service, although the detected network ID should be VK3RTV1, VK3RTV2, etc as more AV services are added. Only other amateurs with DVB-T transmitters and using 446.5Mhz will cause a different network ID to be shown...
"aTV" transmitting antenna
2 meter boom, 70 cm (426 - 444 MHz) or a
1 meter boom, 23cm (1250-1283 Mhz) looped yagi antenna
2 meter boom, 70 cm (426 - 444 MHz) or a
1 meter boom, 23cm (1250-1283 Mhz) looped yagi antenna
From most areas of Melbourne line of site to Mt. Dandenong and ~3 Watt of power "in to an antenna" of ~10dB gain or more will trigger the repeater. The antenna should be horizontally polarized and the use of low loss coax is highly recommended.
Liaison frequency for ATV operations is usually on the 2 meter band at 147.4Mhz FM simplex, but users of the TV service can be anywhere in the amatuer radio bands (HF - SHF) their images usually give call signs and contact details.
73's for now.
Gary, VK3KHB