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Receiving aTV pictures
The simplest way to receive aTV is by setting up a TV receive system. If you have a "Free to Air" television receiving system, you have all that you need. If you have a Cable TV system then you will need to install an external UHF antenna, which needs to point at "Free To Air" TV station transmitters. These can be centralise transmitters in one place or several places, depending upon the area you are in.
Usually aTV services are from the same place as the "free to air" location but do not have to be, a check with the local amateur radio club may be helpful.This diagram illustrates what is needed and how to configure.
The "Masthead Pre-amplifier" is optional.
aTV is NOT receivable if you watch "free to air" TV services via cable or satellite TV.
The output power from the aTV transmitter is not very strong at around ~30 - 100 watts. The government / commercial / community broadcast stations transmit many Kilowatts. Fortunately at UHF frequencies small yagi antennas have significant amounts of gain so commercial or home brew antenna can be used and both work well with aTV. Note: The aTV transmitter is a repeater. The originating amatuer TV station broadcasts in the direction of the aTV repeater which receives and re-sends that broadcast to the wider area a few seconds later. The delay caused by the receiving system, then re-transmitting.
All TV antenna have a frequency response, depending upon manufacturer.
Generally Analogue services cover at 45-150, 170-250, 520-820Mhz and
DiGiTaL services cover at 170-250 and 520-820Mhz. aTV occupies 440-450Mhz
so is out of the design range but still receivable.
As DiGiTaL is a series of sub-carriers (signals) in a 7Mhz wide channel, these all need to be at a consistent level. If levels are uneven the received picture may not be decoded correctly and a jumpy, blocky picture or a intermittent sound or a "no signal" condition may result. One reason why your old TV antenna may not be suitable anymore.
To ensure you have a good receive signal the best location for an antenna is where there is a clear and unobstructed view of the target area, for the Receiver <> Transmitter. Make sure it meets council by-laws and is secured safely against high winds.
Receivers and Pre-amp's:
To receive aTV signals a TV receiver or Digital Set Top Box capable of tuning 150-800Mhz. Not all TV receivers pick-up frequencies above 300Mhz or below 470Mhz, check the manual or manufacturers website.
If you want to receive the orginating amateur TV station directly you will need either a analog FM TV receiver or digital DVB-S set top box capable of tuning in 1250 MHz (the aTV repeater uplink). Depends upon what type the originating station is using. The aTV repeater always sends out digital and may accept both analog and digital in.
Installation and Alignment:
Obtain an antenna, attach enough coax to run inside to the TV set. Place the antenna on the roof (gutter) making sure its relatively safe from falling and hitting someone (you) and point it towards the transmission site.
Most pre amps and antennas are designed to mount directly to standard TV antenna mast using common U bolts and mast clamps, available from most electrical / electronic / hardware stores.
The coax cable from the antenna to pre amp should be kept as short as possible, a length of 2 meters or less and should be of the larger diameter, low loss variety. The coax cable out of the pre amp to the TV set should be low loss foil shielded RG-59 or preferably quad shielded RG-6, to reduce the chances of strong nearby transmitter signals leaking back into your receive system.
Do the "tuning TV" process to discover what other signals you can receive.
In Metro Areas TV broadcast stations use horizontal or vertical polarization, aTV transmissions generally are to. Horizontal polarization is where the antenna elements (long sticks) are parallel to the ground. The front of the antenna is the shortest width end and points towards the transmitter. The large width end is the reflector which rejects signals coming from the back of the antenna.
A masthead pre-amplifier needs DC power.
One connector on the power supply (or power inserter) feeds DC volts to the pre-amp via the coax. Make sure you do NOT connect this DC side to the television, damage to both may occur. The other connector has a DC blocked output (a capacitor) for the TV set.
There are a few reasons why you may not be able to receive aTV.
1. aTV broadcasts are beyond your TV receiver frequency range.
2. There is no one sending a signal.
3. The signal in your area is too weak to receive. (Pre-amp?)
To resolve which of the above is the cause, try again later or contact one of the aTV operators to put up a signal.
Check your TV's handbook on how to receive signals between 300 MHz to 450 MHz.
aTV is at 444.25Mhz analog or 446.5Mhz digital, most digital receivers do not tune in aTV signals directly. Manual tuning is required. As aTV has no assigned channel number, you may have to input the frequency and select "scan for service". Sadly you may have a receiver that can not receive in this frequency band.
VK 3 RTV outputs at 446.5Mhz this is called the "Downlink" as the signal comes down from the hill... To receive aTV at 1250 MHz FM, called the "uplink" you'll need special equipment. A satellite television receiver, a purpose built antenna, a 1250 MHz pre amp (optional), low loss coax and a line of sight with the sending station; In brief, this is more of a challenge but still simple to do.