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VK3KHB
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The simplest way to receive ATV is by setting up a receive system. If you have a "Free to Air" television receiving system, you already 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.
In Melbourne Mt. Dandenong is the main TV transmission site for all free to air services including aTV.
If Your TV antenna points toward the City or you watch "free to air" TV services via cable TV.
Antennas:
The output power from the ATV repeater is not very strong ~30 watts
compared to a broadcast station of many Kilowatts. Fortunately at UHF
frequencies small antennas have a significant amount of gain. The yagi
antenna is the most common in use for ATV. Different types of antennas
can be used, either commercial or home brew, both types are in use.
All TV antenna have a frequency
response:
for Analogue services it starts at 50-150, 150-300, 470-800Mhz.
for DiGiTaL services it starts at 150-300 and 470-800Mhz
ATV occupies 440-450Mhz just out of 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 consistant 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 the old TV antenna may not be suitable
 A commercially available 18 element UHF TV antenna with preamp (box at bottom) |
 Home brew, (you build It) 20 element 70 cm (426Mhz) yagi.  Home brew, (you build It) 20 element 23 cm (1250 MHz) yagi. |
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 (Your site <> Mt.Dandenong). Make sure it meets council by-laws and is secured safely against high winds.
TV stations also retransmit their signals in the UHF band Ch 21 - 69 from different locations around the city and at lower power levels. These re-transmissions are to reach areas blocked by high rise buildings or in low lying areas. ATV is NOT retransmitted from these locations.
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Receivers and Preamp's: To receive ATV signals all that is needed is a standard UHF TV receiver or Digital Set Top Box capable of 150-800Mhz reception. (Not all TV receivers pickup frequencies above 300Mhz or below 470Mhz, check your manual or manufacturers website for specifications.)
To receive the analog FM TV
or digital DVB-S 1250 MHz uplink, a satellite receiver is
needed.    |
with
built in
UHF tuner.Installation and Alignment:
Obtain a UHF 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 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 RG-6 for its
better shielding, to reduce the chances of strong nearby transmitter
signals
leaking back into your receive system.
Now do the "tuning TV" process to discover what other signals you can receive.
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Antenna & pre amp. |
In Melbourne broadcast stations use horizontal 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 The large width end is the reflector and this rejects signals coming from the back of the antenna. |
A masthead pre-amplifier needs DC power. One connector on the power supply (or power insertor) 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. Your TV receiver is out of
band / frequency range for ATV broadcasts.
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. If your TV is "cable ready" it should be able to receive ATV broadcasts, check your TV's handbook on how to receive signals between 300 MHz to 450 MHz. (ATV is at 444.25 or 446.5 Mhz.)
The VK3RTV ATV repeater output at
44x.x Mhz is called the "Downlink" as the signal comes down from the
hill... To receive ATV at 1250 MHz FM also called the "uplink" to
VK3RTV, 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 signal; in brief, this is more of
a challenge but still simple.
