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Receiving ATV pictures
Tuning in aTV



Starting out:
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.

In Melbourne Mt. Dandenong is the main TV transmission site for all free to air services including aTV. The below diagram best illustrates what is needed and how to configure.

The "Masthead Pre-amplifier" is optional.
aTV is NOT receivable if:
Your TV antenna points toward the City or
You watch "free to air" TV services via cable or satellite TV.

Antennas:
The output power from the aTV repeater is not very strong around ~30 - 100 watts compared to the government / commercial / community broadcast stations of many Kilowatts. Fortunately at UHF frequencies small yagi antennas have significant amounts of gain and is the most common in use for TV. Commercial or home brew antenna can be used and both work well with aTV.

All TV antenna have a frequency response, depending upon manufacturer:
Generally Analogue services cover at 45-150, 170-250, 520-820Mhz
Generally 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 "no signal" condition may result. One reason why your old TV antenna may not be suitable.

Receive only antenna.

A commercially available
18 element UHF TV antenna
with preamp (box at bottom)
Transmit and Receive antennas.

Home brew, (you build It)
20 element 70 cm (444 Mhz) yagi.


Home brew, (you build It)
20 element 23 cm (1250 MHz) yagi.

Antenna Location:
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 27 - 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.

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.)

Pre Amp and Power Supply.

DC Insertor Plug Pack Supply
Analogue / DiGiTaL TV

To receive analog FM TV or digital DVB-S on 1250 MHz (uplink),
a satellite receiver is needed.

Typical satellite receivers.




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 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.

Now do the "tuning TV" process to discover what other signals you can receive.

Antenna mounted on a rotator with a mast head pre-amplifier.

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 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. 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. 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.

The diagram illustrates a typical 23 cm (1250MHz) ATV receiving system.
Typical 23cm Receive System - Diagram from Melb. ATV Group
The masthead pre amp is optional,
it is usually required but can be left off.
The originating aTV transmitter could be anywhere in Melbourne metro area.


73
Gary, VK3KHB

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