Guide to Transmitter Components


What equipment would we need?

 1   Program Source / Feed

In order to transmit a TV program you will need a source or feed, which could include any of the following:

a)       Downlink equipment  (Use as large a dish as possible, to avoid breaks in transmission caused by bad weather)

b)       DVD player

c)       Live camera link (from studio or church)

d)       Program server to play out programs at required times

 

2    Mixer or switching device

To route the input source to the transmitter.
This could range from a simple (hard) switch to more sophisticated mixers
 

3    Studio to Tower transmission Link (STL ) 

Where your studio is some distance from the transmitter tower, but within line-of-sight, the following links could be used:

  • Microwave link (usually up to 8 – 10 Km)
  • Low loss cable (distances below 400m)


4    Transmitter

Such a transmitter may transmit on the UHF or VHF bands and be either analog or digital.  Many countries are migrating to digital transmissions in order to free up the spectrum in cities, enabling more channels to broadcast.  As many as 6 or 8 digital channels may be broadcast using the bandwidth previously occupied by one analog channel.

Note:  We recommend that transmitter and antenna be purchased together and components carefully balanced and tuned to optimize output.  This is especially important to get maximum output and avoid unnecessary power losses from low power transmission equipment.

The usual components of a transmitter cabinet are:  

  • Power supply – if well designed can reduce the impact of lightning storms.
  •  Modulator  - Combines audio & video onto single IF frequency output.
  • Frequency Convertor:  Converts IF input to required UHF / VHF frequency for the antenna
  • Power Amplifier: Amplifies signal to required level
  • Filter:  Ensures transmission on the required frequency and avoids interference on adjacent frequencies.  It protects against lightning too.  Otherwise, it makes no difference to signal and can temporarily be bypassed if needed,  for testing

The exact frequency is needed for calibration, which must be done at workshop using specialized instruments.  


5   Feeder Cable
For LPTV transmitters, the feeder cable used is very important, to minimize signal losses.  50 ohm cable is recommended.  For less than 20m,  ½” cable may be used, while for longer distances, 7/8” cable is recommended.   Cables should be properly supported by cable trays and suitable clamps at regular intervals.

6    Antenna
There are various types of antennas.   Each has its own characteristics.  The most common types are Dipoles, Panels and Grids.

The Site Evaluator will establish the sweep or coverage needed in each target area, which could range from less than 180º to a full 360º.  

Consult with your equipment vendor or manufacturer to obtain the right configuration of antennas to efficiently reach your target area.

It is important to match the antenna with the feeder cable and transmitter, in order to optimize the output and avoid unnecessary signal losses.   This is best done by the manufacturer in the factory, using sophisticated measuring equipment.

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For further assistance, write to us at techinfo(at)hopetv(dot)org