Are digital TV transmitter aerials omnidirectional?

[Dave2002]

Clearly TV aerials for receivers are often directional. I wondered if digital TV transmitter aerials are also directional.
If they are well in land, they might as well be omni-directional if the receiving population are evenly distributed around the transmitter, but if they are near the coast there's perhaps not much point in having omni-directional broadcasting - that would be a waste of energy if there's no intention to broadcast to shipping. If they are directional, what technology is used?

I know that mobile phone transmitters can beam fairly precisely in specific directions, and also that the beams can be reshaped according to schedules, but there is also an interaction between the phones and the mobile phone masts, but broadcast TV does not have a 2-way interaction between the receiver and the transmitter.

[Anastasius]

The answer is 'Yes'..."transmitter radiation pattern' is your Google term (other search engines are available).

http://www.aerialsandtv.com/nationwidetransmitters.html#TransmitterRadiationPatterns

[Quarky]

This is the Crystal Palace Transmitter in close up: http://tx.mb21.co.uk/gallery/crystal...palace-pb2.php

And this is a more up to date picture: http://tx.mb21.co.uk/gallery/crystal...l-palace10.php

it looks as though it has banks of directional antennas to produce an omnidirectional pattern. The huge white column appears to be the main antenna , and looks as though it is composed of arcuate section antennas creating an overall omni pattern.

200KW - wow!

[Old Grumpy]

This is the Crystal Palace Transmitter in close up: http://tx.mb21.co.uk/gallery/crystal...palace-pb2.php

And this is a more up to date picture: http://tx.mb21.co.uk/gallery/crystal...l-palace10.php

it looks as though it has banks of directional antennas to produce an omnidirectional pattern. The huge white column appears to be the main antenna , and looks as though it is composed of arcuate section antennas creating an overall omni pattern.

200KW - wow!

WOW, indeed!

And I am called an anorak by Mrs G for subscribing to Radio Listeners' Guide...


Mr Bigwood must be one helluva'n anorak


OG

I'll get my flask...

[Dave2002]

The answer is 'Yes'..."transmitter radiation pattern' is your Google term (other search engines are available).

http://www.aerialsandtv.com/nationwi...iationPatterns

Interesting site that. One worrying thing is the comment in one of the pages - either there or on the ones about the other transmitters, such as Crystal Palace - that even if one is notionally within the coverage area, the beam pattern may be set up to not reach out to potential users. I recently bought a new TV aerial with the intention of trying to find a difficult to locate beam - plus a signal detector - and now I'm not even sure that the aerial itself works. The detector does - I did just manage to trigger it once with a different aerial with amplification, but now I might have to resort to driving round with the aerial in my car until I can find a spot near the transmitters in order to check that I haven't been sold a dud!

The graphic showing how some repeaters managed to cover a greater area than the main transmitter, plus comments about reception in the Sheffield area is interesting. Maybe that explains a few things - hills are sometimes a darned nuisance. The fact that there may be repeaters which are relatively close to the endpoint, indicates that it may be possible to get reception from quite distant transmitters, but presumably the repeaters are (a) sited in fairly good areas for reception, (b) similarly for local retransmission, and (c) use amplification and antennae which most domestic users would not consider.

Do the repeaters simply take the incoming signal, and rebroadcast on a different (maybe even the same?) set of frequencies, or do they decode the data, and then recode and retransmit?