|
From which part of the mast are the signals transmitted?
|
In the main from a cylindrical section at the top of the mast, enclosed in weatherproof cover. Incoming signals are sometimes received at the transmitter via large microwave dishes lower down the mast.
photoeverywhere.co.uk/britain/peakspennines/winterhill2327.jpg
|
It depends upon the transmission type.
For example digital TV (freeview) was mostly transmitted by aerials half way up masts or near the top (at low power) until switch over.
Not long before switch over a new transmission aerial is installed at the top and analogue TV still transmitted on these until switch over.
here's an example of Sandy Heath switch over work carried out.
tx.mb21.co.uk/gallery/sandyheath/dso/index.php
so that's TV aerials covered but for lower frequencies like Radio say on medium wave or long wave, then two masts are used and the aerial is hung between them.
This is because the frequencies are lower so the physical size of the aerial grows.
the difference in in aerial size relates to the frequency that is intended to be transmitted.
Hence a transmission frequency of 1.8Mhz is something like 160m aerial needed
and at 144mhz about 1.6m aerial
then at satellite frequencies of around 11ghz it is 1cm aerial.
I hope it explains it without too much geek speak.
|
>> Hence a transmission frequency of 1.8Mhz is something like 160m aerial needed
>> and at 144mhz about 1.6m aerial
>> then at satellite frequencies of around 11ghz it is 1cm aerial.
Tho you don't need a full wave aerial to transmit, at very high power it certainly helps!
|
|
yes your right Zero but I didn't want to confuse matters with full wave, half wave and folded poles. lol
|
I do love my cobweb takes up hardly any room and no need for long wires.
The verticals on the other hand stand out like a sore thumb.
This is the cobweb for those that don't know. www.g3tpw.co.uk/
Last edited by: Bigtee on Tue 20 Mar 12 at 16:55
|
Obviously works, but I question the maths, a dBi is roughly -2.7 dBd.
Halo antennas can be very useful where horizontal polarisation is needed, but the oft seen halo for band 2/VHF/the FM band is usually a poor choice as slant or mixed polarisation means a vertical dipole will return more signal and be cheaper to boot.
|
Not much to add really; radio signals will travel further the higher above the earth's surface the antenna is, so in general the higher up the mast the better.
Lots of photos of hardware on the MB21 site already limked, page 3 of this pdf gives an idea of the size of an antenna array for high power UHF broadcast:-
www.kathrein-scala.com/catalog/hpbcast.pdf
|
Not much to add really; radio signals will travel further the higher above the earth's surface the antenna is, so in general the higher up the mast the better.
Not quite true on VHF/UHF the height is better on HF it will work the world when lower as well some antenna verticals are designed to work from the garden with radials buried in the ground.
|
>> Not much to add really; radio signals will travel further the higher above the earth's
>> surface the antenna is, so in general the higher up the mast the better.
spamcan61 said exactly the same!
:-)
|
He meant to add quote marks... He goes on to modify the point.
The question of aerial height is much more complex than can be addressed here. However it is usual to use the ground as a very large part of the aerial system on HF (read short wave). This combined with angle of radiation differences, and the fact HF makes use of atmospheric reflection results in quite a difference.
Commercial practice on HF though usually has far bigger aerials than most amateurs have room for.
|
>> He meant to add quote marks...
When you click on "Reply to this message", the >> symbols are already there for you. He must have edited them out.
|
>> When you click on "Reply to this message"
I think quite a few people choose not to do it that way; not sure why.
|
>> >> When you click on "Reply to this message"
>>
>> I think quite a few people choose not to do it that way; not sure
>> why.
>>
Me neither.
|
>> He meant to add quote marks... He goes on to modify the point.
>>
>> The question of aerial height is much more complex than can be addressed here. However
>> it is usual to use the ground as a very large part of the aerial
>> system on HF (read short wave). This combined with angle of radiation differences, and the
>> fact HF makes use of atmospheric reflection results in quite a difference.
>>
>> Commercial practice on HF though usually has far bigger aerials than most amateurs have room
>> for.
Fair point, I should've said 'at UHF and above' as that's where my day job is; although from my perspective 50W is high power, not this TV stuff at 100s of KW.
|
>> From which part of the mast are the signals transmitted?
ALL OF THEM
|
>> From which part of the mast are the signals transmitted?
>>ALL OF THEM
Er no.
Only mast radiators and as a rule, they are only used on medium wave. Even then, not all mw aerials are mast radiators, quite a few mw aerials are a length of wire slung between two mast and for these, the mast radiates none of the signal. As far as broadcast is concerned, never on FM or TV.
But if the above is saying, all of the mast is supporting the aerial, well yes, it would fall down if you took the bottom mast section away...
I used to fix TV and radio transmitters when the BBC owned their own.
|
|
it was a joke slidingpillar.... over and out, wilko, roger dodge
|
Radio/television masts. - Meldrew
