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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

No reflector on new TV antenna



 
 
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  #21  
Old May 17th 17, 11:23 AM posted to uk.tech.digital-tv
Brian Gaff
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Posts: 6,505
Default No reflector on new TV antenna

Well of course they did.
I have a group B two stacked parabeam aray in my shed used originally for
hannington from Chessingt9on to obtain different film choices when the itv
regions did in fact screen other films to each other. I also hav an
Antiference log that is 21 to 68 channels but only has 89.5db gain on
average. It is after all just a string of different sized dipoles in anti
pase and those off resonance tend to act parasitically on those that are.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

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wrote in message news
On Wed, 17 May 2017 12:01:29 +0100
David Woolley wrote:
On 17/05/17 11:55,
d wrote:
But I thought the UHF range of Freeview was actually less than that of
the
old PAL broadcasts since the government had sold off part of the
spectrum?


Originally, channels were grouped, so that, for instance, London only
got low numbered channels. As a result, although the total available
frequency range was larger, the range needed in any one place was a lot
smaller.


Are you saying that rooftop antenna centre frequencies varied between
regions?

--
Spud



  #23  
Old May 17th 17, 11:41 AM posted to uk.tech.digital-tv
AnthonyL
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Posts: 148
Default No reflector on new TV antenna

On Wed, 17 May 2017 08:21:30 +0000 (UTC), d wrote:

On Tue, 16 May 2017 18:25:04 +0100
Robin wrote:
On 16/05/2017 16:41,
d wrote:
We just had a new antenna installed on the roof and it doesn't seem to have
a reflector at the base, just some extra elements instead. Is this normal
these days and is it something to do with digital vs analogue TV or just
cost cutting?

Does it look like this?

http://www.labgear.co.uk/wp-content/...original-1.jpg


Very similar except a bit longer.


Probably one of these, have a look at

http://aerialsandtv.com/ and specifically the

http://aerialsandtv.com/atvschoiceofaerials.html#DMlog

I've used these at two awkward locations and they've solved my
reception problems.


--
AnthonyL
  #24  
Old May 17th 17, 01:27 PM posted to uk.tech.digital-tv
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Posts: 264
Default No reflector on new TV antenna

On Wed, 17 May 2017 12:23:15 +0100
"Brian Gaff" wrote:
Well of course they did.
I have a group B two stacked parabeam aray in my shed used originally for
hannington from Chessingt9on to obtain different film choices when the itv
regions did in fact screen other films to each other. I also hav an
Antiference log that is 21 to 68 channels but only has 89.5db gain on
average. It is after all just a string of different sized dipoles in anti
pase and those off resonance tend to act parasitically on those that are.
Brian


So in other words, if you go and buy an antenna yourself instead of getting a
professional to install one, you need to check its centre frequency to see if
it matches your local transmitter? Sounds like a faff. Why don't they just
build them with the centre freq in the middle of the band and add a few
more elements for extra db?

--
Spud

  #25  
Old May 17th 17, 01:44 PM posted to uk.tech.digital-tv
Andy Burns[_12_]
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Posts: 237
Default No reflector on new TV antenna

d wrote:

Are you saying that rooftop antenna centre frequencies varied between regions?


And over time.


  #26  
Old May 17th 17, 02:01 PM posted to uk.tech.digital-tv
Bob Latham
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Posts: 521
Default No reflector on new TV antenna

The author has marked this message not to be archived. This post will be deleted on May 24, 2017.

In article ,
wrote:
On Wed, 17 May 2017 12:23:15 +0100
"Brian Gaff" wrote:
Well of course they did. I have a group B two stacked parabeam aray in
my shed used originally for hannington from Chessingt9on to obtain
different film choices when the itv regions did in fact screen other
films to each other. I also hav an Antiference log that is 21 to 68
channels but only has 89.5db gain on average. It is after all just a
string of different sized dipoles in anti pase and those off resonance
tend to act parasitically on those that are.
Brian


So in other words, if you go and buy an antenna yourself instead of
getting a professional to install one, you need to check its centre
frequency to see if it matches your local transmitter? Sounds like a
faff. Why don't they just build them with the centre freq in the middle
of the band and add a few more elements for extra db?


Aerials used to be coloured coded (the plastic bung in each end) to tell
you which group they were suitable for. The groups used to be A,B,CD but
there were other variants that covered overlap. The wiser the bandwidth of
the aerial the less gain it had for a given size.

Where I live it used to be that
The Wrekin was/is group A,
Sutton Coldfield was/is group B
Brierley Hill was/is CD.

Bob.

  #27  
Old May 17th 17, 02:19 PM posted to uk.tech.digital-tv
Mark Carver[_2_]
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Posts: 252
Default No reflector on new TV antenna

On 17/05/2017 14:27, d wrote:

So in other words, if you go and buy an antenna yourself instead of getting a
professional to install one, you need to check its centre frequency to see if
it matches your local transmitter? Sounds like a faff.


It worked fine.

There were three main groups.

Group A that covered Ch 21-34

Group B that covered Ch 39-53

Group C/D that covered Ch 48-68 (replaced Groups C and D that covered
smaller ranges within 48-68)

The four channel analogue plan for a given transmitter was normally (90%
of cases) in one of the nine following clusters:-

21,24,27,31
22,25,28,32 Group A
23,26,29,33

39,42,45,49
40,43,46,50 Group B
41,44,47,51

53,57,60,63
54,58,61,64 Group C/D
55,59,62,65


Then there were other transmitters that used non standard channel
allocations, usually not anything that was out of one of the three
aerial groups.

For instance Dover 50, 53, 56, 66

In some exceptional cases, groups were straddled, the biggest affected
transmitter (in terms of coverage) was Hannington

39,42,45,66

In that case Group E was specified, Ch 39-68. Group E aerials
were rare to find, even in the affected areas. Often instead Widebands
had to be used (21-68)

Once C5 and then DTT came along, the whole plan fell apart in many
areas, as anything empty from 21 to 68 was used.

However, at DSO, in most cases three out of the original four analogue
assignments were used for PSB 1,2 and 3, to ensure anybody still with a
legacy grouped aerial received core services.

What fell out of use at DSO were UHF Ch 61-68.

Between this year and 2020, Ch 49-60 will be going (although there's
talk of Ch 55 and 56 being retianed until 2022 for COM 7 and 8).

Why don't they just
build them with the centre freq in the middle of the band and add a few
more elements for extra db?


If you add elements, you increase gain but at the expence of bandwidth.



--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #28  
Old May 17th 17, 03:10 PM posted to uk.tech.digital-tv
David Woolley[_2_]
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Posts: 514
Default No reflector on new TV antenna

On 17/05/17 15:19, Mark Carver wrote:
If you add elements, you increase gain but at the expence of bandwidth.



Also remember that the UHF TV allocation was very large. For good
resonance, you want element length to be within a few percent of the
theoretical value, but doing what you suggest would require the antenna
to work 25% off resonance. That is huge for a resonant system. Even
the original groupings were probably pushing things to the limit.
 




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