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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.

New aerial for Winter Hill.



 
 
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  #1  
Old January 29th 18, 11:31 PM posted to uk.tech.digital-tv
Graham.[_12_]
external usenet poster
 
Posts: 472
Default New aerial for Winter Hill.

I will be overhauling my aerials when the weather gets a bit warmer
and I was wondering, after the 700MHz band clearance and move
downwards, what group of aerial to use rather than the C/D one I have
now that is already sub-prime.

We were promised a new grouping scheme optimised for the post 800Mhz
clearance, did the manufactures deliver this?

What about the even smaller band we are about to get, has that
influenced the aerials available, or is there now just one group?
--

Graham.
%Profound_observation%
Ads
  #3  
Old January 30th 18, 12:25 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 2,448
Default New aerial for Winter Hill.

On 30/01/2018 09:24, Brian Gaff wrote:
I'd imagine any new aerial will be a log and be a smaller bandwidth one than
the old days.
Brian

It seems likely.

Bill
  #4  
Old January 30th 18, 12:30 PM posted to uk.tech.digital-tv
Woody[_5_]
external usenet poster
 
Posts: 1,865
Default New aerial for Winter Hill.


"Graham." wrote in message
...
I will be overhauling my aerials when the weather gets a bit warmer
and I was wondering, after the 700MHz band clearance and move
downwards, what group of aerial to use rather than the C/D one I
have
now that is already sub-prime.

We were promised a new grouping scheme optimised for the post 800Mhz
clearance, did the manufactures deliver this?

What about the even smaller band we are about to get, has that
influenced the aerials available, or is there now just one group?
--



If you have a good strong signal then your best bet is a log periodic
as they are essentially flat response.

On the other hand if your signal requires a longer yagi or multibeam
now then - sadly - your best bet is a wideband multibeam. You can fit
an in-line 790MHz filter now if you feel it necessary and change that
to a 700MHz fliter after clearance has been completed. Such a filter
is definitely a good idea if you have any form of wideband preamp to
prevent overloading by out-of-band signals.

Filters widely available quite cheaply on fleabay.


--
Woody

harrogate3 at ntlworld dot com


  #5  
Old January 30th 18, 06:30 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 2,448
Default New aerial for Winter Hill.

On 30/01/2018 13:30, Woody wrote:

If you have a good strong signal then your best bet is a log periodic
as they are essentially flat response.

On the other hand if your signal requires a longer yagi or multibeam
now then - sadly - your best bet is a wideband multibeam.


However the gain of these will be similar or worse than a log on the
lower channels, and the directivity will be far worse on those channels.

You can fit
an in-line 790MHz filter now if you feel it necessary and change that
to a 700MHz fliter after clearance has been completed. Such a filter
is definitely a good idea if you have any form of wideband preamp to
prevent overloading by out-of-band signals.

Filters widely available quite cheaply on fleabay.


But only buy a known brand.

Bill



  #6  
Old January 30th 18, 07:24 PM posted to uk.tech.digital-tv
Brian Gaff
external usenet poster
 
Posts: 7,250
Default New aerial for Winter Hill.

Actually many logs had a slightly rising gain with frequency to compensate
for losses due to the higher frequencies.

Brian

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

Blind user, so no pictures please!
"Woody" wrote in message
news

"Graham." wrote in message
...
I will be overhauling my aerials when the weather gets a bit warmer
and I was wondering, after the 700MHz band clearance and move
downwards, what group of aerial to use rather than the C/D one I have
now that is already sub-prime.

We were promised a new grouping scheme optimised for the post 800Mhz
clearance, did the manufactures deliver this?

What about the even smaller band we are about to get, has that
influenced the aerials available, or is there now just one group?
--



If you have a good strong signal then your best bet is a log periodic as
they are essentially flat response.

On the other hand if your signal requires a longer yagi or multibeam now
then - sadly - your best bet is a wideband multibeam. You can fit an
in-line 790MHz filter now if you feel it necessary and change that to a
700MHz fliter after clearance has been completed. Such a filter is
definitely a good idea if you have any form of wideband preamp to prevent
overloading by out-of-band signals.

Filters widely available quite cheaply on fleabay.


--
Woody

harrogate3 at ntlworld dot com



  #7  
Old January 30th 18, 10:51 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 2,448
Default New aerial for Winter Hill.

On 30/01/2018 20:24, Brian Gaff wrote:
Actually many logs had a slightly rising gain with frequency to compensate
for losses due to the higher frequencies.

Brian

I don't know how that could be achieved Brian. The gain of a log is set
by the tau factor, which can't vary along the boom.

Bill
  #8  
Old January 31st 18, 05:20 PM posted to uk.tech.digital-tv
R. Mark Clayton[_2_]
external usenet poster
 
Posts: 649
Default New aerial for Winter Hill.

On Tuesday, 30 January 2018 23:51:15 UTC, wrote:
On 30/01/2018 20:24, Brian Gaff wrote:
Actually many logs had a slightly rising gain with frequency to compensate
for losses due to the higher frequencies.

Brian

I don't know how that could be achieved Brian. The gain of a log is set
by the tau factor, which can't vary along the boom.

Bill


I think it might depend on which end the cable is connected. Usually it is the large low frequency end, but some have the connection at the short high frequency end.
  #9  
Old January 31st 18, 05:53 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 2,448
Default New aerial for Winter Hill.

On 31/01/2018 18:20, R. Mark Clayton wrote:
On Tuesday, 30 January 2018 23:51:15 UTC, wrote:
On 30/01/2018 20:24, Brian Gaff wrote:
Actually many logs had a slightly rising gain with frequency to compensate
for losses due to the higher frequencies.

Brian

I don't know how that could be achieved Brian. The gain of a log is set
by the tau factor, which can't vary along the boom.

Bill


I think it might depend on which end the cable is connected. Usually it is the large low frequency end, but some have the connection at the short high frequency end.

No, the cable has to be connected at the HF end. That's fundamental to
the operation of the aerial. What you've seen is examples where there's
an internal feeder from one end to the other.

To explain in a bit more detail, for a given frequency only a small zone
along the boom of the log periodic is active. The zone is centred on the
dipoles that are at or near resonance at that frequency. Consider two
adjacent dipoles, somewhere about half way along the boom. The incoming
signal is in the middle of the frequency range of the aerial, so the two
dipoles are approximately resonant and are therefore in the active zone.
Feeder reversal and the distance between the two elements gives a phase
shift of 360° between them. In other words, for a signal coming from the
‘front’ of the aerial (only) the signal on the two dipoles is additive
if it is collected from the front of the boom-cum-transmission line.
This is why log periodics are directional, and why the feed-point is at
the sharp end. It’s possible for three or even four dipoles to work
together in this way. A smaller ratio between the lengths of adjacent
dipoles means more dipoles are near resonance for a particular
frequency, which is why the gain is higher for such an aerial. There are
two things that prevent the dipoles that are shorter and longer than the
resonant ones from playing much of a part in reception. One is that they
aren’t resonant and the other is that the spacing between them does not
produce the 360° of phase shift that is essential for the aerial to have
gain and directivity. The spacing between the directors on a yagi can be
varied widely (and often is to help feeder matching) but with a log
periodic the spacing has to be much more closely defined, and has to
take into account the velocity factor of the twin booms.

Bill
  #10  
Old February 1st 18, 11:37 AM posted to uk.tech.digital-tv
R. Mark Clayton[_2_]
external usenet poster
 
Posts: 649
Default New aerial for Winter Hill.

On Wednesday, 31 January 2018 18:53:54 UTC, wrote:
On 31/01/2018 18:20, R. Mark Clayton wrote:
On Tuesday, 30 January 2018 23:51:15 UTC, wrote:
On 30/01/2018 20:24, Brian Gaff wrote:
Actually many logs had a slightly rising gain with frequency to compensate
for losses due to the higher frequencies.

Brian

I don't know how that could be achieved Brian. The gain of a log is set
by the tau factor, which can't vary along the boom.

Bill


I think it might depend on which end the cable is connected. Usually it is the large low frequency end, but some have the connection at the short high frequency end.

No, the cable has to be connected at the HF end. That's fundamental to
the operation of the aerial. What you've seen is examples where there's
an internal feeder from one end to the other.

To explain in a bit more detail, for a given frequency only a small zone
along the boom of the log periodic is active. The zone is centred on the
dipoles that are at or near resonance at that frequency. Consider two
adjacent dipoles, somewhere about half way along the boom. The incoming
signal is in the middle of the frequency range of the aerial, so the two
dipoles are approximately resonant and are therefore in the active zone.
Feeder reversal and the distance between the two elements gives a phase
shift of 360° between them. In other words, for a signal coming from the
‘front’ of the aerial (only) the signal on the two dipoles is additive
if it is collected from the front of the boom-cum-transmission line.
This is why log periodics are directional, and why the feed-point is at
the sharp end. It’s possible for three or even four dipoles to work
together in this way. A smaller ratio between the lengths of adjacent
dipoles means more dipoles are near resonance for a particular
frequency, which is why the gain is higher for such an aerial. There are
two things that prevent the dipoles that are shorter and longer than the
resonant ones from playing much of a part in reception. One is that they
aren’t resonant and the other is that the spacing between them does not
produce the 360° of phase shift that is essential for the aerial to have
gain and directivity. The spacing between the directors on a yagi can be
varied widely (and often is to help feeder matching) but with a log
periodic the spacing has to be much more closely defined, and has to
take into account the velocity factor of the twin booms.

Bill


Thanks for clearing that up. Pictures mostly show the mount and feed at the [heavy] low frequency end.
 




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