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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.

Crystal Palace Issues



 
 
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  #71  
Old April 5th 18, 06:27 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Default Crystal Palace Issues

On 05/04/2018 19:17, Andy Burns wrote:
Andy Burns wrote:

"typical" 48 element LP?


I can't see anyone selling LP with that many elements ...


Even Blake are in two minds about the "double elements" on their LP36T


Total **** up really, that web page.

Bill
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  #72  
Old April 5th 18, 06:36 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Default Crystal Palace Issues

On 05/04/2018 19:27, Andy Burns wrote:
Bill Wright wrote:

since marketing men always over-rule engineers the
modern products have names that exaggerate the element count by a factor
of two, because they count each half of each dipole as one!


Ah I didn't realise my DML26 only has 13 elements ...


It might, if you accept the various manufacturers' underhanded and
misleading nomenclature, be said to have 26 elements. But it only has 13
dipoles. That's if you accept that the aerial's fundamental principle of
operation is based on the phase relationships between its half-wave
dipoles, each of which is composed of two quarter wave 'elements'.

Bill
  #73  
Old April 5th 18, 08:01 PM posted to uk.tech.digital-tv
pinnerite
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Default Crystal Palace Issues

Following this thread and checking elsewhere I realised that I would have to
bite the bullet.

We are 30 km from Crystal Palace and 225 ft above sea level according the
Ordnance survey map I bought 45 years ago. It was in 1975 that I swapped my
chicken wire loft aerial for a real one. Well, three actually. One was aimed
at the 'Palace', one towards Sandy in Beds and one towards Southern. That
way, at the time we often got a choice of more than three broadcasts.

when 'digital'came along they all came down, replaced by a slender job from
which the local pigeons and seagulls would cap all over our front step.

I had anticipated one of the Labgear 450 jobs because of the high forward
gain. Instead the local installer fitted a £30 Antiference job. I must say
it seems t do the job but including VAT it came to £156. Don't you just love
the cost of progress.

--
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KDE version 4.14.5 on an AMD Phenom II X4 Black edition.

  #75  
Old April 6th 18, 06:34 PM posted to uk.tech.digital-tv
charles[_2_]
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Default Crystal Palace Issues

In article , Bill Wright
wrote:
On 30/03/2018 14:36, John wrote:
I dutifully retuned, and was shocked to find a load of channels
missing! Especially annoying was the loss of BBC News HD and BBC Four
HD.



I live in a Central London tower block and have my own Group A aerial
pointing at Crystal Palace/Croydon at rooftop level and a 70m cable run
down to my living room.


The obvious thing would be to remove the existing Group A aerial and
replace it with a Group W one. However, I worry about its lesser
sensitivity at the Group A end.


If you are in central London you will be swamped with CP signal,


at IBC in Grosvenor House, Park Lane, (mid 70s) a roof aerial and 100m of
cable still needed a 20dB attenuator so that the prototype Ceefax set could
work.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
  #76  
Old April 7th 18, 12:11 AM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 2,448
Default Crystal Palace Issues

On 06/04/2018 19:34, charles wrote:

at IBC in Grosvenor House, Park Lane, (mid 70s) a roof aerial and 100m of
cable still needed a 20dB attenuator so that the prototype Ceefax set could
work.


In the analogue days I always felt it necessary to use a decent 18
element grouped yagi in central London because of the multipath from the
big buildings. This would produce something like 35 to 40dBmV.

100m of good cable would drop the level to 20 to 25dBmV. This would
certainly need attenuation for a 70s Ceefax telly. 20dB sounds about right.

Seventies Ceefax sets were very critical of signal level and quality.
These sets often couldn't handle signal levels above 10dBmV. Many had a
screwdriver operated variable attenuator in the rear panel next to the
preset tuning knobs. If there wasn't a attenuator DER and Radio Rentals
expected me to supply one at no charge, which I certainly wasn't going
to do because margins were very lean.

Some aerial installers used to put a one-strand short circuit in the
coax plug. Being a more sophisticated sort of chap I used to make two
Faraday loops and close couple them.

Poor VSWR, reflections on the cable, ghosting, etc, were killers for
Ceefax. Bad cable joints, splitters etc, would stop Ceefax.

Sometimes the Ceefax would only work with the AGC turned off and the set
detuned very slightly! The AGC was often linked to the hinge on the door
of the tuning knobs but this was easily defeated...

Bill
  #77  
Old April 12th 18, 10:58 AM posted to uk.tech.digital-tv
[email protected]
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Posts: 46
Default Crystal Palace Issues

On Tue, 3 Apr 2018 08:37:29 -0700 (PDT), John
wrote:

On Friday, 30 March 2018 19:16:03 UTC+1, wrote:
On 30/03/2018 14:36, John wrote:
I dutifully retuned, and was shocked to find a load of channels missing! Especially annoying was the loss of BBC News HD and BBC Four HD.



I live in a Central London tower block and have my own Group A aerial pointing at Crystal Palace/Croydon at rooftop level and a 70m cable run down to my living room.


The obvious thing would be to remove the existing Group A aerial and replace it with a Group W one. However, I worry about its lesser sensitivity at the Group A end.


If you are in central London you will be swamped with CP signal, even
allowing for beam tilt (tx looks downwards a bit).


Just a moment ago, the aerial chappie sent by Digital TV did some readings in my living room with his bright yellow meter reader. No issues with the Group A end, and zero reading at 55 and 56.

We went to the roof and with a glance, he confirmed what I told him, ie that I had a Group A aerial.

He made me sign a form and will tell his firm to send two guys to swap out my Group A and replace it with a Group W. No charge to me! Yippee!


Interesting! I had a different experience when I contacted the
Freeview advice line on 0808 100 0288 I was ask what the probem was. I
said that since the retune and the move to 56 I could no long receive
various stations, in particular Freesport. Took my details, but then
ask me whether I had cable or Sky? I obviously gave the wrong answer,
I said yes, Virgin. I should have said, no. Yes, was the turn off. I
was told they could not help me. The fact that Virgin did not carry
Freesport and the only way I could receive was via Freeview didn't
count and I would to have a new aerial installed at my own cost.

Ah well.

--
Pete

 




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