A Home cinema forum. HomeCinemaBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » HomeCinemaBanter forum » Home cinema newsgroups » UK digital tv
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Is there an atmospheric lift on as at 20.18 hrs 15th August 2018??



 
 
Thread Tools Display Modes
  #1  
Old August 15th 18, 08:20 PM posted to uk.tech.digital-tv
[email protected]
external usenet poster
 
Posts: 95
Default Is there an atmospheric lift on as at 20.18 hrs 15th August 2018??

I've pretty much lost all freeview reception from Sandy Heath, Oxford, Sutton Coldfield and Waltham.

The spectrum analyser shows all muxes present at the expected signal levels but all TV sets are reporting almost zero quality on all muxes.

My Location is Northampton.....
  #4  
Old August 16th 18, 07:39 AM posted to uk.tech.digital-tv
[email protected]
external usenet poster
 
Posts: 95
Default Is there an atmospheric lift on as at 20.18 hrs 15th August 2018??

The one common denominator then linking the TV aerials to all the TV sets would be the multiswitches.

Freesat and the analogue CCTV was fine though......

Interestingly enough, I had to swap out one of the televes avant 5 to another unit as there was a single spike at around 110 dBuV at exactly 629 MHz. This unit processes the sandy heath and Waltham signals. This spike was not an issue for the sandy heath or Waltham muxes...

It became an issue when the output of this was combined with one of the other Avant 5 that processes the Oxford and Sutton Coldfield signals as this 629 MHz spike was then sat on top of Ch 40 from Sutton Coldfield thereby wrecking it.

What I did notice on the spectrum analyser was that all of the muxes appeared to be missing carriers so they looked like an upside down comb instead of a solid block of parallel carriers if that makes sense?
  #5  
Old August 20th 18, 09:41 PM posted to uk.tech.digital-tv
[email protected]
external usenet poster
 
Posts: 95
Default Is there an atmospheric lift on as at 20.18 hrs 15th August 2018??

On Thursday, 16 August 2018 07:39:05 UTC+1, wrote:
The one common denominator then linking the TV aerials to all the TV sets would be the multiswitches.

Freesat and the analogue CCTV was fine though......

Interestingly enough, I had to swap out one of the televes avant 5 to another unit as there was a single spike at around 110 dBuV at exactly 629 MHz.. This unit processes the sandy heath and Waltham signals. This spike was not an issue for the sandy heath or Waltham muxes...

It became an issue when the output of this was combined with one of the other Avant 5 that processes the Oxford and Sutton Coldfield signals as this 629 MHz spike was then sat on top of Ch 40 from Sutton Coldfield thereby wrecking it.

What I did notice on the spectrum analyser was that all of the muxes appeared to be missing carriers so they looked like an upside down comb instead of a solid block of parallel carriers if that makes sense?



All sorted now... I did an autolevel on both Avants to try and sort it out but the output signal levels were all over the place and some muxes were missing at the outputs despite the unit telling me there was sufficient input signal for the missing muxes.

I went for the mains lead pulling option, waited 60 seconds, replugged the mains leads back in, did the autolevel again on both units, and all the missing muxes are now back and at the correct output signal levels.!
  #6  
Old January 1st 19, 12:37 AM posted to uk.tech.digital-tv
[email protected]
external usenet poster
 
Posts: 95
Default Is there an atmospheric lift on as at 20.18 hrs 15th August 2018??

Update....

The problem came back. So did some further investigation.

Turns out the masthead amp for the Sutton Coldfield aerial was oscillating along with some intermittent spikes.

This was causing one of the 3 Avant 5's to decrease and increase gain constantly in its battle to try and keep the output at 111dBuV....

I have now replaced said masthead amp and it's now fine.

What I found interesting was that Despite the 4g filter before AND after the Sutton coldfield masthead amp, and then being filtered by an Avant 5, to leave just 6 group B channels, some of the cctv channels 60, 62 and 64 were being affected by the errant masthead amp.

The cctv channels are mostly in group C/D and processed by another Avant 5 before being combined with the rest of the Avant 5s.

  #8  
Old January 1st 19, 10:07 AM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 3,490
Default Is there an atmospheric lift on as at 20.18 hrs 15th August2018??

On 01/01/2019 07:52, Brian Gaff wrote:
I've never heard of one going into oscillation. perhaps a spider got in and
was adding positive feeddback between input and output as it decomposed!
grin.
Brian

They do oscillate. It can cause a lot of interference to surrounding
aerials, especially as field strength is likely to be weak so there is
great susceptibility to interference of all kinds.

The oscillation can be intermittent, and can drift. It can be in-band or
out-of-band. Radiation is usually via the aerial the amp is connected to.

Small domestic distribution amps can oscillate. They can feed a strong
carrier back into the input feeder. These amps are often used to provide
extra feeds in a property where the aerial feed comes from a
distribution system. In that case they can wipe out reception in the
whole block. The carrier doesn't get into the input stages of the
head-end amps, fortunately. It merely gets into other downleads, so it
usually only causes a problem if it coincides with a mux. Usually it's
possible to 'tune' the carrier by putting a hand on the amp casing or
touching a connector.

Hypothetically,it would be possible to generate a strong carrier that
might wipe out all terrestrial reception in the area, by making an amp
oscillate. It could be done very easily as follows, I suppose. Connect
the output of a masthead amp to a splitter. One leg of the splitter to
feed back into the amp input, via a simple tuned circuit (a). The other
leg of the splitter to feed a high gain distribution amp (or daisy-chain
of amps) via another tuned circuit (b). The output of the final amp to
feed an aerial. (a) allows the carrier to be tuned. (b) merely reduces
noise from the masthead amp to be attenuated, thus allowing the output
amps to operate more efficiently. If the output amp is actually two or
more daisy-chained this filter could go between two of them. I suppose
if (a) is in a case and the case affects the tuning, loosening the
screws and then shouting at it will provide FM modulation!

Happy New Year

Bill
  #9  
Old January 2nd 19, 09:51 AM posted to uk.tech.digital-tv
Brian Gaff
external usenet poster
 
Posts: 7,742
Default Is there an atmospheric lift on as at 20.18 hrs 15th August 2018??

Hmm, well it might actually be why some videos tended to create interference
but that was more likely to be cross mod in the amp inside.

I don't think an oscillating amp would be stable enough to be used as a
transmitter!
I did use a signal generator as a tv transmitter once when I was young and
foolish and everything was on VHF.
Brian

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

Blind user, so no pictures please
Note this Signature is meaningless.!
"Bill Wright" wrote in message
...
On 01/01/2019 07:52, Brian Gaff wrote:
I've never heard of one going into oscillation. perhaps a spider got in
and
was adding positive feeddback between input and output as it decomposed!
grin.
Brian

They do oscillate. It can cause a lot of interference to surrounding
aerials, especially as field strength is likely to be weak so there is
great susceptibility to interference of all kinds.

The oscillation can be intermittent, and can drift. It can be in-band or
out-of-band. Radiation is usually via the aerial the amp is connected to.

Small domestic distribution amps can oscillate. They can feed a strong
carrier back into the input feeder. These amps are often used to provide
extra feeds in a property where the aerial feed comes from a distribution
system. In that case they can wipe out reception in the whole block. The
carrier doesn't get into the input stages of the head-end amps,
fortunately. It merely gets into other downleads, so it usually only
causes a problem if it coincides with a mux. Usually it's possible to
'tune' the carrier by putting a hand on the amp casing or touching a
connector.

Hypothetically,it would be possible to generate a strong carrier that
might wipe out all terrestrial reception in the area, by making an amp
oscillate. It could be done very easily as follows, I suppose. Connect the
output of a masthead amp to a splitter. One leg of the splitter to feed
back into the amp input, via a simple tuned circuit (a). The other leg of
the splitter to feed a high gain distribution amp (or daisy-chain of amps)
via another tuned circuit (b). The output of the final amp to feed an
aerial. (a) allows the carrier to be tuned. (b) merely reduces noise from
the masthead amp to be attenuated, thus allowing the output amps to
operate more efficiently. If the output amp is actually two or more
daisy-chained this filter could go between two of them. I suppose if (a)
is in a case and the case affects the tuning, loosening the screws and
then shouting at it will provide FM modulation!

Happy New Year

Bill



  #10  
Old January 2nd 19, 10:19 AM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 1,684
Default Is there an atmospheric lift on as at 20.18 hrs 15th August 2018??

"Brian Gaff" wrote in message
...
Hmm, well it might actually be why some videos tended to create
interference but that was more likely to be cross mod in the amp inside.

I don't think an oscillating amp would be stable enough to be used as a
transmitter!
I did use a signal generator as a tv transmitter once when I was young and
foolish and everything was on VHF.


I did that with my signal generator on AM many years ago: I set it to 198
kHz and fed in audio from a tape to the AM input and was able to pick up
that audio on a radio, drowning out R2 (as it was in those days on that
frequency). It was done as part of a test - once I proved that it worked, I
stopped in case the neighbours complained that someone had hijacked Jimmy
Young :-)

 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
2018 Q1 700 MHz Clearance details Mark Carver[_2_] UK digital tv 129 December 5th 17 01:20 AM
Ladies & Gentlemen, there is a 'lift' on! Marky P UK digital tv 9 January 16th 05 12:36 PM
More atmospheric trouble with Rowridge mux 2 (ch 52) ITV, Ch4 etc Roger UK digital tv 7 September 16th 04 12:29 PM
[LOCAL] TiVo hacking presentation, Davis Calif, Sept. 15th William Kendrick Tivo personal television 2 September 11th 03 09:05 AM
Columbia, SC Locals on July 15th DodgeThunder Satellite dbs 0 July 11th 03 06:55 PM


All times are GMT +1. The time now is 05:57 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright 2004-2019 HomeCinemaBanter.
The comments are property of their posters.