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UHF home distribution and witchcraft



 
 
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  #51  
Old August 26th 19, 03:19 PM posted to uk.tech.digital-tv
Terry Casey[_2_]
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Posts: 965
Default UHF home distribution and witchcraft

In article ,
says...

On 24/08/2019 18:08, Bob Latham wrote:



To me this proves categorically that this problem is nothing to do
with Humax and Sony boxes, Sky boxes, Sky link+ boxes splitters and
combiners because none of them were in circuit.

So now you bypass the amp.


My sentiments entirely.

Obviously there is more than enough signal on the amp input to
drive one set. Try a 6db pad in the feed and try it on all
threee sets in turn. If they perform satisfactorily, replace
the amplifier with a three way splitter as a temorary fix.

My guess is that there is a PSU fault in the amplifier or in
the power distribution - probably an electrolytic capacitor
has developed a high ESR or a small value decoupler has gone
o/c.

Take a look inside, especially the electrolytics. Look
carefully for any sign that the can of one (or more)of them is
bulging, creating a rounded effect to the base.

If you find one, replace it - better still, replace all of
them. They quite likely came from the same manufacturer if not
the same batch.

No doubt the PSU runs very hot. Check the temperature rating
on the cans and, if possible, find replacements with a higher
rating.

It goes without saying that they must be specified to have a
low ESR but most are these days, anyway.

If this a bit over your heasd, try one of the vintage forums
such as Golborne Vintage Radio:

https://golbornevintageradio.co.uk

Your amp may not be vintage but TV collections of any age need
some sort of distribution system.

We're a friendly bunch with varying skill levels - our latest
recruit is a 12 year old girl who astounded me, and others I'm
sure, with her level of technical competence learned from her
late father - while many of us are old farts in our 70s and
80s!

--

Terry

---
This email has been checked for viruses by AVG.
https://www.avg.com

  #52  
Old August 26th 19, 04:15 PM posted to uk.tech.digital-tv
Ian Jackson[_7_]
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Posts: 273
Default UHF home distribution and witchcraft

In message , Bill Wright
writes
On 26/08/2019 12:30, Terry Casey wrote:

We pulled the centr dielectric out of the old plug and found
that, when the cable was prepped, the last eight of an inch or
so of foil screen had been ripped off.
Very weird.

A similar one, and I've had it more than once: A microscopically thin
turning of brass, almost invisible to the eye, gets lodged between the
body and the inner. It's possible to look into the mouth of the plug
and not see this.

I once had problems with the cable stripper leaving a thin,
very-hard-to-see film of dielectric on the inner.
--
Ian
  #53  
Old August 26th 19, 06:39 PM posted to uk.tech.digital-tv
[email protected]
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Posts: 122
Default UHF home distribution and witchcraft

Come to think of it, do these tvlinks work backwards through a passive splitter?

I have no experience of these TV links at all.

Let's say the OP manages to get all his Freeview and digital modulators at 60dBuV before that final amp, he could passively split this 8 ways and the output signal would be at 50 dBuV which is still above the required 40dBuV required at the TV set even allowing for cable losses.

That reduces the noise introduced by the last amp and no derating is needed and another PSU removed from the system.
  #54  
Old August 26th 19, 06:48 PM posted to uk.tech.digital-tv
[email protected]
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Posts: 122
Default UHF home distribution and witchcraft

I've just realised that the TV link has to provide power to all the magic eyes so a DC inserter would be needed and a PSU too. So that means the 8 way splitter would also need to pass DC too.....
  #55  
Old August 26th 19, 07:59 PM posted to uk.tech.digital-tv
Bob Latham
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Posts: 747
Default UHF home distribution and witchcraft

The author has marked this message not to be archived. This post will be deleted on September 9, 2019.

In article ,
Terry Casey wrote:
In article ,
says...


So now you bypass the amp.


My sentiments entirely.


Obviously there is more than enough signal on the amp input to
drive one set. Try a 6db pad in the feed and try it on all
threee sets in turn. If they perform satisfactorily, replace
the amplifier with a three way splitter as a temorary fix.


Unfortunately, I can't really do that because the distribution amp
also provides DC power and a return path for the magic eyes at each
of the 6 TVs.

My guess is that there is a PSU fault in the amplifier or in
the power distribution - probably an electrolytic capacitor
has developed a high ESR or a small value decoupler has gone
o/c.


I'm glad you said that. I've just looked up the original purchase -
August 2016, that's 13 years 24/7. I notice that the same device now
has 4G filtering, mine does not.

In the recent past I tried a labgear 8 way dist amp with DC etc. but
I just could not get the magic eyes to work with it. Plus that unit
had F cons and my original amp is belling lee. So rather than change
the plugs for a test I got some convertors but they were difficult to
screw in enough to be firm. A couple broke the f con on the amp in
the attempt. Not well made.

Because of the age of my unit, this fault and the need for a spare I
decided to get a new distribution amp. I've purchased the same again
with 4G filter, it has belling plugs and the remote return should
work. 25 from Amazon. Fingers crossed.

Take a look inside, especially the electrolytics. Look
carefully for any sign that the can of one (or more)of them is
bulging, creating a rounded effect to the base.


If you find one, replace it - better still, replace all of
them. They quite likely came from the same manufacturer if not
the same batch.


With it out of service I will be able to have a good at it, as you
suggest. Of course if the new one is the same....

No doubt the PSU runs very hot.


It is warm yes. It is screwed to the wall near the ceiling in an
under stairs cupboard. Heat seems to get trapped in there above the
height of the door frame.

Check the temperature rating
on the cans and, if possible, find replacements with a higher
rating.


It goes without saying that they must be specified to have a
low ESR but most are these days, anyway.


I'll hopefully get to look next week, just hope a new one fixes the
issue.

[Snip]


Cheers and thanks,

Bob.

--
Bob Latham
Stourbridge, West Midlands
  #56  
Old August 27th 19, 09:42 AM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
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Posts: 4,567
Default UHF home distribution and witchcraft

In article , Bob Latham
wrote:

I'm glad you said that. I've just looked up the original purchase -
August 2016, that's 13 years 24/7. I notice that the same device now has
4G filtering, mine does not.


I guess the above is a typo and you mean 2006!

In the recent past I tried a labgear 8 way dist amp with DC etc. but I
just could not get the magic eyes to work with it. Plus that unit had F
cons and my original amp is belling lee. So rather than change the plugs
for a test I got some convertors but they were difficult to screw in
enough to be firm. A couple broke the f con on the amp in the attempt.
Not well made.


Because of the age of my unit, this fault and the need for a spare I
decided to get a new distribution amp. I've purchased the same again
with 4G filter, it has belling plugs and the remote return should work.
25 from Amazon. Fingers crossed.


This is an awkward time to buy something wrt 4G filtering. The question
which the above brought to my mind is: Does it filter 700MHz to cater for
the current clearance, or just 800 MHz to cater to the last one? If your
problems are due to something like 4G ingress, then you might find they
reappear during the next few years as the 700 MHz bang gets used by the
telcos.

I suspect I'll have to get a new filter, but so far as I know, there isn't
an equivalent to the old AT800 handing out 'AT700' free ones. Anyone know
if there is?

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics https://www.st-andrews.ac.uk/~www_pa...o/electron.htm
biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #57  
Old August 27th 19, 10:36 PM posted to uk.tech.digital-tv
Stephen[_10_]
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Posts: 38
Default UHF home distribution and witchcraft

On 24/08/2019 16:23, Bob Latham wrote:
In article ,
charles wrote:
In article ,
Bob Latham wrote:
In article ,
Jim Lesurf wrote:
In article , charles
wrote:


It used to be the case that amplifiers needed to be derated
if handling more than 4 channels. It does sound as though
there's a spurious signal somehere close to ch 39/40. So,
try increasing the value of that attenuator.


I've been assuming the meter Bob has is 'better' for his
purposes than using an SDR dongle because it is designed for
DVB-T/T2 work and can analyse the modulation, etc. However if
the problem is caused by something like an 'out of band'
oscillation or interference blowing the hat off the TV, would
his meter let him discover this? I recall once using an RS
board as a UHF preamp which almost always oscillated at just
above a GHz. i.e. above the TV UHF band, but if large enough
might still bugger about a modern TV's SDR tuner.


Since the FUNCubeProPlus can go up to about 2GHz it can show
such things. Can Bob's meter? Can the cheap SDR dongles?


okay, please try not to laugh too loud.


Here is a photo of what my cheapo analyser shows for the signal
entering the distribution amp.


http://www.mightyoak.org.uk/analyser1.jpg


left to right..
C22 and C25 are my T1 modulators
C39-C40 C42-C43 C45-C46 C48 C55-C56 are Sutton Coldfield
C60 and C61 are the unused analogue output from a sky box.
Note the chosen channel is C61 and C60 looks like a sideband.


There's a very high noise floor in the centre (39-56)


It is high at 41,44,47 this is The Wrekin transmitter 90 deg away
from Sutton. Wrekin does not have any muxes on the same channels as
Sutton but I've not found a way to filter between wanted channels
without damaging them so I'm stuck with those. I've said on here many
times that whoever thought of placing Wrekin muxes between Sutton's
should be .... They are low enough that TVs ignore them though.

Below 39, is mostly Brierley Hill but at least you can filter when
things are further away.

Sutton 39,40,42,43,45,46,48,55,56
Brierley Hill (very, very strong) 29,31,32,33,34,35,37
Wrekin 23,26,30,41,44,47

BH is about 1.5 miles away and visible. Although vertically polarised
and 45deg off beam I still get vastly more signal from BH than
Sutton. I'm sure many local people think they get their TV from
Wrekin or Sutton but I bet very few do since BH moved frequency.


Cheers,

Bob.

Hi Bob,

I think Google groups is missing some messages so I ended up firing my
Virgin media newgroup server access via Thunderbird tonight

Have you wondered about combining the six muxes from Brierley HIll with
Sutton Coldfield's Muxes 7 & 8 at ch 55 & 56?

BH is after all a relay for Sutton Coldfield's PSB1-3 and Com 4-6....

IIRC, that Avant 3 can take two aerial inputs?

S.
  #58  
Old August 27th 19, 10:52 PM posted to uk.tech.digital-tv
Stephen[_10_]
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Posts: 38
Default UHF home distribution and witchcraft

On 25/08/2019 10:49, Bob Latham wrote:
In article ,
charles wrote:

Giving what level input?


Just done this again to get that info. This is the fully processed
aerial signal just after the 24dB attenuator being connected directly
into the input of the distribution amp.

C39
Level 68dBuV
CN 31.5dB
BER 99%
MER 99%


C40
Level 69dBuV
CN 28dB
BER 99%
MER 99%

Obviously 9dB lower with the extra attenuator added.

I've not got the experience to know if those figures are good, bad or
indifferent to be honest.


Bob.


What is the gain of the distribution amp?

the signal going in is clearly above 60dBuV so with the amplifier gain
added on, i am wondering if the wall plate signals are even higher?

 




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