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UHF home distribution and witchcraft



 
 
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  #1  
Old August 22nd 19, 04:31 PM posted to uk.tech.digital-tv
Bob Latham
external usenet poster
 
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 5, 2019.

Logic and the breaking down of problems, fault finding etc. and
writing code has been the one thing in my life where even I, the
pessimist and self critic realised I was pretty good compared to
others. That is until I start looking at issues in a UHF distribution
system. It is as though the logic of how to break down a fault just
vanishes and we end up with witchcraft.

I have two faults at the moment on my system at home the core of
which I suppose is an SLX8B distribution amp that also returns remote
control signals and provides power for all the magic eyes.

The signal feeding it has 11 muxes, 9 from Sutton and two of my own
from digital modulators. At the input to this amp everything is
perfect according to my most critical TV and my cheapo
meter/analyser. Specifically the MER and BER are 99% and rock solid
stable. I've also been careful with the signal levels where Tvs tell
me they're 95% signal which seem sensible to me. the levels have been
adjusted on a Televes Avant 3. The analyser says the filter has done
a good job and unwanted signals are at least 28dB lower than the
wanted.

Things change after the amp though. With only a test TV or meter
plugged into one of the outputs and the others disconnected there is
a problem with C40. This is the main T2 mux from Sutton. TVs report
wandering signal quality rapidly moving and dropping to 75% at times.
My meter shows the MER also wandering but the BER is stable. All the
other muxes are fine. I've tried dropping the input signal level as
I've seen these amps overload in the past but no effect.

What witchcraft is this? How can an amplifier be apparently faulty
for one frequency? Bare in mind that COM7/8 also T2 are both 100%
with a similar signal level.

Is the amp faulty, something tells me not, so is it a design fault?
Should I get a replacement the same or a different manufacturer? I
once tried a labgear amp but found the magic eyes wouldn't work with
that even though it stated on the box they should.

Any suggestions?

More witchcraft with the kitchen TV. This claims the quality of C39
(T1 mux on sutton) is appalling, wandering up and down as low as 20%.
My meter shows the signal BER and MER to be the same as at the
amplifier output ie. 99% and stable for both MER and BER. Okay I hear
you say, it must be a poor connection on the TV. I can assure you it
is not. I've unplugged the cable from the tight fit on the back of
the TV and plugged it into the meter/analyser and then waved the
thing around like a loon in order to provoke a poor connection. But
no, the signal remains absolutely fine and still the TV says it is
rubbish. Move the TV to the input of the amplifier and C39 is perfect
with the same connection cable. Grrrr!

For me now logic has failed. Should I get a priest or a gypsy to
assist? :-)

Any advice most welcome.


Cheers,

Bob.

--
Bob Latham
Stourbridge, West Midlands
  #2  
Old August 22nd 19, 06:14 PM posted to uk.tech.digital-tv
charles[_2_]
external usenet poster
 
Posts: 936
Default UHF home distribution and witchcraft

In article ,
Bob Latham wrote:
Logic and the breaking down of problems, fault finding etc. and
writing code has been the one thing in my life where even I, the
pessimist and self critic realised I was pretty good compared to
others. That is until I start looking at issues in a UHF distribution
system. It is as though the logic of how to break down a fault just
vanishes and we end up with witchcraft.


I have two faults at the moment on my system at home the core of
which I suppose is an SLX8B distribution amp that also returns remote
control signals and provides power for all the magic eyes.


The signal feeding it has 11 muxes, 9 from Sutton and two of my own
from digital modulators. At the input to this amp everything is
perfect according to my most critical TV and my cheapo
meter/analyser. Specifically the MER and BER are 99% and rock solid
stable. I've also been careful with the signal levels where Tvs tell
me they're 95% signal which seem sensible to me. the levels have been
adjusted on a Televes Avant 3. The analyser says the filter has done
a good job and unwanted signals are at least 28dB lower than the
wanted.


Things change after the amp though. With only a test TV or meter
plugged into one of the outputs and the others disconnected there is
a problem with C40. This is the main T2 mux from Sutton. TVs report
wandering signal quality rapidly moving and dropping to 75% at times.
My meter shows the MER also wandering but the BER is stable. All the
other muxes are fine. I've tried dropping the input signal level as
I've seen these amps overload in the past but no effect.


What witchcraft is this? How can an amplifier be apparently faulty
for one frequency? Bare in mind that COM7/8 also T2 are both 100%
with a similar signal level.


Is the amp faulty, something tells me not, so is it a design fault?
Should I get a replacement the same or a different manufacturer? I
once tried a labgear amp but found the magic eyes wouldn't work with
that even though it stated on the box they should.


Any suggestions?


More witchcraft with the kitchen TV. This claims the quality of C39
(T1 mux on sutton) is appalling, wandering up and down as low as 20%.
My meter shows the signal BER and MER to be the same as at the
amplifier output ie. 99% and stable for both MER and BER. Okay I hear
you say, it must be a poor connection on the TV. I can assure you it
is not. I've unplugged the cable from the tight fit on the back of
the TV and plugged it into the meter/analyser and then waved the
thing around like a loon in order to provoke a poor connection. But
no, the signal remains absolutely fine and still the TV says it is
rubbish. Move the TV to the input of the amplifier and C39 is perfect
with the same connection cable. Grrrr!


For me now logic has failed. Should I get a priest or a gypsy to
assist? :-)


Any advice most welcome.


The first thing to try would be to remove the signals coming from your own
modulator and just try Sutton on its own. I'd look very closely at ten
outputb of your modulators to see if they are crating a spurious signal on,
or close to, Ch 40.
Charles

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
  #3  
Old August 22nd 19, 07:27 PM posted to uk.tech.digital-tv
Bob Latham
external usenet poster
 
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 5, 2019.

In article ,
charles wrote:

The first thing to try would be to remove the signals coming from
your own modulator and just try Sutton on its own. I'd look very
closely at ten outputb of your modulators to see if they are
crating a spurious signal on, or close to, Ch 40. Charles


Thanks for the suggestion.

I had done this a few days ago prior to finding another fault with a
poor connecting lead. I think due to that I'd mentally ruled it out
as the cause even though I was looking for a different issue last
time I removed it, that was a mistake.

My modulators are on C22 and C25. They combine and then pass through
a 21-30 passband filter for exactly the reason your advice suggests.
There is also a simple filter 21-34 in the combiner filter. The
aerial side of the combiner is 38-65.

Just unplugged the modulators from the filter combiner.
Disappointingly this had no effect on either fault.

Thanks again.

More than happy to try something else if anyone can suggest
something. Does anyone think the distribution amp is dodgy?

Cheers,

Bob.

--
Bob Latham
Stourbridge, West Midlands
  #4  
Old August 22nd 19, 08:42 PM posted to uk.tech.digital-tv
Brian Gaff
external usenet poster
 
Posts: 7,824
Default UHF home distribution and witchcraft

Pick up on the downlead seems to be the most likely culprit on the e kitchen
one.
I wonder could you inadvertently have a piece of coax exactly the right
length to attenuate chh 40? Interesting that the two issues are on adjacent
channels too.

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.!
"Bob Latham" wrote in message
...
Logic and the breaking down of problems, fault finding etc. and
writing code has been the one thing in my life where even I, the
pessimist and self critic realised I was pretty good compared to
others. That is until I start looking at issues in a UHF distribution
system. It is as though the logic of how to break down a fault just
vanishes and we end up with witchcraft.

I have two faults at the moment on my system at home the core of
which I suppose is an SLX8B distribution amp that also returns remote
control signals and provides power for all the magic eyes.

The signal feeding it has 11 muxes, 9 from Sutton and two of my own
from digital modulators. At the input to this amp everything is
perfect according to my most critical TV and my cheapo
meter/analyser. Specifically the MER and BER are 99% and rock solid
stable. I've also been careful with the signal levels where Tvs tell
me they're 95% signal which seem sensible to me. the levels have been
adjusted on a Televes Avant 3. The analyser says the filter has done
a good job and unwanted signals are at least 28dB lower than the
wanted.

Things change after the amp though. With only a test TV or meter
plugged into one of the outputs and the others disconnected there is
a problem with C40. This is the main T2 mux from Sutton. TVs report
wandering signal quality rapidly moving and dropping to 75% at times.
My meter shows the MER also wandering but the BER is stable. All the
other muxes are fine. I've tried dropping the input signal level as
I've seen these amps overload in the past but no effect.

What witchcraft is this? How can an amplifier be apparently faulty
for one frequency? Bare in mind that COM7/8 also T2 are both 100%
with a similar signal level.

Is the amp faulty, something tells me not, so is it a design fault?
Should I get a replacement the same or a different manufacturer? I
once tried a labgear amp but found the magic eyes wouldn't work with
that even though it stated on the box they should.

Any suggestions?

More witchcraft with the kitchen TV. This claims the quality of C39
(T1 mux on sutton) is appalling, wandering up and down as low as 20%.
My meter shows the signal BER and MER to be the same as at the
amplifier output ie. 99% and stable for both MER and BER. Okay I hear
you say, it must be a poor connection on the TV. I can assure you it
is not. I've unplugged the cable from the tight fit on the back of
the TV and plugged it into the meter/analyser and then waved the
thing around like a loon in order to provoke a poor connection. But
no, the signal remains absolutely fine and still the TV says it is
rubbish. Move the TV to the input of the amplifier and C39 is perfect
with the same connection cable. Grrrr!

For me now logic has failed. Should I get a priest or a gypsy to
assist? :-)

Any advice most welcome.


Cheers,

Bob.

--
Bob Latham
Stourbridge, West Midlands



  #5  
Old August 22nd 19, 08:48 PM posted to uk.tech.digital-tv
Brian Gaff
external usenet poster
 
Posts: 7,824
Default UHF home distribution and witchcraft

Well, I guess the only way to find out is swap it out. I don't see how that
can cause the issue with the kitchen one though, unless its the position of
the cable being moved and the cable is picking up crap in one case. I do
remember back in the analogue days being surprised that a connection lead
just 5 inches longer than one that misbehaved worked flawlessly, when there
was no discernable difference other than length.
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.!
"Bob Latham" wrote in message
...
In article ,
charles wrote:

The first thing to try would be to remove the signals coming from
your own modulator and just try Sutton on its own. I'd look very
closely at ten outputb of your modulators to see if they are
crating a spurious signal on, or close to, Ch 40. Charles


Thanks for the suggestion.

I had done this a few days ago prior to finding another fault with a
poor connecting lead. I think due to that I'd mentally ruled it out
as the cause even though I was looking for a different issue last
time I removed it, that was a mistake.

My modulators are on C22 and C25. They combine and then pass through
a 21-30 passband filter for exactly the reason your advice suggests.
There is also a simple filter 21-34 in the combiner filter. The
aerial side of the combiner is 38-65.

Just unplugged the modulators from the filter combiner.
Disappointingly this had no effect on either fault.

Thanks again.

More than happy to try something else if anyone can suggest
something. Does anyone think the distribution amp is dodgy?

Cheers,

Bob.

--
Bob Latham
Stourbridge, West Midlands



  #6  
Old August 22nd 19, 09:15 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 3,601
Default UHF home distribution and witchcraft

On 22/08/2019 16:31, Bob Latham wrote:

Any suggestions?


Does every channel including the modulator ones go through single
channel pass filters?

Bill
  #7  
Old August 22nd 19, 09:20 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 3,601
Default UHF home distribution and witchcraft

On 22/08/2019 19:27, Bob Latham wrote:

More than happy to try something else if anyone can suggest
something. Does anyone think the distribution amp is dodgy?


Possible. Annoyingly the sort of fault they have doesn't always show up
on an analyser.

Bill
  #8  
Old August 22nd 19, 09:35 PM posted to uk.tech.digital-tv
Indy Jess John
external usenet poster
 
Posts: 1,620
Default UHF home distribution and witchcraft

On 22/08/2019 20:48, Brian Gaff wrote:
I do
remember back in the analogue days being surprised that a connection lead
just 5 inches longer than one that misbehaved worked flawlessly, when there
was no discernable difference other than length.


I saw something like that some years ago. The place where I worked at
the time was putting in a communications network. They had bought the
kit and I was doing the monitoring software; the network when live was
supposed to reroute across a mesh design in the event of a link failure.
I was testing the logic of this.

I set the network up in a spare rack and linked it in the connection
arrangement that would emulate the live configuration. When I first
fired it all up, it said there was a link down. All the "wide area"
connections showed the appropriate working lights, so it had to be the
"local" wiring. There were two supposedly identical connecting leads,
and one worked and the other one didn't. The only difference was the
length - a pin-to-pin check showed that both provided an identical
connection on a DC meter, yet one passed data and the other one didn't.
Disconnecting one end of the "dud" one and cutting 8 inches off before
reconnecting the end and moving the unit it served down a shelf so that
the shorter wire reached, brought it back into life.

I never did find out why 8 inches of wire made such a difference, but it
had to be a capacitance or crosstalk alteration. I wonder if your
kitchen TV is seeing something similar. Try another lead of a different
length?

Jim

  #9  
Old August 22nd 19, 09:40 PM posted to uk.tech.digital-tv
Bob Latham
external usenet poster
 
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 5, 2019.

In article ,
Bill Wright wrote:
On 22/08/2019 16:31, Bob Latham wrote:


Any suggestions?


Does every channel including the modulator ones go through single
channel pass filters?


Bill


Easiest way to answer that please see diagram at:
www.mightyoak.org.uk/diag.jpg

There are only 2 modulators, the one shown on C28 isn't connected.


Thanks

Bob.

--
Bob Latham
Stourbridge, West Midlands
  #10  
Old August 22nd 19, 09:40 PM posted to uk.tech.digital-tv
[email protected]
external usenet poster
 
Posts: 122
Default UHF home distribution and witchcraft

I did have a an issue where a masthead amp started oscillating and trampled over a mux.

On my spectrum analyser it looked like a spike that was about 20 dB above the digital levels. In my case it was at 650 MHz.

Swapping out the masthead cured that issue.

I have had occasions particularly on computers where a certain mux could not be received reliably.

Digging around revealed that the troublesome mux was on a specific frequency that was also used on the computer motherboard.

In this case, it was the motherboard bus frequency of 650MHz wiping out the mux that was being affected. I was on Sandy heath at the time before analogue switch off. The tuner card was an internal version but swapping it to a USB tuner version sorted it.
 




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