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Looks like I managed to find the cause of 4g getting into the Ch 62and Ch 64 modulators....



 
 
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  #1  
Old July 17th 19, 11:10 PM posted to uk.tech.digital-tv
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Default Looks like I managed to find the cause of 4g getting into the Ch 62and Ch 64 modulators....

I have a bank of ten analogue modulators so that all of the CCTV cameras are viewable on all TV sets in the house. All this is combined with Freeview, Freesat, dab and fm.

For sometime I had been plagued with tyre track interference of digital origin on Ch 62 and 64 regular as clockwork every late evening from around 9 pm to 11 pm.

Tonight, I got an opportunity to investigate further.

I always have a spectrum analyser plugged into one of the output ports of the triax multiswitches in the loft.

Sure enough, turning the spectrum analyser showed that there was two 4g mobile phone signals overlaid on the analogue ch62 and ch64 signals.

All of my aerials have 2 off 4g filters on them so I was sure the 4g signals was getting in via a different route.

I noticed that the signal levels of all signals kept fluctuating on the analyser. I traced this to be a bad connection between the crimp on f connector and the outer screen of the ct100 cable at the spectrum analyser's input socket

I carefully dissected the cable and found that the dielectric had split all round the centre conductor at about 10 mm from the f connector so there was just air between the centre wire and screen.

Fitting a new f connector sorted that out and at the same time the 4g signals overlaid on ch62 and Ch64 disappeared. All of the TVs did not show any tyre tracks on ch62 or Ch64.

It appears that the fault on the patch lead between one of the multiswitch outputs and the spec analyser was allowing in 4g signals. This then travelled back up to the multiswitch and then got into all of the other 31 outputs.......

One to chalk up for experience!


  #2  
Old July 18th 19, 01:42 AM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 3,601
Default Looks like I managed to find the cause of 4g getting into the Ch62 and Ch 64 modulators....

On 17/07/2019 23:10, wrote:
I have a bank of ten analogue modulators so that all of the CCTV cameras are viewable on all TV sets in the house. All this is combined with Freeview, Freesat, dab and fm.

For sometime I had been plagued with tyre track interference of digital origin on Ch 62 and 64 regular as clockwork every late evening from around 9 pm to 11 pm.

Tonight, I got an opportunity to investigate further.

I always have a spectrum analyser plugged into one of the output ports of the triax multiswitches in the loft.

Sure enough, turning the spectrum analyser showed that there was two 4g mobile phone signals overlaid on the analogue ch62 and ch64 signals.

All of my aerials have 2 off 4g filters on them so I was sure the 4g signals was getting in via a different route.

I noticed that the signal levels of all signals kept fluctuating on the analyser. I traced this to be a bad connection between the crimp on f connector and the outer screen of the ct100 cable at the spectrum analyser's input socket

I carefully dissected the cable and found that the dielectric had split all round the centre conductor at about 10 mm from the f connector so there was just air between the centre wire and screen.

Fitting a new f connector sorted that out and at the same time the 4g signals overlaid on ch62 and Ch64 disappeared. All of the TVs did not show any tyre tracks on ch62 or Ch64.

It appears that the fault on the patch lead between one of the multiswitch outputs and the spec analyser was allowing in 4g signals. This then travelled back up to the multiswitch and then got into all of the other 31 outputs.......

One to chalk up for experience!



Always check the screen! I've had some orrible frights that were
resolved by checking the screen.

Bill
  #3  
Old July 18th 19, 08:53 AM posted to uk.tech.digital-tv
Brian Gaff
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Default Looks like I managed to find the cause of 4g getting into the Ch 62 and Ch 64 modulators....

So is this crap cable or some kind of mechanical problem at some point in
the cables history. If I had a quid for every probe that went intermittent
on HP gear I used to use at the TV factory back in the day, I'd be rich.
They may have made great test gear but their cable assembly was crap.
Brian

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...
I have a bank of ten analogue modulators so that all of the CCTV cameras
are viewable on all TV sets in the house. All this is combined with
Freeview, Freesat, dab and fm.

For sometime I had been plagued with tyre track interference of digital
origin on Ch 62 and 64 regular as clockwork every late evening from around
9 pm to 11 pm.

Tonight, I got an opportunity to investigate further.

I always have a spectrum analyser plugged into one of the output ports of
the triax multiswitches in the loft.

Sure enough, turning the spectrum analyser showed that there was two 4g
mobile phone signals overlaid on the analogue ch62 and ch64 signals.

All of my aerials have 2 off 4g filters on them so I was sure the 4g
signals was getting in via a different route.

I noticed that the signal levels of all signals kept fluctuating on the
analyser. I traced this to be a bad connection between the crimp on f
connector and the outer screen of the ct100 cable at the spectrum
analyser's input socket

I carefully dissected the cable and found that the dielectric had split
all round the centre conductor at about 10 mm from the f connector so
there was just air between the centre wire and screen.

Fitting a new f connector sorted that out and at the same time the 4g
signals overlaid on ch62 and Ch64 disappeared. All of the TVs did not show
any tyre tracks on ch62 or Ch64.

It appears that the fault on the patch lead between one of the multiswitch
outputs and the spec analyser was allowing in 4g signals. This then
travelled back up to the multiswitch and then got into all of the other 31
outputs.......

One to chalk up for experience!




  #4  
Old July 18th 19, 03:21 PM posted to uk.tech.digital-tv
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Posts: 122
Default Looks like I managed to find the cause of 4g getting into the Ch62 and Ch 64 modulators....

It's funny you mention that.....

I was raised to use copper on copper fully screened CT100 grade cables...

I always use screw on F connectors.

I live in an area served by virgin media.

One day they sent me a cable modem, cable tv set top box, a splitter and three lengths of white coax which had crimped on f connectors at both ends.

I only installed the cable modem so I had some unused VM patch leads.

One of them ended up connecting my spectrum analyser to one of the output sockets of the multiswitches.

It was this cable I dissected last night. To my extreme surprise I found that it was aluminium mylar foil on steel braid!

It seems VM use cheap coax for their cable system!

I will replace this with copper on copper ct100 grade cable and the VM white string can go in the bin!
  #5  
Old July 19th 19, 05:35 PM posted to uk.tech.digital-tv
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Posts: 1,282
Default Looks like I managed to find the cause of 4g getting into the Ch 62 and Ch 64 modulators....

On Wed, 17 Jul 2019 15:10:46 -0700 (PDT), wrote:

I have a bank of ten analogue modulators so that all of the CCTV cameras are viewable on all TV sets in the house. All this is combined with Freeview, Freesat, dab and fm.

For sometime I had been plagued with tyre track interference of digital origin on Ch 62 and 64 regular as clockwork every late evening from around 9 pm to 11 pm.

Tonight, I got an opportunity to investigate further.

I always have a spectrum analyser plugged into one of the output ports of the triax multiswitches in the loft.

Sure enough, turning the spectrum analyser showed that there was two 4g mobile phone signals overlaid on the analogue ch62 and ch64 signals.

All of my aerials have 2 off 4g filters on them so I was sure the 4g signals was getting in via a different route.

I noticed that the signal levels of all signals kept fluctuating on the analyser. I traced this to be a bad connection between the crimp on f connector and the outer screen of the ct100 cable at the spectrum analyser's input socket

I carefully dissected the cable and found that the dielectric had split all round the centre conductor at about 10 mm from the f connector so there was just air between the centre wire and screen.

Fitting a new f connector sorted that out and at the same time the 4g signals overlaid on ch62 and Ch64 disappeared. All of the TVs did not show any tyre tracks on ch62 or Ch64.

It appears that the fault on the patch lead between one of the multiswitch outputs and the spec analyser was allowing in 4g signals. This then travelled back up to the multiswitch and then got into all of the other 31 outputs.......

One to chalk up for experience!


But why was the interference daily at the same times?
  #6  
Old July 20th 19, 01:40 AM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 3,601
Default Looks like I managed to find the cause of 4g getting into the Ch62 and Ch 64 modulators....

On 19/07/2019 17:35, lid wrote:

But why was the interference daily at the same times?


Pragmatic approach to this sort of thing is to find a fix and forget the
whys and wherefores.

Bill
  #7  
Old July 20th 19, 08:13 AM posted to uk.tech.digital-tv
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Posts: 122
Default Looks like I managed to find the cause of 4g getting into the Ch62 and Ch 64 modulators....

That puzzled me too. I can only assume that someone nearby was facetiming or whatsapping or Facebooking or instagramming from a house near me regular as clockwork before going to bed?
  #8  
Old July 20th 19, 12:16 PM posted to uk.tech.digital-tv
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Posts: 122
Default Looks like I managed to find the cause of 4g getting into the Ch62 and Ch 64 modulators....

I was surprised also at the ease that 4g signal can get into a downlead, travel all the way back to the first multiswitch, get back out onto the other 15 outputs of that multiswitch.

On top of that, that 4g signal was able to travel upstream to the triax tms55 trunk splitter, come back out on the other trunk output and then into the second multiswitch and then out on all 16 outputs of that 2nd multiswitch....
 




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