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UHF home distribution and witchcraft



 
 
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  #21  
Old August 23rd 19, 05:22 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Default UHF home distribution and witchcraft

No system should include a 24dB attenuator. A good general rule is have
the minimum of amplification on every signal path. Large value
attenuators go against that.

However the first thing to do when looking for a simple dirty fix is to
swap out the amplifier at the end of the system.

Bill
  #22  
Old August 23rd 19, 06:41 PM posted to uk.tech.digital-tv
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Default UHF home distribution and witchcraft

I understand the reason for the 24 dB attenuator as he has an Avant 3.

My Avant 5 outputs in the range of 92 to 111 dBuV.

Although it then goes through two multiswitches resulting in a through path split of 15 dB from input to all of the 32 outputs.

So that 92 to 111dBuV becomes 77 to 96 dBuV.

With the DTT signals supposed to be 45 to 60 dBuV at the wall plates, attenuation of 17dB to 51dB is going to be required!
  #23  
Old August 23rd 19, 07:19 PM posted to uk.tech.digital-tv
charles[_2_]
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Default UHF home distribution and witchcraft

In article ,
wrote:
I understand the reason for the 24 dB attenuator as he has an Avant 3.


My Avant 5 outputs in the range of 92 to 111 dBuV.


Although it then goes through two multiswitches resulting in a through
path split of 15 dB from input to all of the 32 outputs.


So that 92 to 111dBuV becomes 77 to 96 dBuV.


With the DTT signals supposed to be 45 to 60 dBuV at the wall plates,
attenuation of 17dB to 51dB is going to be required!


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.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
  #24  
Old August 23rd 19, 08:22 PM posted to uk.tech.digital-tv
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Default UHF home distribution and witchcraft

Another possibility is the analogue UHF output of that sky box it is putting out on its rf1 and rf2 sockets clashing or being 1 or 5 or 9 channels away from the affected mux.

I would move the sky's analogue RF out to Ch 69 ( many sky boxes can do this even though the TVs can only go up to 68.)
  #26  
Old August 23rd 19, 11:19 PM posted to uk.tech.digital-tv
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Default UHF home distribution and witchcraft

Ok...

I got the Avant 5's for far cheaper than a set of Taylor bros filters would have cost me.

Additionally the Avant 5 is frequency agile so when DSO happened, when 4g clearance happened, and in the midst of the current 5g clearance, I can reprogram the Avant 5 instead of replacing the Taylor bros filter clusters as there is only so far you can retune them to.

There was no way to crank the output amplifier down on the Avant or even bypass it completely to use it in filter mode only.

Not only that, the Avant 5 will not process the input signals and autolevel the output signals unless they are already 60 dBuV or higher .... (!) So all my log periodics have masthead amplifiers on them.

If anyone knows of any hacks on the televes Avant 5's I am all ears so I can remove the 27dB attenuator I have between the Avant 5's and the triax multiswitches....
  #27  
Old August 24th 19, 09:40 AM posted to uk.tech.digital-tv
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Default UHF home distribution and witchcraft

As promised, a revised distribution diagram!

https://www.flickr.com/photos/183769...posted-public/

Some comments...

1. I recall you were trying to prevent Brierley Hill from entering your TV system so I understand why you have the two band pass filters before and after the labgear amp, and also the two notch filters for ch 37 and ch 47.

2. I note the labgear is a mains powered unit. My preference would be a masthead amplifier powered directly from the Televes 3. That will remove the mains circuitry away from the signal path....

3. Am I right in assuming that the Labgear has 4G filtering hence the the ch59 filter or is this a 4G filter you added? If the latter, this is better put in BEFORE the amplifier.

4. The DC block? You should be able to turn off DC powering in the Televes 3 which then means you can remove the DC block. If you do get a new masthead amp, you can power this directly from the Televes 3 (Check the voltage) but that band pass filter will need to pass the DC as well.

5. The ch 37 and ch 47 notch filter is better put BEFORE an amplifier rather than after? Have you tried it before the amp?

6. Am I right in assuming that the Televes 3 requires a minimum input signal level before it will set itself up correctly? Or is it a case of your SC signals being weak/marginal? I've no experience of the Televes 3 but lots of experience with Televes 5 units.

7. I know Bill has commented on the 24dB attenuator. I do agree with him but I've never managed to find a domestic grade channel agile filter cluster with signal autolevelling. The Televes units we both have are aimed more at hotels and commercial premises. So you are stuck with the attenuator like me. :-)

8. You will in the new map that immediately after sorting out the SC signals, there is an immediate 3 way split. two of which go to your set top boxes The third output is left "unmolested" and rejoins the network late as possible immediately before the SLX amp.

9. As Bill says, a Star network topology is far better than looping in and looping out. Thus there is no RF looping from one set top box to the other which prevents the adding of electrical noise by their internal modulators to the signal path.

10. After all your set top boxes the digital modulators are then combined to a single output followed by the ch 21 to 30 bandpass filter. In an ideal world, I would use channelised filters and signal autolevelling (like a 2nd Televes 3!) In my case I have 10 CCTV modulators which feeds an AVANT 5. The output of this is them combined with the other Avant 5s which are processing my freeview signals. Then the whole lot goes into my multiswitches.

11. The output of the "unmolested as much as possible" SC signals are then combined with the digital modulator outputs via that filter combiner.

12. This is then combined with the Output of the TVLink+ using a simple DC passing 5MHz to 2300 MHz combiner. This should allow the TV link signals to pass back through to the unit. If you have problems with the remote controls, then you will have to move the combiner to before the TVLink unit and combine with the output of the Sky HD box.

13. Move the UHF output of the Sky HD box to Ch 69 so that's its well away from all the other wanted signals, In your system, your highest frequency is ch 56 Mux 8 and your lowest channel is ch 22. SO CH 69 is going to be 13 channels away from ch 56.

No doubt Bill can suggest further ideas & thoughts to what I've written.

Let us know how you get on!

S.
  #28  
Old August 24th 19, 10:46 AM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
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Default UHF home distribution and witchcraft

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?

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

  #30  
Old August 24th 19, 12:20 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 3,601
Default UHF home distribution and witchcraft

On 24/08/2019 09:40, wrote:
As promised, a revised distribution diagram!

https://www.flickr.com/photos/183769...posted-public/

Some comments...

1. I recall you were trying to prevent Brierley Hill from entering your TV system so I understand why you have the two band pass filters before and after the labgear amp, and also the two notch filters for ch 37 and ch 47.

2. I note the labgear is a mains powered unit. My preference would be a masthead amplifier powered directly from the Televes 3. That will remove the mains circuitry away from the signal path....

3. Am I right in assuming that the Labgear has 4G filtering hence the the ch59 filter or is this a 4G filter you added? If the latter, this is better put in BEFORE the amplifier.

4. The DC block? You should be able to turn off DC powering in the Televes 3 which then means you can remove the DC block. If you do get a new masthead amp, you can power this directly from the Televes 3 (Check the voltage) but that band pass filter will need to pass the DC as well.

5. The ch 37 and ch 47 notch filter is better put BEFORE an amplifier rather than after? Have you tried it before the amp?

6. Am I right in assuming that the Televes 3 requires a minimum input signal level before it will set itself up correctly? Or is it a case of your SC signals being weak/marginal? I've no experience of the Televes 3 but lots of experience with Televes 5 units.

7. I know Bill has commented on the 24dB attenuator. I do agree with him but I've never managed to find a domestic grade channel agile filter cluster with signal autolevelling. The Televes units we both have are aimed more at hotels and commercial premises. So you are stuck with the attenuator like me. :-)

8. You will in the new map that immediately after sorting out the SC signals, there is an immediate 3 way split. two of which go to your set top boxes The third output is left "unmolested" and rejoins the network late as possible immediately before the SLX amp.

9. As Bill says, a Star network topology is far better than looping in and looping out. Thus there is no RF looping from one set top box to the other which prevents the adding of electrical noise by their internal modulators to the signal path.

10. After all your set top boxes the digital modulators are then combined to a single output followed by the ch 21 to 30 bandpass filter. In an ideal world, I would use channelised filters and signal autolevelling (like a 2nd Televes 3!) In my case I have 10 CCTV modulators which feeds an AVANT 5. The output of this is them combined with the other Avant 5s which are processing my freeview signals. Then the whole lot goes into my multiswitches.

11. The output of the "unmolested as much as possible" SC signals are then combined with the digital modulator outputs via that filter combiner.

12. This is then combined with the Output of the TVLink+ using a simple DC passing 5MHz to 2300 MHz combiner. This should allow the TV link signals to pass back through to the unit. If you have problems with the remote controls, then you will have to move the combiner to before the TVLink unit and combine with the output of the Sky HD box.

13. Move the UHF output of the Sky HD box to Ch 69 so that's its well away from all the other wanted signals, In your system, your highest frequency is ch 56 Mux 8 and your lowest channel is ch 22. SO CH 69 is going to be 13 channels away from ch 56.

No doubt Bill can suggest further ideas & thoughts to what I've written.

Let us know how you get on!

S.


As a general thought, well, err, I've been called to many a system that
doesn't actually have one obviously identifiable fault. Instead it has
died 'the death of a thousand cuts'. A rethink of actual requirements,
the removal of obsolete equipment,then a complete rejig using as many
existing components as possible, is called for.

"So did you find the fault?"

"Not really..."

Bill
 




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