Analogue distribution of signal from Sky box

[JohnW2]

Hi folks, I wonder if anyone can help me with some thoughts about this ...

I have a many-years old system which distributes signals from my TV aerial and the analogue output of a Sky+ box to half a dozen TVs scattered throughout my (large) house, using coax and a 6-output distribution box (very close to, and fed from, the Sky Box)..

The distributed DTV has always been fine, even for those TVs which have pretty long coax runs from the distribution box. However, the signal from the Sky box has, although 'usable', never been brilliant (varying, usually fairly minor, minor degrees of 'snowstorm'), even on the TV with the shortest cable run. I originally used the Sky box's default Channel of 68, but subsequently changed it to 48 ('just in case') but that altered nothing.

After many years, I've recently tried to improve the situation. Assuming that it was a signal strength issue, the first thing I tried was to add an amplifier. I tried with three different ones which I had to hand, with gains of 7dB, 12dB and 23dB respectively, and in each case tried putting the amplifier in one of three different places:

. (a) between Sky+ box and the distribution box
. (b) at the distribution box end of one of the cables from distribution box to a distant TV
. (c) at the ('remote') TV end of one of the cables from distribution box to a distant TV

Somewhat to my surprise, not only did none of these experiments (with the three amplifiers in three different places) improve the situation but, in all cases, addition of the amplifier actually considerably worsened the situation, in some cases almost to the extent of destroying the signal rom the Sky box.

I may be missing something, or not thinking straight, but I wonder if anyone has any thoughts, suggestions or advice?

Kind Regards, John

 

[Lucid]

Sky's RF out was never the best, but it was (and still is) possible to pick a better RF channel based on avoiding proximity with the other channels within the system.

You might be thinking that the other channels are digital so they can affect an analogue channel, but that wouldn't be correct. Although the Freeview signal is sent in a form to be decoded by the DVB-T/T2 tuner, it still occupies the same channel space as analogue would have. The result of overlapping on one of these is a very snowy picture.

We also have 2G/3G/4G and now 5G encroaching on the upper end of the old RF Ch 21-68 range. Since the 800MHz and more recent 700MHz clearance events the TV band is now between RF Ch21 and 49 which is 698MHz at the upper end. This means that from ch50 (704MHz) up to RF Ch68 (850MHz) could have mobile phone signals at certain frequencies.

Sky RF Out has always responded best at higher frequencies, the equivalent to higher RF channel numbers.

Where I am, RF Ch 68 works pretty well. Your mileage may vary. The trick used to be to try to choose an RF channel at least 3 channel positions away from the nearest digital channel. That was before all the digital channels got squashed down in to a smaller range. Depending where you are and what other transmitters are in your area it might not be possible to pick something within the 21-49 range, so you might be better off working your way down from ch68 to see what works for you. Failing that, you can always make some clear space by installing a 4G/5G filter. LINK

You might also be experiencing some pick-up of more distant transmitters due the the high pressure weather we're having at the moment. This could affect your tuning in the TV band. It may also impact with 4G/5G but I'm not 100% sure on that.

If you get fed up with the analogue RF channel solution then you can switch across to using the clearer DVB-T2 digital tuner, though the hardware itself is a chunk of cash and you do need to make sure all the TVs have the suitable DVB-T2 tuners. LMK if you want to look at that as an option. The box for it is around the £200 mark as a ball park figure.




4G/5G Filter: https://www.tlc-direct.co.uk/Produc...iusTOvcMvLJ5MnlJCKBwSRM3Ennd_78hoC6BIQAvD_BwE

 

[JohnW2]

Sky's RF out was never the best, but it was (and still is) possible to pick a better RF channel based on avoiding proximity with the other channels within the system.

Hi Lucid. Thanks for your interest and for your rapid and detailed reply. Yes, I appreciated the above, which is why I tried changing the RF channel from 68 to 48, but when that made absolutely no difference, I (perhaps inappropriately) somewhat lost interest in changing it further!

You might be thinking that the other channels are digital so they can affect an analogue channel, but that wouldn't be correct. Although the Freeview signal is sent in a form to be decoded by the DVB-T/T2 tuner, it still occupies the same channel space as analogue would have. The result of overlapping on one of these is a very snowy picture.

Fair enough [I presume you mean "... cannot affect an analogue channel..."?]. A 'slightly snowy' picture is what I've been experiencing, so maybe such 'overlapping' is at least part, if not all, of the issue..

We also have 2G/3G/4G and now 5G encroaching on the upper end of the old RF Ch 21-68 range. Since the 800MHz and more recent 700MHz clearance events the TV band is now between RF Ch21 and 49 which is 698MHz at the upper end. This means that from ch50 (704MHz) up to RF Ch68 (850MHz) could have mobile phone signals at certain frequencies.

At least some, if not all, of the amplifiers I tried adding had 3G/4G filters but, as I said, for what it's worth they all made things much worse, not better. The channel 48 I'm currently using is just inside the 'now' TV band you mention, hence presumably away from potential pohone signal issues?

Sky RF Out has always responded best at higher frequencies, the equivalent to higher RF channel numbers.

Thanks. That I didn't know. In fact, I had ('intuitively') rather suspected the opposite!

Where I am, RF Ch 68 works pretty well. Your mileage may vary. The trick used to be to try to choose an RF channel at least 3 channel positions away from the nearest digital channel. That was before all the digital channels got squashed down in to a smaller range. Depending where you are and what other transmitters are in your area it might not be possible to pick something within the 21-49 range, so you might be better off working your way down from ch68 to see what works for you.

Fair enough. If it helps to identify what channels/frequencies I'm dealing with, I'm getting my digital TV from the Oxford repeater, and the signal strength is very good, since my aerial is literally line-of-sight to the transmitter mast.

Failing that, you can always make some clear space by installing a 4G/5G filter. LINK

As above, at least some of the amplifiers I tried 'adding' had 3G/4G filers - but that, of course, was just with channel 48 being used - so maybe a reason to try different channels with an additional amplifier?

You might also be experiencing some pick-up of more distant transmitters due the the high pressure weather we're having at the moment. This could affect your tuning in the TV band. It may also impact with 4G/5G but I'm not 100% sure on that.

Perhaps I wasn't clear, but what I'm experiencing has been essentially the same for years (it's just that I have now, after all those years, decided to see if I can improve things a bit!) - not only just recently.

You've certainly given me some ideas - probably primarily to persist in trying some different channels - but I still find it hard to understand why all the amplifiers I added mad things a lot worse (and no matter where I inserted them in the signal path). The only thing I can think of is that the problem does relate to some sort of 'overlapping' with DTV channels and the main effect of the amplifier was to increase the strength of the DTV signals that were interfering with the analogue one - does that sound credible?

Thanks again.

Kind Regards, John

 

[Lucid]

Fair enough [I presume you mean "... cannot affect an analogue channel..."?]. A 'slightly snowy' picture is what I've been experiencing, so maybe such 'overlapping' is at least part, if not all, of the issue..

Yeah, you're right. It should read cannot. That was a typo. My bad.

At least some, if not all, of the amplifiers I tried adding had 3G/4G filters but, as I said, for what it's worth they all made things much worse, not better. The channel 48 I'm currently using is just inside the 'now' TV band you mention, hence presumably away from potential pohone signal issues?

From what you wrote in the OP, you placed the amplifiers in positions downstream of the RF output from the Sky box. Therefore the benefit of the 4G filtering was in the wrong place. Here's where you said you tried them:

. (a) between Sky+ box and the distribution box [my read: after the Sky box but before the main distribution amp]
. (b) at the distribution box end of one of the cables from distribution box to a distant TV [my read: at one of the outputs of the distribution amp, on the longest cable run/most distant TV]
. (c) at the ('remote') TV end of one of the cables from distribution box to a distant TV [my read: at one TV, just before the signal enters the set]

In order to be of any benefit, the 4G filtering needs to be before the signal gets to the Sky box. If you will, it needs to clear a path ready for the Sky box to add its RF Out contribution. I wouldn't use one of the amps though for this. If you already have strong signal from the Oxford transmitter then all you're doing with an amp is adding noise and reducing the signal to noise ratio (SNR) whilst boosting the overall signal level.

When we had analogue only, approaches a and b might have worked. However, digital is more picky about SNR. Adding amplification when the signal is already strong will reduce the SNR (with a corresponding reduction in the Quality measure of the digital tuning) and you may even oversaturate the tuner.

Any amplification (if needed, and only if needed) should go as close to the aerial as possible. The aim is to give the signal a boost before it encounters the noise and resistance losses from running through cables and various joints and split points. This is one of the reasons why set-back amps (those that amplify just before the signal gets in to the TV) rarely work. In the case of digital TV, the signal has already lost Strength but not Quality. Amplifying at the set back boosts Strength but cripples Quality.

An amplified splitter/distribution amp is a slightly different case. The amplification is there in the main to compensate for splitting X number of ways.

 

[Tricky-Dicky]

Hi, the Oxford transmitter uses channels 47,44,41,37,29,31, info curtesy of ATV aerials

 

[RandomGrinch]

The distributed DTV has always been fine, even for those TVs which have pretty long coax runs from the distribution box. However, the signal from the Sky box has, although 'usable'

I wonder if it might be more convenient looking at 'upgrading' to a DVB-T modulator? - you then wouldn't have to swap inputs for your distributed channel.

If you get fed up with the analogue RF channel solution then you can switch across to using the clearer DVB-T2 digital tuner, though the hardware itself is a chunk of cash

Would I be way off, suggesting one of these?

EDISION HDMI MODULATOR (single DVB-T) Full HD Distribution over Coax

EDISION HDMI MODULATOR single DVB-T only £107, UK stock! Fast UK next working day delivery!

www.world-of-satellite.co.uk

...there also seem to be some very cheap options on Amazon/eBay, but I dare not leave a link!

 

[Lucid]

Would I be way off, suggesting one of these?

EDISION HDMI MODULATOR (single DVB-T) Full HD Distribution over Coax

EDISION HDMI MODULATOR single DVB-T only £107, UK stock! Fast UK next working day delivery!

www.world-of-satellite.co.uk

...there also seem to be some very cheap options on Amazon/eBay, but I dare not leave a link!

Not at all, although I had in mind something like the Triax MOD103T or the Technomate TM-RF since they include a 1-In-to-2-Out HDMI splitter and 9V power for the Sky RF Eyes, so it keeps things quite neat in not having to have additional bits of gear for those extra functions. The auction site has some of these options around the £150-£160 mark.

It's worth looking if the cheaper options pass 9V. If so, then that solves how to get the channel control signal back to the Sky box in the absence of an IR emitter. You'd still need a HDMI splitter though, and it's best to have one that's independently powered via a wall wart-type transformer rather than either pinching power from a TV USB socket (might not have enough juice / could be unpowered if the TV is off) or trying to run it just using the 5V within the HDMI architecture. This wasn't ever designed to run peripherals as well as powering the sink device (TV) HDMI receiver when the set is in standby.

The modulators with an IR emitter will work with Sky Q's main box should that ever be required, but there is a catch. They max out at 1080p. If someone is watching 4K UHD content and one of these was introduced then they'd lose that ability. The boxes won't pass 4K UHD, and even outboard splitters will struggle to support the connection of a mix of 4K and 1080p TVs via HDMI without pulling everything down to 1080p standard. This is not a problem with the Sky-HD boxes, but it might be a consideration should the box ever have to be replaced in-contract and either an old HD box isn't available or Sky insist that it has to be a Q box however unlikely that might be.

 

[RandomGrinch]

Not at all, although I had in mind something like the Triax MOD103T or the Technomate TM-RF since they include a 1-In-to-2-Out HDMI splitter and 9V power for the Sky RF Eyes

Thank you, yes I hadn't considered the IR extender.
It's nice to know that there are such integrated 'off the shelf' solutions.
I hadn't thought about it before, but I guess these units have uses in the hospitality/guest house/pub sectors (...and for those with big houses! )?

 

[JohnW2]

From what you wrote in the OP, you placed the amplifiers in positions downstream of the RF output from the Sky box. Therefore the benefit of the 4G filtering was in the wrong place. Here's where you said you tried them: ... In order to be of any benefit, the 4G filtering needs to be before the signal gets to the Sky box. If you will, it needs to clear a path ready for the Sky box to add its RF Out contribution. I wouldn't use one of the amps though for this. ....
When we had analogue only, approaches a and b might have worked. However, digital is more picky about SNR. Adding amplification when the signal is already strong will reduce the SNR (with a corresponding reduction in the Quality measure of the digital tuning) and you may even oversaturate the tuner. .... Amplifying at the set back boosts Strength but cripples Quality.

Thanks again, and fair enough. I was not, of course, using the amplifiers for 4G filtering - I merely commented that at least some of the amplifiers had such filtering in response to your comment about it. Mind you, had I been 'wanting' the filtering, I would probably have thought (seemingly wrongly) that the interference between 4G and the TV signal would be at the level of the remote TV's tuner, in which case I might have expected a filter downstream of the Sky box to help.

Having said all that, I have no specific reason to think that the problem is anything to do with 4G - and, indeed, I would have thought it fairly unlikely, given that the situation/'problem' is identical with both channels 68 and 48 ?

If you already have strong signal from the Oxford transmitter then all you're doing with an amp is adding noise and reducing the signal to noise ratio (SNR) whilst boosting the overall signal level.

You actually make me wonder. Given that my signal is so strong, then if the problem is due to 'proximity of channels', I wonder if the situation might be helped by inserting an attenuator upstream of the sky box?

From what Trick-Dicky has told me about the Oxford channels, it sounds as if the Channel 48 I'm now using is probably a bit 'close for comfort' (to Oxford's channel 47) but, by the same token, suggests that the original channel 68 I was using is a long way from any Oxford channel

Kind Regards, John

 

[JohnW2]

Hi, the Oxford transmitter uses channels 47,44,41,37,29,31, info curtesy of ATV aerials

Many thanks. That's useful, and saved lazy me having to look

Kind Regards, John

 

[JohnW2]

Thank you, yes I hadn't considered the IR extender. It's nice to know that there are such integrated 'off the shelf' solutions. I hadn't thought about it before, but I guess these units have uses in the hospitality/guest house/pub sectors (...and for those with big houses! )?

'IR extension' is not an issue for me (even with my 'big house' ). Donkey's years ago I installed separate wiring to facilitate 'IR extension' to all the remote locations - which originally had to be done with home-brewed kit, since off-the-shelf systems were then not available (or, at least, not known to me). My only issue is therefore the quality of the distributed RF.

Kind Regards, John

 

[RandomGrinch]

, I wonder if the situation might be helped by inserting an attenuator upstream of the sky box?

Might there be some amplification from the distribution box?
It could be a simple test to bypass it on the worst effected cable run?

 

[JohnW2]

I wonder if it might be more convenient looking at 'upgrading' to a DVB-T modulator? - you then wouldn't have to swap inputs for your distributed channel.

What do you mean by 'swap inputs'?

Would I be way off, suggesting one of these? ...

I've been aware of that option but, having lived with the present situation for years, am hesitant to spend appreciable money to improve things.

Perhaps more to the point, at present at least one (ancient) of the remote TVs would not work with such a modulator

Kind Regards, John

 

[JohnW2]

Might there be some amplification from the distribution box?

There is - about 7dB per channel. However, as has been said, I think that's primarily to compensate for the 6-way split of the signal, and is probably unavoidable.

It could be a simple test to bypass it on the worst effected cable run?

I've been doing so much playing recently that I've somewhat lost track of what I've done and not done (should have kept records, as my Science teachers would have reminded me!!) - but that's so obvious that I imagine I must have tried it! However, given that I can't even remember for sure that I did it, let alone what the result was, I'll try again shortly!

Kind Regards, John

 

[Lucid]

Thanks again, and fair enough. I was not, of course, using the amplifiers for 4G filtering - I merely commented that at least some of the amplifiers had such filtering in response to your comment about it. Mind you, had I been 'wanting' the filtering, I would probably have thought (seemingly wrongly) that the interference between 4G and the TV signal would be at the level of the remote TV's tuner, in which case I might have expected a filter downstream of the Sky box to help.

Having said all that, I have no specific reason to think that the problem is anything to do with 4G - and, indeed, I would have thought it fairly unlikely, given that the situation/'problem' is identical with both channels 68 and 48 ?

Until you 'clear a path' of any potential 4G interference then you won't really know for sure whether ch48 & 68 are as good as it gets or if they're both subject to a bit of interference. Given the cost of a 4G filter such as the one I linked in the previous post, and the fact that it blankets the whole band rather than being selective in frequency as some older filters were, and how easy one is to install, then it seems to me like an obvious step in your quest to see if this can be improved.

You actually make me wonder. Given that my signal is so strong, then if the problem is due to 'proximity of channels', I wonder if the situation might be helped by inserting an attenuator upstream of the sky box?

From what Trick-Dicky has told me about the Oxford channels, it sounds as if the Channel 48 I'm now using is probably a bit 'close for comfort' (to Oxford's channel 47) but, by the same token, suggests that the original channel 68 I was using is a long way from any Oxford channel

Kind Regards, John

Yes, I'd avoid ch48 personally, but I think that' just beating around the bush.

If I was faced with this situation at a customer installation then I'd fit the 4G filter as a first step. If that wasn't available as an option then I'd run down the RF channels from 68 to 50 and not the good / bad / indifferent and choose the best from there.