On the subject of TV engineers.

  LastChip 16:03 03 Feb 2008

Please, can anyone answer this for me?

At home, I have an analogue TV distribution amplifier capable of supplying eight TV's. (No, I don't have eight!). But when we are all forced to switch over to digital, keeping in mind digital signals are somewhat different, will this amplifier be useless?

I appreciate multi-band amplifiers are now available, but are these special, or just a newly named replacement for what I already have? It's about 5-6 years old.

  Totally-braindead 16:10 03 Feb 2008

I must admit I've never even considered this. I have a booster on my TV and it boosts my signal both digital and analogue and I assumed that it would continue to do so.

You have me wondering if this is not the case.

  oresome 16:43 03 Feb 2008

I would expect the amplifier to be OK. It's possible your digital channels will deviate outside the existing analogue band, but the chances are that the amplifier is wideband and will accommodate this.

  crosstrainer 16:46 03 Feb 2008

The booster has to be DVB ready. Bought one the other day in Tesco for 8.97, works a treat...(just 2 lcd tv's but 3 digi boxes) The booster should have a DVB logo on it.

  jz 21:38 04 Feb 2008

It will probably be OK. Now for the technical bit...

Since the days of analogue TV, TV aerials and equipment has come in three main "groups". The UHF TV spectrum is divided up into three groups called A, B and C/D. The reason for this is that it makes aerials more efficient, since they only need to operate over a narrower range of frequencies. Before digital came along, virtually all analogue transmitters transmitted signals in one group. When digital appeared, it wasn't always possible to fit all of the digital channels into the same group as the analogue channels, although where possible, they were. The result was that some areas needed a "wideband" aerial that covered all three groups. That sounds good, but unfortunately the aerial performance goes down as its bandwidth is widened.

It is easier to design distribution amplifiers which are wideband - although some are groups, it is fairly rare to find them.

  lotvic 22:22 04 Feb 2008

Errr... thank you for that, but the only bit I really understand is "It will probably be OK"

  LastChip 23:13 04 Feb 2008

Thank you for that.

I do have a VERY basic knowledge of electronics and understand the concept as you explained it.

After I wrote the initial title piece, I realised that, yes, it does work, but I wonder just how efficient it is.

Recently, I bought a new flat panel TV that has built in Freeview.

Now to explain further, my area (London signal) has not yet been converted and we are right on the fringes anyway. It's a cross between London or Anglia, but the family prefers the London schedules. It is a notoriously weak signal area (channel five is lousy) and currently, even the strongest signals on Freeview are around the 48% mark. Many channels are simply not available. I appreciate that should improve on switch over. But I did wonder if a dedicated digital amplifier would improve things as they stand at present and more to the point, will analogue still be distributed through a new amplifier at it's present strength?

  jz 19:46 05 Feb 2008


I think the term "digital amplifier" is marketing hype. If it amplifies analogue, it will amplify digital too.

An aerial amplifier does improve reception when the signal is weak. It's best to put it close to the aerial, so that the length of cable between the aerial and amplifier is kept short. If you put it at the far end of the cable, near your TV set, the signal is weaker here due to cable loss, so the improvement isn't as great. Some aerial amplifiers have a separate mains power supply box that you fit indoors near your TV set which sends power up the aerial cable to the aerial amplifier which can then be in a remote location, near the aerial - these are the best ones, but tend to be more expensive.

"will analogue still be distributed through a new amplifier at it's present strength?" not at its present strength - it will be boosted too, and the analogue picture will be improved as a result. The amplifier treats analogue and digital signals equally - it cannot distinguish between them.

The digital signal itself is actually looks very analogue - it's doesn't look anything like 1's and 0's (two separate levels). If you were to look at it on an oscilloscope (which displays voltage variations against time) it doesn't look digital at all, it looks like noise in fact. But buried deep within it, the digits are there, and your digital TV set converts the signal to the 1's and 0's. I hope that wasn't too technical...

  LastChip 20:39 05 Feb 2008

No, not too technical at all. I've played with an oscilloscope, analogue multi-meters and so on in the past, so do have a passing knowledge.

Many thanks for the reply. I think eventually, I'll go for a new amplifier I've seen that incorporates a voltage supply for a mast-top amp. Hopefully that will give me the best of both worlds; at least as far as best can be ;-)

I'll tick this as resolved, as jz's replies have really answered the question adequately, but if anyone else wants to chime in, please feel free.

  oresome 20:46 05 Feb 2008

Further to jz's comprehensive reply, another point to bear in mind is that the analogue signal is usually much greater in strength than the digital signal and both are present at the amplifier input.

It's easy to overload the amplifier with the analogue signal. The effects will be obvious on an analogue picture*, but if you only watch digital, the overload may not be so obvious**.

* Buzzing sound and picture behind picture.

** Increased bit errors causing picture freezing and sound sync problems much like other digital reception problems manifest themselves.

These overload problems are more likely where the amplifier is fitted, not because the signal is weak, but because there are multiple TV's to feed and you wish to overcome the loss from splitting the signal several ways.

  LastChip 21:49 05 Feb 2008

I'll keep that in mind, though I think the problem I'm experiencing is due to being in a "fringe" area.

As I said earlier in the thread, but perhaps didn't make as clear as I could, channel five has been very poor from day one, even before digital signals were broadcast and has not improved with time. So I think it's an overall signal strength weakness that is at the root of the problem.

For example, if I disconnect the input to the distribution amplifier and use a coupler to connect directly to the main TV cable (ie. straight from the aerial to TV) the picture is appalling.

The amplifier sits in my loft and I suppose the cable run from the top of the mast to the amplifier is about 10M, so it is likely, a mast-head amplifier would improve the strength of the signal to the distribution amplifier.

Whether the combined effect of both amplifiers would be too much, remains to be seen I suppose.

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