Signal strength and quality

[stuartR1963]

Hi, apologies if this is a daft question but I am trying to understand how signal strength and quality go hand in hand? My understanding is the bare minimum signal strength to make a tv work is 45dbuv. Let's say the signal strength was 45dbuv bare minimum and the signal quality was good, am I correct in thinking the tv will work perfectly well without pixelation ect, but just some channels will be missing because the strength is not high enough to pick up every single channel from the transmitted frequencies, in other words all tv channels the tv has managed to store will work perfectly well because the signal quality is good but because the strength is only minimal not all channels may be available such as itv3 for example?
Thanks

 

[stuartR1963]

Obviously my above example is taking into account using the correct aerial for the appropriate transmitter and the tv has been manually tuned. I know auto tuning can sometimes pick up rubbish hence manual tuning.
Thanks

 

[Lucid]

Painting with a very broad brush, Quality is a measure of the difference between all the background noise and the signal level itself. Strength is simply a measure of how large the signal is, whether that's clean or noisy.


Let's take your 45dB minimum strength as a starting point. It's a guideline minimum to get all the stations, strong or weak. It is possible to get perfectly decent reception at less than 45dB, but it doesn't leave much wiggle room if say the atmospheric conditions change or something else temporary causes the signal level to drop.

A signal level of 55dB at the set's aerial socket is a sensible target point. It gives a reasonable amount safety margin for fluctuations, and it isn't going to oversaturate a tuner.

65dB is the recommended upper limit, but there's still another 5dB or so headroom for most TVs.

All the above relies on there being a big enough difference between the background noise and the carrier signal. It's perfectly possible to have 65dB of strength, but a lousy carrier to noise ratio (CNR) which means pixelated reception. This sort of thing happens when there's a problem say with the aerial alignment resulting in a poor CNR, and then the owner adds an amplifier at the back of the TV to 'boost' the signal. Electronic amplification adds its own noise, and so makes the CNR worse, while making the total signal (including the old background noise) louder.

Passive splitters reduce the signal Strength but add no noise.

Digital signal levels is really quite a big topic. We measure CNR and the Bit Error Rate (BER), but there are different guidlines for some of this data depending on the signal modulation such as 64 QAM and 256 QAM. It's easy to get lost down the rabbit hole.

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[ericmark]

We were always told, you can amplify rubbish and get a good signal strength but the result is still rubbish.

 

[stuartR1963]

Sorry for late reply, so the goal when setting up an aerial system is to obviously use good quality double screen coax, the correct aerial for the correct transmitter, get the signal strength for all frequencies between 55 and 65db and then prioritize the signal quality? Does that sound correct.
Thanks

 

[ericmark]

Main idea if your going to use an amplifier then fit amplifier close to the aerial so good signal is amplified not a poor one. Also use an aerial designed for the frequency being received. Good quality coax is also good but that depends on distance. Not all TV's and set top boxes are equal, my Sky boxes were deaf compared with my free to air boxes, and my TV direct only receives some stations, but where I live freeview is rubbish, it needs satellite.

However I still use aerials for other things and the same applies, try and reduce loses.

 

[Lucid]

Sorry for late reply, so the goal when setting up an aerial system is to obviously use good quality double screen coax, the correct aerial for the correct transmitter, get the signal strength for all frequencies between 55 and 65db and then prioritize the signal quality? Does that sound correct.
Thanks

Yeah, that's pretty-much it.

Signal Quality comes from one place: the aerial. Everything we do with that signal after it leaves the aerial has an impact on Strength and/or Quality.