What Is The Difference Between TV Signal Strength & Quality?

July 11, 2019
by
Tom

What Is The Difference Between TV Signal Strength & Quality?

 

If you have tuned your TV recently and or have wondered into your Sky box menu and have found a signal quality reading that gives measurements of signal quality and strength, and what to know what this means? Read on for all you need to know.

 

Most TV will give separate readings for both signal and quality but others may not, some may give you just a percentage with no separation between the two and others will give no signal information at all. I had a customer that asked me “Is it like volts and amps?”, I said no it’s not, but it’s not necessarily a bad way of looking at it and got me thinking that others may be wondering what the answer to this question is so I thought I would create an article on the difference between signal strength/ quality and upload it to our blog for all you to enjoy.

 

The TV Signal Reader On The TV Should Be A Guide Only 

When I install TV aerials and satellite dishes I use a Promax Ranger meter, if you look online you will see that this is a very sophisticated piece of equipment. It gives me all sorts of measurements on signal strengths, robustness, interference, signal information & information on signal modulations and allows me to look at the signal constellations should I wish, along with a load of of others things. It allows me to see a digital TV picture if I wish(demodulation), but this isn’t necessary if you know how to read the information on the digital TV signal. I appreciate that this may not mean a lot but the point that I’m making is that this is a suitable piece of equipment for assessing how good a TV signal and how reliable the reception will be. The TV that you use to watch the TV is actually not designed for reading signal strength and quality so the readings that it may give you can be very misleading. The picture itself certainly can't be trusted.

 

The TV Doesn’t Tell You How It’s Reading The Signal/ Quality

The main problem with the signal information bar on digital TV’s, Sky boxes, Freesat boxes is that it doesn’t actually tell you how its reading and measuring the signal. Most just give a percentage reading or signal bars and most don’t even tell you what frequency that it is reading so the TV could be tuned incorrectly and possibly causing poor TV reception and you wouldn’t necessarily know. If it doesn’t tell you how it’s measuring TV aerial/satellite signal strength & quality you not really going to know what it means and the results can be very misleading.

 

Some of the better TV’s will give you Bit Error Ratio (BER) information which is quite good really, but in all honestly after error correction, which is built into the broadcast signal you shouldn’t have any errors in your TV signal. If you do you will suffer effects like pixelation and even no TV picture at all. But if you have a poor digital TV/ satellite signal you will already know that you have a problem, so having a reading on your TV isn’t necessarily the biggest help in the world.

 

100% Signal Doesn’t Mean Anything Really 

Believe it or not signals are not measured in percentages so it’s very misleading to give signal information in this way. There isn’t really any such thing as a 100% signal. I will get to how signals are measured shortly.To say that a signal is 100% implies that it cannot be improved upon. You can always improve signal strength by installing a high-gain TV aerial or TV amplifier. Doing this isn’t always a good thing as you could have too much signal, yes that is a thing! Which itself can overload TV tuners, distribution equipment and cause TV picture break up. Which leads to if there is a minimum and maximum signal strength, where in the middle does 100% sit? The answer is that it doesn’t and it’s entirely down the TV software/ hardware and to what it determines and 100%. Like I said it doesn’t really mean anything.

 

Quality Is More Important Than Strength! 

It really does depend on the TV manufacturer, but you should always expect your TV signal to be 100% or a full signal bar. This usually means that at that time the received signal after error correction is fine and working as expected. If this is below 100% or jumping around you may find that you will have trouble with your TV reception. This could just be that the TV has stored the incorrect TV transmitter so I would check your TV tuning first. Also, it’s important to note that just because he signal reading says 100% atone time, it doesn’t necessarily that it will always be 100% and you could experience intermittent TV reception. Likewise, on other pieces of equipment like many Sky boxes, the signal quality may not be 100% or a full bar. This doesn’t mean that there is anything wrong with the signal, it could be reading the signal before error correction, which is actually a more reliable way of doing so. In conclusion, if you have a high percentage for quality and not for signal strength. I wouldn’t worry anymore about it if the TV picture is otherwise fine.

 

TV’s & TV/ Sat Receivers All Read Signals Different

You may plug a TV into one TV and has 100% signal strength and 100% signal quality. (quite common with the Humax Freesat boxes) and rightly think that everything is fine. Only to plug another TV in and get a much lower signal reading or vice versa. This is nothing really to worry about as it’s still the same signal going in but acts as any example of how different TV’s/ Set Top Boxes read and display the signal information differently. Unless of course when disconnecting one TV to fit the other you have inadvertently pulled the TV plug loose in which case you may need to fit a new coax plug or fit a new F plug.

 

TV Signal Strength Reading – Correct

To read a TV signal strength reading correct, you will need to know how these are measured. A TV signal is actually a voltage but to calculate signals and design TV systems could be very complex. Fortunately the dB with reference to micro-volts scale was introduced to greatly simply this and make the implementation of TV systems a case of simple adding and subtracting. I say simple, obviously there is far more to it than this. For you reference on the dB micro-volts scale. The scale starts at 0dB which would be 1 micro-volt, 60dB would be 1mV or 1000 micro-volts, 120 dB is 1000 mV or 1V and 180 dB is 1kV or 1000V. You can see that double at approx. 3dB increments, so 60dB is actually much, much more volts that double 30 dB. This means that when dealing with weak or borderline signal measurements a small improvement in dB can often make a big difference.

 

For you reference, suggested minimum signal strength levels are:

Terrestrial Digital TV – 45dB (Ideally no less than 50dB)

Analogue TV – 60dB

Satellite TV Signals – 47dB (Ideally no less no 52dB)

 

TV Signal Quality Reading – Correct

In regards to digital TV signals, the “quality” or robustness of a signal is measured in terms of actual signal strength minus electrical noise which can come from a wide range of interfering sources. The electrical noise will actually be present inside your signal so this is why relying on signal strength alone is not always a reliable determining factor of signal quality. That being said, the more signal that can be obtained from the TV transmitter the more protection you will have against electrical noise and interference.

 

There are a few ways that the signal quality can be measured:

 

Signal to noise ratio (S/N) – This measures the peak signal reading and the reading of the noise floor of the signal. Not be best way to measure signal quality as it doesn’t take into account noise within the signal.

 

Carrier to noise ratio (C/N) – An improvement of the signal to noise ratio in that it measures the noise of the signal floor immediately next to the signal being measured. This still doesn’t measure the noise inside the signal but gives a better idea as to what this typically will be.

 

Modulation Error Ratio (MER) – This is the best measurement for reliability of digital TV signals. This looks into the signal and measures noise inside the constellation. In effect this is the C/N reading with the noise inside the signal also measured and taken into effect.

 

Bit Error Ratio (BER) – Ultimately it all comes down the BER. There will always be errors in a digital signal. This is literally 0’s mixed up as 1’s and vice versa. The more information being compressed and carried inside a signal the more robust it needs to be. There is error correction built into the signal (Viterbi Error Correction or FEC) and after this has been taken into account (Post Viterbi Error Correction) there should be no errors inside the signal. Hence when you check the signal quality on your TV, PVR or STB is says 100% because it is reading no errors after error correction. If you have too many errors after error correction the TV picture will start to fail, pixleate and becoming blocky. If there are too many you will not get a TV picture at all. Before any error correction has been applied to a signal this is known as “channel BER” or CBER.

 

Will Adding A Amplifier Improve Signal Strength/ Quality? 

In theory the addition of a TV aerial amplifier or booster should increase the signal strength reading on your TV receiver as this will increase the signal strength when measured in dB, not easy if this is already at 100%.

 

Amplifiers are a good idea for overcoming signal losses associated with cable lengths and the splitting of TV signals and the closer the amplifier is installed to the aerial the better, providing there is at least 1m cable length between the two. You may need a masthead amplifier to be able to do this. The problem with adding a set back amplifier or TV aerial booster behind your TV is that although you will boost signal levels you will also introduce a load of electrical noise into the signal associated with the amplifier itself. Not only do amplifiers amplify the noise floor, which is not a problem as they amplify the signals you want as well. They also introduce their own noise figure which can reduce the carrier to noise or MER readings. Plus adding an amplifier could in some instances actually overload the TV equipment with too much signal which again can cause the digital picture to become blocky and pixelate.

 

Sometimes success can be achieved with amplifiers where the theory suggests that they shouldn’t where signals are very weak entering the TV tuner. Despite the amplifier introducing noise into the signal having that extra signal strength can help drive the signal through the parts and components of the TV. You may see any improvement in this situation but I wouldn’t hold your breath for reliable reception.

 

Are Signal Readings On TV's Reliable? 

All things considered the signal and quality readings on your TV should only ever be used as a very rough guide as you can see from the article there is so much more to this and without the correct equipment it is not possible to measure how good a TV signal is. There is one particular model of the early Panasonic Freesat TV’s that when plugged in and connected to a satellite dish it gives you 7 out of 10 for quality when there is nothing wrong. Unplug it and connect it to something like a Humax Freesat Foxsat box and you will get 100% and 100%. But like I said there is no such thing as a 100% signal.

 

TV Signal & Quality Questions – Post Them Below

I now write this at the bottom of all my blogs and articles but if you have any questions PLEASE DO NOT PHONE OUR TELEPHONE LINES OR FILL OUT WEBSITE CONTACT FORMS OR E-MAIL. All of these methods are reserved for customers only and if you’re after technical advice support you will either not receive a response or will receive one asking you to post your comment in the blog comment section. There are a few reasons for this. 1 – It gives me a central location to respond to all the questions that are asked, much quicker and easier for me. 2 – It’s actually good for the blog. 3- Everyone reading the blog will get the benefit of the question asked and the answer given. 4- It’s stops me having the answer the same questions over and over again. That being said I will help where I can providing your POST YOUR COMMENT IN THE BLOG COMMENTS SECTION. I also ask for your patience when doing so as I may not be able to respond as fast as you may like.

 

Until next time,

Tom

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