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Thread: Signal Strength Vs Signal Quality

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    Default Signal Strength Vs Signal Quality



    Hi All,
    I've been experiencing some reception problems lately (mainly on the 7 channels). My Panasonic TV has a "Signal Condition" meter. It's showing full signal strength for all channels, however the signal quality for ch7 is jumping between bad and poor.

    So my question is: what's the difference between strength and quality and how can you have poor signal quality when you've got good signal strength?

    /Gavin
    “There are 10 types of people in this world, those who understand binary – and those who don’t”



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    Just curious as to what you mean by 'Poor Quality', Pixeling, Freezing, Grainyness or ???

    MTV and the other Guru's can explain this expertly and I am NOT suggesting what I say is correct but you can have a transmitter running at full power but the signal it carries can be poor.
    If it is affecting other people, then the problem is at the studio end but if its only you and the one TV, then its at your end and you will need to check everything out to find the problem.
    Last edited by gordon_s1942; 19-03-11 at 12:55 PM.
    I stand unequivicably behind everything I say , I just dont ever remember saying it !!

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    Premium Member mickstv's Avatar
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    Way too much signal could cause overload of the tuner module it will show plenty of signal but your quality will turn to sh!t because of all the errors in the transmission.

    Have you got a mast head amp. If so open it up and turn the gain controls down to at least half level and see what happens.

    If you have no mast head amp you could try an inline attenuator to reduce the level of signal coming in.




    Mick
    Last edited by mickstv; 19-03-11 at 01:45 PM.

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    In simple terms, signal strength is just that, the digital channel power being received from the transmitter. Signal quality: (think: digital data streams) is how much of the data in that stream is able to be decoded without (or with a minimum) of errors.
    The reason for errors can be many and varied; multipath/reflected signals, interference, substandard cabling, tropospheric ducting etc etc....

    Michael
    Last edited by michael_sa; 19-03-11 at 03:56 PM.

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    Signal strength was all-important with analogue, but less important with digital.

    The signal strength is the digital channel power... which carries the signals.

    Signal quality is made up of several aspects, the most important being the Bit Error Ratio (BER) which is the measurement of how many errors there are in the digital data stream.

    There are different levels of error correction a digital tuner applies to signals that contain errors, but when there are too many errors happening too fast for the error-correction system to keep up, that's when you get pixelation or loss of reception altogether.

    Signal strength and signal quality do not always relate directly to each other with increases/decreases.

    You can have excellent signal quality with low signal strength, but you can have (as you've seen) high signal strength with poor signal quality.

    So whilst the signal 'strength' is delivering the signals OK, those signals have become corrupted, resulting in poor signal 'quality'.

    Something is happening to cause your signal quality to drop, which means there will be an increase in the BER.

    As mentioned, overly-strong signals can cause this, as can many other things, like reflected/multipath signals, wind moving trees around, interference from other RF, atmospheric and electrical sources, poor-quality cabling and connections, etc.

    Yes, it's not uncommon for these to produce issues with one frequency (eg Ch 7 multiplex) and not others.

    There could be any number of reasons, or a combination of them causing your issue.

    As mentioned, you can experiment with various adjustments, attenuation etc and you might get lucky and solve the issue, however, to be able to know exactly what the cause of the problem is and then, how to best resolve it, you need to obtain accurate signal measurements.

    The 'scales' measurements in TV tuners are only a rough estimation and are not accurate.

    A professional digital meter/spectrum analyser will indicate where the problem is, then knowledge and experience would tell an installer what to do to rectify the problem/s.

    Sometimes even moving an antenna position just a few centimetres in any direction, including up/down can make all the difference.

    Unfortunately, without the instrumentation connected whilst making the adjustments, it's just guessing/experimenting.

    Perhaps if you mention your suburb, what make/model of antenna you're using, how it's mounted and which transmission site you're pointing it at (eg: Mt Lofty) plus any info on the type of coax eg: RG6 Quadshield, details of any amps or splitters used, etc, can help, but nothing beats actually being there with instrumentation 'seeing' exactly what your signals are doing.

    You can start by ensuring you have good-quality flyleads, eg: RG6 Quadshield, as cheap poorly-shielded flyleads can pick up lots of interference from other cabling, powerpacks, other equipment in close proximity to them.

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    Quote Originally Posted by gordon_s1942 View Post
    Just curious as to what you mean by 'Poor Quality', Pixeling, Freezing, Grainyness or ???
    Hhmm, Thank all.

    Gordon: the signal condition meter on my Panasonic TV changes color from Red-Yellow-Green.
    Red=Bad
    Yellow=Poor
    Green=Good

    mtv: My antenna is pointing at Grenfell St (I'm in the Adelaide Hills). I have considered replacing the coax. Should I be using RG6 or RG59?
    “There are 10 types of people in this world, those who understand binary – and those who don’t”

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    Quote Originally Posted by mtv View Post
    Signal strength was all-important with analogue, but less important with digital.


    Digital tuner modules are much the same as the analogue versions and they both can suffer from overloading and this will lead to signal quality problems.





    Mick

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    Quote Originally Posted by mickstv View Post
    Digital tuner modules are much the same as the analogue versions and they both can suffer from overloading and this will lead to signal quality problems.

    Mick
    Overloading signals can indeed cause problems for any tuner, but with digital, the operating 'window' of acceptable levels is much smaller than analogue, meaning there is a fine line between perfect reception and no reception.

    With analogue, there is a gradual deterioration with signal fluctuations, with digital, it can be perfect one second, and nothing the next.

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    Quote Originally Posted by GavinSV View Post
    mtv: My antenna is pointing at Grenfell St (I'm in the Adelaide Hills). I have considered replacing the coax. Should I be using RG6 or RG59?
    Use RG6 Quadshield with 'F' connectors.

    I doubt you have a signal overload from the Grenfell St translators, unless you are using an amplifier (which you didn't mention) as the Grenfell St translators are 1kw compared to the main transmitters on Mt Lofty which are 50kw for the VHF channels and 200kw for SBS (UHF)

    You most-likely need a horizontally polarised high-gain Band 5 yagi, or UHF phased array antenna for Grenfell St.

    As I mentioned, antenna mounting position can make a huge difference to performance.

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    Quote Originally Posted by mtv View Post
    Overloading signals can indeed cause problems for any tuner, but with digital, the operating 'window' of acceptable levels is much smaller than analogue, meaning there is a fine line between perfect reception and no reception.

    With analogue, there is a gradual deterioration with signal fluctuations, with digital, it can be perfect one second, and nothing the next.


    That will be the case with fringe reception when you will generally have a poorer CNR for various reasons including booster noise, poor quality cable and multipath signal conditions.


    But I believe the digital cliff edge will be less of an issue in better reception areas. The higher level of signal and internal AGC should be able to compensate for most signal level issues except for Overload.


    Mick
    Last edited by mickstv; 19-03-11 at 10:19 PM.

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    Quote Originally Posted by mickstv View Post
    That will be the case with fringe reception when you will generally have a poorer CNR for various reasons including booster noise, poor quality cable and multipath signal conditions.


    But I believe the digital cliff edge will be less of an issue in better reception areas. The higher lever of signal and internal AGC should be able to compensate for most signal level issues except for Overload.

    Mick
    The digital cliff is the same, regardless of reception area, as we've already discussed, the reliability of digital signals is more about BER/MER & NM than DCP, however, sufficient DCP 'at the antenna' is still a requirement.

    Naturally, if DCP is below the minimum for a lock, then that's certainly below the digital cliff.

    I agree with you on the AGC, especially with overload, but even the AGC isn't going to do jack if there's poor signal 'quality'.

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    Ok i'll admit defeat as I cannot compete due to my inferior intelligence regarding this topic, i'll go back to my TV's and computers.



    Mick

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    Quote Originally Posted by mickstv View Post
    Ok i'll admit defeat as I cannot compete due to my inferior intelligence regarding this topic, i'll go back to my TV's and computers.

    Mick
    It's all good, Mick....

    I appreciate you're input, mate.

    Just to clarify, you are correct that the digital cliff edge is easier to control in good signal areas, as there will be a greater margin, however, the minimum signal requirements still remain the same, regardless of good or poor signal 'areas'.

    You've raised some good points and there are some similarities between analogue & digital signals, but the majority are quite different.

    For example, for the same 7MHz bandwidth used for TV in Australia, analogue uses 1 (vision) carrier per channel, whereas the DVB-T digital standard uses 6817 carriers per 7MHz mux. Add to that the symbol rate and guard interval.

    This is commonly referred to as the 8k mode, which we use in Australia.

    Being an area which I specialise in, I could go a lot more into depth on the subject, but was originally trying to keep the explanation relatively simple for the OP.

    Cheers

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    Quote Originally Posted by mtv View Post
    I doubt you have a signal overload from the Grenfell St translators, unless you are using an amplifier (which you didn't mention)
    Sorry, forgot to mention, yes there is a mast head amp which I noticed has a gain control pot. I turned the gain up a bit yesterday, which appeared to improve reception.


    Quote Originally Posted by mtv View Post
    You most-likely need a horizontally polarised high-gain Band 5 yagi, or UHF phased array antenna for Grenfell St.
    I think my antenna is a phased array antenna. It looks like this:
    “There are 10 types of people in this world, those who understand binary – and those who don’t”

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    Quote Originally Posted by GavinSV View Post
    I think my antenna is a phased array antenna. It looks like this:
    Is your antenna in the same orientation as the one in the picture you linked to? (that one is vertically polarised)
    As mtv mentioned, yours should be horizontally polarised () for Grenfell St transmitters.

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    Quote Originally Posted by michael_sa View Post
    Is your antenna in the same orientation as the one in the picture you linked to? (that one is vertically polarised)
    As mtv mentioned, yours should be horizontally polarised () for Grenfell St transmitters.
    Yeah, I thought that picture might cause confusion after I posted it, but no, my antenna is turned 90 degrees (ie horizontal). Sorry, It was the only picture I could find. -Cheers
    “There are 10 types of people in this world, those who understand binary – and those who don’t”

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    Quote Originally Posted by GavinSV View Post
    Yeah, I thought that picture might cause confusion after I posted it, but no, my antenna is turned 90 degrees (ie horizontal). Sorry, It was the only picture I could find. -Cheers
    Yeah I thought it'd prob be correct, but was worth asking the question.

    You mentioned having a mast-head amp - have you confirmed that it is powered up? - I know you mentioned adjusting the gain and you thought it improved...
    Does the amp have a LED to indicate that it's powered on?
    Does turning it's power supply off make any difference to your reception?

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    Gavin, when I asked origonaly what you meant by 'Poor' I meant what YOU were seeing on the screen of your TV not the bars on a inbuilt meter because at best, they are just a guide.
    Mine here dance around like whirling dervishes on each channel depending on the time of day and weather conditions so once you know you have the absolute best your going to get, then try not to look at the meter too often unless there is major signal loss.
    I stand unequivicably behind everything I say , I just dont ever remember saying it !!

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    Quote Originally Posted by gordon_s1942 View Post
    Gavin, when I asked origonaly what you meant by 'Poor' I meant what YOU were seeing on the screen of your TV not the bars on a inbuilt meter because at best, they are just a guide...
    Good point, he hasn't actually stated that he's getting pixelation or loss of signal.
    Last edited by michael_sa; 20-03-11 at 11:16 AM.

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    Quote Originally Posted by michael_sa View Post
    Good point, he hasn't actually stated that he's getting pixelation or loss of signal.
    Yeah, fair question. When this reception issue began, ch7 was experiencing severe pixelation or the picture would drop out altogether. That's when I started looking at the signal condition meter.

    The amp is definitely working. When I turn off its power supply all channels disappear.
    “There are 10 types of people in this world, those who understand binary – and those who don’t”

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