0% Signal Strength, 100% Signal Quality (1 Viewer)

[elsmandino]

Hi there,

I have been having a few problems with signal break up recently - particuarly on Dave, Really and Pick TV and started looking at my tuning details (I have my singal pointed at the Crystal Palace transmitter and hope that things shall settled down after the 18 April).

Anyway, I checked the Tuning details on Freeview BBC 1 and it said 0% Signal Strength, 100% Signal Quality. This channel never gets any breaking up, so why does it not give a reading for Signal Strength?

I then tried the same on a Freesat Channel and got 95% Strength, 100% Quality.

I then went back to have a look at Dave on Freeview and it said 6% Strength, 35% Quality.

Has anyone else been getting 0% Strength on a really strong freeview and channel?

 

[Jay_UK]

Hi there,

I was led to believe the strength/quality measures might not be worth the paper/screen they're written on. Its purely down to the driver/hardware vendor how they implement the scales/values and might not be accurate??

J.

ps - I can confirm there can big differences between scales with different makes of card/driver

 

[Paranoid Delusion]

http://www.ukfree.tv/txdetail.php?a=TQ339712

checkout the power, according to UKFreeview, power is down on all but 2 muxes, so Dave etc definitely affected

 

[elsmandino]

Thanks for that guys.

I guess I should just wait until my area has fully switched over next week when they whack up freeview to full power. I live fairly close to the transmitter so it probably won't matter if my aerial is pointing exactly at the transmitter - it should then give me a decent signal on all muxes.

One thing that I am worried about is that I am currently using an distribution amplifier that is connected to my external aerial and this feeds four TVs. How much of a boost does full power compare to the power that it is currently operating at?

Might the new signal be so powerful that combined with the amplifier, it overloads my TV receivers and I can't pick up anything?

 

[hairlesshobo]

Might the new signal be so powerful that combined with the amplifier, it overloads my TV receivers and I can't pick up anything?

If you start seeing symptoms like this when they knock it up to full power, you should be able to either a) remove the amplifier (may not be necessary any more), or b) get an inline attenuator to "soften" the signal coming in a little. An attenuator could put you back in the range that you are currently at now in regards to signal strength.

-Steve

 

[elsmandino]

Thanks for that.

It seems that I have been a little bit thick (no surprise there). According to the Crystal Palace website, one of their muxes is already operating at full power - 200,000 watts as opposed to 20,000. The mux that they did this to is the one that carries BBC ONE and TWO which I tested late last night and I have no problems at all with signal - no drop out at all, even with the amplifier on - which was the situation before the switchover began.

It might be that I over estimated how strong the signal was going to be. I have just tested how far I am from the transmitter and it says around 40km, plus I live in a bungalow, so my aerial is not quite as high as others might have it (it is on the end of a pole bolted to the side of my house).

This being the case, it will probably be the case that I could get away without using the booster and use a passive splitter instead - i.e. the booster is not really adding anything. I suppose it is a toss up as to whether I want so spend £5.00 or so a year on powering a splitter that is not really adding anything or whether I should spend £10 on a passive splitter that uses no power.

I would really like to do a proper comaprison between the amplifier and passive splitter just to see but as JAY says above (and I had heard this myself), software that provides an indicator of Strength/Quality is pretty much worthless.

Are there perhaps any cheap TV signal testers that are considered better than the others (I know that to get a really accurate signal, you need to spend £200, which is ridiculous).

Thanks

 

[hairlesshobo]

The best thing I know of for testing TV signal strength is an actual TV. The tuners in TVs are much better about not getting caught by dropped packets and just keep chugging through. When I am working on a antenna setup I always unplug from one of my tuner cards and plug the line into the cord instead, leaving everything else hooked up as is. If it works perfect on all channels that way, then I know if I have any issues it must be software related. I would love to buy a signal tester, but same as you, I don't want to spend insane amounts of money on something that isn't even useful for watching the channels being received

 

[elsmandino]

Thanks for that.
I have tried using the inbuilt tuner in my TV and it does seem to be giving a more comparable signal reading. On BBC 1 it is giving a signal strength of 86% and 70% on Dave.

Although there is no bar for signal quality, which I have never come accross before - only a bit error level bar, which stays at 0% on all channels. I guess that my best bet is to try both a passive splitter and the amplifier at different gain levels to get the highest strength I can without getting bit errors (which I think would start to go about 0% if the signal starts getting too strong).

 

[Branksome]

For information, on my Blackgold HD terrestrial tuner I also get a wrong signal strength. My local relay can give up to 100%/100% quality and signal strength as shown on the TV (after an aerial adjustment) and the same on my usb HD tuner connected to MediaPortal. But the Blackgold tuner typically shows somewhere between 0 and 5 signal but 100 for quality. Sometimes, on changing channels it will briefly show a strength of 80 before falling back to a single digit. I changed the connecting lead thinking that was the problem but I now assume it is just a faulty reading and I assume I can ignore it

Tom

 

[mm1352000]

Hi folks

Just a note on how we produce those readings. First, I quote the comments in the Microsoft BDA interface declaration (bdamedia.h).

Strength:

// Carrier strength in mDb (1/1000 of a DB).
//
// A strength of 0 is nominal strength as expected for the given
// type of broadcast network.
//
// Sub-nominal strengths are reported as positive mDb
//
// Super-nominal strengths are reported as negative mDb

Quality:

// Amount of data successfully extracted from the signal as a percent.
//
// Signal Quality is usually reported by the demodulation node and is
// a representation of how much of the original data could be extracted
// from the signal.
//
// In the case of Analog Signals, this percentage can be
// computed by examining the timing of HSync and VSync as will as by
// looking at information contained in HBlanking and VBlanking intervals.
//
// In the case of Digital Signals, this percentage can be
// computed by examining packet CRCs and FEC confidence values.
//
// 100 percent is ideal.
// 95 percent shows very little (almost unnoticable) artifacts when rendered.
// 90 percent contains few enough artifacts as to be easily viewable.
// 80 percent is the minimum level to be viewable.
// 60 percent is the minimum level to expect data services
// (including EPG) to work.
// 20 percent indicates that the demodulator knows that a properly modulated
// signal exists but can't produce enough data to be useful.

Most people who know a little about BDA and driver implementations will tell you that many driver implementations ignore the comments above and just give 0 - 100 readings as percentages. This being the case, MediaPortal's TV Server currently coalesces the readings to that range (ie. any reading less than 0 is bent up to 0, and any reading greater than 100 is bent down to 100). TV Server also calculates an average over all readings it finds, because tuners may actually offer multiple readings of strength and quality. That adjusted figure is what you get to see.

For analog signals, we have one measure: signal locked... or signal not locked. Locked -> 100% strength and quality; not locked -> 0%.

Rule of thumb:
- never compare readings between different tuners (even from the same manufacturer) unless they use the same tuner and demod chips driver (which is sometimes difficult to determine)
- quality is more important than strength in most cases

mm