The BBC and other broadcasters have it in some of their larger sites. Virgin Media cable systems use VHF frequencies everywhere.
TV Reception
- Thread starter idiott
- Start date
The BBC and other broadcasters have it in some of their larger sites. Virgin Media cable systems use VHF frequencies everywhere.
Sponsored Links
Right, so nowhere then that actually makes a damn bit of difference to the average TV viewer watching Freeview from their roof aerial . Yeah, that's what I thought. You're clutching at straws to justify a poor position.
What happens within the BBC's campus TV network has no bearing on what's broadcast from the UK's TV transmitter network. Particularly when one considers that modern TVs do not have a VHF TV tuner. As for Virgin, whatever happens with the transmitted signal up to the customer's modem or STB is Virgin's business. You'll also note that Virgin don't use B-L connectors. They use compression F connectors. So your justification on the grounds of VHF as far as consumer equipment goes is basically a load of B/S.
I thought we'd already put that to bed. My experience and that of Lucid proves otherwise.
This morning I ran what I think will be my final set of tests on this. The results settle the question to my own satisfaction. As far as makes any difference in the real world, there's no advantage with the CAI screen termination method over a pigtail.
I measured analogue and digital signals at low, medium and high settings: Analogue 30dB was determined by the point at which my Horizon meter would hold a stable signal lock. Analogue 47dB is the drop off (threshold) point. Analogue 60dB is the minimum recommended signal level for acceptable reception. Digital 26dB was the point where the TV began to display blocking from the Arqiver Mux. Digital 40dB is the minimum acceptable signal level for a DVB-T/T2 tuner. Digital 60dB is the mid point of the upper limit of the acceptable signal level limits and represents a strong signal.
The meter displays signal level in 1dB increments. That means for every whole dB displayed there's a subrange of values from .0 to .999 recurring befor the display tips up or down to the next whole dB value. It's sensible then to adjust up and down to the tipping point where the value changes and take two sets of readings to reflect the upper and lower limits of the whole dB point. So that's what I did using a 0-20dB variable attenuator in conjunction with fixed in-line attenuators to bring the signal in to a suitable adjustment range.
Before each set of final readings the meter and attenuators were left to settle for a period of a minute. Any fine adjustments were made if the level reading fluctuated over a tipping point, and then the equipment left to rest again before taking the final C/N and BER readings. I used averaging by noting the high and low points during three 30 second measuring periods over a 5 minute interval. Here are the results
It was suggested by Winston1 that at low signal levels the pigtail would perform significantly worse than a lead made the CAI way. This is the hypothesis being tested.
For analogue at 47 and 60 dBuV the results were identical. No difference, and the pictures looked the same subjectively. The only measured difference was when the signal was rendered unusable at 30 dBuV. Even then, the result was a 1dB signal difference in the audio signal level. When all said and done, the signal was already unusable with both cables, so a 1dB difference in level is pretty academic.
For digital at 40 and 60 dBuV neither connection method significantly outperformed the other. Even at 40 dBuV which is a below par signal level for digital, the predicted huge rise in bit rate error with the pigtail just wasn't apparent. Both cables still provided the set with enough signal and each resulted in a signal well within the performance window required for DVB-T/T2. What minor difference in BER is the equivalent of 1 additional bit error per million bits. Given that the threshold for BER error is 2 bits per 10,000, then the phrase "statistically insignificant" comes to mind. I won't dwell on the fact that the pigtail cable appeared to outperform the CAI method one at 60 dBuV.
The only time that BER rate showed an appreciable difference was when the digital signal was already very broken. If the picture is already pixelating and blocking with an BER of 510 errors per 10,000 bits then does it really matter if another cable is producing 580? I'm sure Winston1 will seize on this as irrefutable proof, but I can't help thinking that if you've already driven the car off the cliff then it's somewhat academic to be worrying about a scuff in the paintwork while plummeting to earth.
Final conclusion, when the chips are down a well made cable is a well made cable. The CAI method may well be superior in some theoretical circumstance or exotic application, but in the real world of consumer TV then is doesn't make any worthwhile difference.
I measured analogue and digital signals at low, medium and high settings: Analogue 30dB was determined by the point at which my Horizon meter would hold a stable signal lock. Analogue 47dB is the drop off (threshold) point. Analogue 60dB is the minimum recommended signal level for acceptable reception. Digital 26dB was the point where the TV began to display blocking from the Arqiver Mux. Digital 40dB is the minimum acceptable signal level for a DVB-T/T2 tuner. Digital 60dB is the mid point of the upper limit of the acceptable signal level limits and represents a strong signal.
The meter displays signal level in 1dB increments. That means for every whole dB displayed there's a subrange of values from .0 to .999 recurring befor the display tips up or down to the next whole dB value. It's sensible then to adjust up and down to the tipping point where the value changes and take two sets of readings to reflect the upper and lower limits of the whole dB point. So that's what I did using a 0-20dB variable attenuator in conjunction with fixed in-line attenuators to bring the signal in to a suitable adjustment range.
Before each set of final readings the meter and attenuators were left to settle for a period of a minute. Any fine adjustments were made if the level reading fluctuated over a tipping point, and then the equipment left to rest again before taking the final C/N and BER readings. I used averaging by noting the high and low points during three 30 second measuring periods over a 5 minute interval. Here are the results
It was suggested by Winston1 that at low signal levels the pigtail would perform significantly worse than a lead made the CAI way. This is the hypothesis being tested.
For analogue at 47 and 60 dBuV the results were identical. No difference, and the pictures looked the same subjectively. The only measured difference was when the signal was rendered unusable at 30 dBuV. Even then, the result was a 1dB signal difference in the audio signal level. When all said and done, the signal was already unusable with both cables, so a 1dB difference in level is pretty academic.
For digital at 40 and 60 dBuV neither connection method significantly outperformed the other. Even at 40 dBuV which is a below par signal level for digital, the predicted huge rise in bit rate error with the pigtail just wasn't apparent. Both cables still provided the set with enough signal and each resulted in a signal well within the performance window required for DVB-T/T2. What minor difference in BER is the equivalent of 1 additional bit error per million bits. Given that the threshold for BER error is 2 bits per 10,000, then the phrase "statistically insignificant" comes to mind. I won't dwell on the fact that the pigtail cable appeared to outperform the CAI method one at 60 dBuV.
The only time that BER rate showed an appreciable difference was when the digital signal was already very broken. If the picture is already pixelating and blocking with an BER of 510 errors per 10,000 bits then does it really matter if another cable is producing 580? I'm sure Winston1 will seize on this as irrefutable proof, but I can't help thinking that if you've already driven the car off the cliff then it's somewhat academic to be worrying about a scuff in the paintwork while plummeting to earth.
Final conclusion, when the chips are down a well made cable is a well made cable. The CAI method may well be superior in some theoretical circumstance or exotic application, but in the real world of consumer TV then is doesn't make any worthwhile difference.
Sponsored Links
The original analogue test only showed a difference when the cable's shielding was intentionally crippled. I don't share your view that a pigtail will eventually lose all contact with the plug. I'm of this view from more than a quarter century in the AV and electronics trade. SamGanges is of the same view. Satcure is of the same view, as are the guys at Aerials and TV. It's the difference between theoretical possibilities and the practical realities of the real world. The CAI way may well be superior in some theoretical sense. But your assertion that the pigtail method isn't sufficient just doesn't hold water. Sorry, but thems the facts. The difference is that me, SamGanges, Satcure, the guys at Aerials and TV and I bet a whole load more respected individuals and businesses in the trade think for ourselves and test things in practise rather than being lead like a sheep.
As for your waffle about "immediate difference" and something to do with driving....
1) You misquoted me. I said "make an improvement" not immediate benefit. That doesn't preclude me from adopting something that does provide an immediate benefit, but it's not what I said.
I use compression connectors because they provide a robust connection that maintains the shielding right down to the tip of the plug and they get closer to a true 75 Ohm coax plug than a Belling-Lee. They're tamper-proof too which is a nice side benefit. I'd be perfectly willing to use the CAI method for B-Ls except for two reasons: I'm not a fan of soldered solid core centre pins inside cable bodies that can be unscrewed. That's just personal preference. Second, it doesn't offer any advantage over my tried and tested method. That was my gut instinct before this debate. The measurements I made appear to bear that out.
2) I have no clue what your rant about seatbelts and mobile phones has to do with anything here.
Your tests are still invalid because you have not tested when the pigtail loses contact with the metal body of the plug as it invariably intermittently does.
Horrors it seems to be worse. It appears you don't even solder the centre pin. Are you serious? Non soldered centre pins are a prime cause of failure of magic eyes and masthead amplifiers.
Quarter of a century in the trade and you haven't learnt how to properly fit a B/L plug. Well I've been over half a century in the trade (since 1961) and learnt how to fit them in those early days. Yes I remember 405 at VHF, 625 at VHF (still broadcast in some countries), and now there is DVB-T at VHF in parts of Europe.
Horrors it seems to be worse. It appears you don't even solder the centre pin. Are you serious? Non soldered centre pins are a prime cause of failure of magic eyes and masthead amplifiers.
Quarter of a century in the trade and you haven't learnt how to properly fit a B/L plug. Well I've been over half a century in the trade (since 1961) and learnt how to fit them in those early days. Yes I remember 405 at VHF, 625 at VHF (still broadcast in some countries), and now there is DVB-T at VHF in parts of Europe.
I think we already explained - several times - that it doesn't (and, even if it did, the capacitative coupling is sufficiently high at UHF frequencies for the signal to be unaffected).
Why do I need to solder the centre pin when RF2 out requires a female B-L and I use female B-L with a screw connection for centre, or I use a compression fit plug/socket.
Why do I need to solder B-L centre pins for a masthead amp or magic eye when all the gear I buy and fit comes with F connections as standard - including the incommer on magic eyes.
In fact, other than the connection to a TV or a DVB-T recorder, is there really that much now that still uses B-L in a domestic aerial distribution chain?
What he said ^
But he has already shown (in his tests) that UHF analogue is affected if the screen is open circuit.
Capacitive coupling will not work at DC and DC is required to power a masthead amp. The DC for this sometimes comes from the TV itself.
Because in some cases the TV or set top box provides the DC for the mast head amplifier. Is is also good practice to solder the centre pin. Not soldering is the sign of a cowboy.
Which TVs and set top boxes do that?
Your problem seems to be getting past the idea that a well executed pigtail provides every bit as effective shield coupling to the plug as the CAI method.
[/quote]Which TVs and set top boxes do that?[/quote]
You mean you have been in the trade 25 years and have never come across this feature?
Thecnika STBHDIS2010
Woolworths Worthit set top box.
Fortec Star FS-2100
Fortec Star FS-3100
Various Lidl set top boxes.
Some LG TVs.
You mean you have been in the trade 25 years and have never come across this feature?
Thecnika STBHDIS2010
Woolworths Worthit set top box.
Fortec Star FS-2100
Fortec Star FS-3100
Various Lidl set top boxes.
Some LG TVs.
[/quote]
Your problem seems to be getting past the idea that a well executed pigtail provides every bit as effective shield coupling to the plug as the CAI method.[/quote]
The fact of the matter is it does not. Copper oxidises over time and contact is lost. The pigtail itself is an inductive loop, all be it with shorted turns until oxidation occurs.
Your problem seems to be getting past the idea that a well executed pigtail provides every bit as effective shield coupling to the plug as the CAI method.[/quote]
The fact of the matter is it does not. Copper oxidises over time and contact is lost. The pigtail itself is an inductive loop, all be it with shorted turns until oxidation occurs.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
