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Quad shield coax & dielectric?
In message , Brian
Morrison writes On Fri, 14 Mar 2014 15:51:51 -0700 Bob E. wrote: 75-ohm RG-6 coax: quad shield differs from "standard" RG-6 in that the dielectric is reduced in diameter to accomodate the extra shielding. How does this affect the performance? I'm looking at 1 GHz (HDTV use). Thanks. If the dielectric is reduced in diameter then to maintain the same Zo for the same Er the inner conductor will have to be reduced in diameter too. This will tend to increase the loss in the cable because of the increased resistive losses and the dielectric loss will be higher because the field is more concentrated in the dielectric. What is your prime requirement? Do you need the low loss or the good screening more? See existing thread. -- Ian --- news://freenews.netfront.net/ - complaints: --- |
Quad shield coax & dielectric?
On 17/03/2014 13:14, Jerry Stuckle wrote:
On 3/17/2014 3:45 AM, Jeff wrote: 7dBm is an absolutely colossal signal for a TV set. Even 0dBm is an absolutely colossal signal! Not in the United States. It was the minimum that the cable industry provides to the TV set. We are talking a signal 4.25Mhz wide signal, not SSB or CW. dBm is not a bandwidth dependant measurement such as CNR which is. Putting +7dBm into a tv receiver is madness, it would cause severe overload and inter mods. +7dBm is 50mW and that equates to about 61mV in a 75 ohm system which is an enormous signal. Jeff Wrong. TV's are made to handle at least 20 dbm. And cable tv companies must deliver at least 10 dbm to the premises. TV signals (at least in the U.S.) are not measured by CNR - they are measured by dbm. CNR is not important because the bandwidth does not change. Your insistence on using CNR shows you know nothing about how the industry measures signal strength. I have not insisted that CNR was used, it that was another poster who mentioned CNR, what I was pointing out was the error that you made in taking the 43db CNR value that was posted and then going on about dbMmlevels. I also dispute that televisions are made to handle +20dBm; that is 100mW far in excess of what a tv tuner can handle without overload!!!! +20dbmV may be but not +20dbm. Jeff |
Quad shield coax & dielectric?
On 3/17/2014 11:32 AM, Ian Jackson wrote:
In message , Jerry Stuckle writes On 3/17/2014 3:45 AM, Jeff wrote: 7dBm is an absolutely colossal signal for a TV set. Even 0dBm is an absolutely colossal signal! Not in the United States. It was the minimum that the cable industry provides to the TV set. We are talking a signal 4.25Mhz wide signal, not SSB or CW. dBm is not a bandwidth dependant measurement such as CNR which is. Putting +7dBm into a tv receiver is madness, it would cause severe overload and inter mods. +7dBm is 50mW and that equates to about 61mV in a 75 ohm system which is an enormous signal. Jeff Wrong. TV's are made to handle at least 20 dbm. And cable tv companies must deliver at least 10 dbm to the premises. You do realise that 20dBm (appx 68dBmV) is a massive 100mW? With a modest 50 channel analogue cable TV system, that would be a total input power of 5W - which would have a TV set or set-top box sagging at the knees - if not even beginning top smoke! TV signals (at least in the U.S.) are not measured by CNR Well of course they aren't. CNR is a ratio - not a level. - they are measured by dbm. No. The US and UK cable TV industry definitely uses dBmV. Which is generally shortened to dbm here. What you are talking about is dBmW - which, unfortunately, is also often shortened to dBm. But most people on this side of the pond who are in the business understand that. 0dBmV is 1mV - a reasonable signal to feed to a TV set (especially directly from an antenna). 0dBm is appx 48dBmV (250mV) - and that's one hell of a TV signal! With a 75 ohm source impedance (antenna and coax) - and no significant levels of outside noise-like interference, a 0dBmV (1mV) analogue NTSC signal, direct from an antenna, will have a CNR of around 57dB. A TV set with a decent tuner noise figure (5dB?) or a set-top box (8dB) will produce essentially noise-free pictures. However, with an analogue TV signal from a large cable TV system, the signal CNR will be much worse than 57dB (regardless of its level). If I recall correctly, the NCTA ( National Cable Television Association) minimum spec is a CNR of 43dB (UK is 6B). At this ratio, it is judged that picture noise is just beginning to become visible. CNR is not important because the bandwidth does not change. You're havin' a laff - surely?! Nope. Your insistence on using CNR shows you know nothing about how the industry measures signal strength. I'm not insisting on anything. However, an analogue with a poor CNR will produce noisy pictures - regardless of the signal level. Similarly, a digital signal with a too poor an SNR/MER will fail to decode - regardless of the signal level. I think the UK cable TV spec for digital signals is 25dB (although a good set-top box will decode down to the mid-teens). External noise is somewhat consistent. Front ends are pretty much comparable in their S/N ratio. The only problems with noise are generally if you have something generating noise locally. But that is not a problem with the signal nor the receiver. That is why the real world uses signal strength to determine proper signal levels. CNR in TV is not used nor is it required when the other parameters are known. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Quad shield coax & dielectric?
On 3/17/2014 11:43 AM, Ian Jackson wrote:
In message , Jerry Stuckle writes On 3/17/2014 3:38 AM, Jeff wrote: No one said the NTSC had to be noiseless. But the 43dB is a bit high, even for older sets. Input from the cable tv company to our equipment was 10-20dB; we tried to push 10dB to all of the outputs but never had a problem even down to 7dB (the lowest we would let it drop to). That makes no sense; a 7dB CNR would be pretty much unwatchable on analogue, it would be a very very noisy picture, if it even locked at all! Jeff I'm not talking CNR - I'm talking signal strength. 7dbm is plenty of signal. Most later TV's would work even at 0dbm. Well the "43dB"that you were stating "was a bit high" was expressed as CNR, so it is reasonable to think that your other figures were also CNR as you did bot state otherwise. Also 7dBm (5mW) is a very high signal and would cause most sets to intermod like crazy. Perhaps you meant 7dBmV. Jeff Yes, I should have been more clear. It is 7dBmV - but the TV industry generally shortens it to dbm (and that's how the test equipment is labeled). Just like other industries which use dBmW generally shortens it to dbm. No. You are absolutely wrong. No one in the professional cable TV would even think of referring to 'dBmV as 'dBm'. There's around 48dB difference between the two. Then why, pray tell, does the several $K Sencore signal analyzer sitting on the back shelf (because it's now pretty much obsolete) say "dbm"? It has been that way since I first started with MATV systems back in the early 70's. It's so common many cable techs wouldn't know there even is a dBmW. However, you are right about 'dBmW' - which is invariably (and regrettably) shortened to 'dBm'. Sorry for the confusion - it's been about 10 years since I've been in the field - I've been away from it for too long. Well, I think it is beginning to show! [Sorry for being personal, as it's something I always try to avoid.] I've been in management for several years now. I still get out in the field some - but I'm too old to be pulling cables. Leave it to the youngsters. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Quad shield coax & dielectric?
On 3/17/2014 11:58 AM, Jerry Stuckle wrote:
Then why, pray tell, does the several $K Sencore signal analyzer sitting on the back shelf (because it's now pretty much obsolete) say "dbm"? It has been that way since I first started with MATV systems back in the early 70's. It's so common many cable techs wouldn't know there even is ^ company a dBmW. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Quad shield coax & dielectric?
Jerry Stuckle wrote:
On 3/17/2014 10:45 AM, Rob wrote: Jerry Stuckle wrote: On 3/16/2014 11:42 AM, Ian Jackson wrote: In message , Jerry Stuckle writes HDTV requires a stronger signal than the old NTSC. It really depends on how good your old analogue NTSC was. For a noiseless picture, you would need around 43dB CNR, but pictures were still more-than-watch-able at 25dB, and the picture was often still lockable at ridiculously low CNRs (when you certainly wouldn't bother watching it). Digital signals can work at SNRs down to around 15dB for 64QAM and 20dB for 256QAM (although if it's a little below this, and you will suddenly get nothing). That has not been our experience. We had a number of customers here in the DC area who had great pictures on NTSC sets, but got either heavy pixilation or no picture at all when the switchover occurred. We sent them to a company which does tv antenna installations (we do a lot of low voltage, including tv - but not antennas). In every case, installing a better outdoor antenna solved the problem. Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. |
Quad shield coax & dielectric?
Ian Jackson wrote:
Yes, I should have been more clear. It is 7dBmV - but the TV industry generally shortens it to dbm (and that's how the test equipment is labeled). Just like other industries which use dBmW generally shortens it to dbm. No. You are absolutely wrong. No one in the professional cable TV would even think of referring to 'dBmV as 'dBm'. There's around 48dB difference between the two. However, you are right about 'dBmW' - which is invariably (and regrettably) shortened to 'dBm'. I think here it is more customary to express voltage levels in dBuV. |
Quad shield coax & dielectric?
In message , Jerry Stuckle
writes On 3/17/2014 11:32 AM, Ian Jackson wrote: In message , Jerry Stuckle writes On 3/17/2014 3:45 AM, Jeff wrote: 7dBm is an absolutely colossal signal for a TV set. Even 0dBm is an absolutely colossal signal! Not in the United States. It was the minimum that the cable industry provides to the TV set. We are talking a signal 4.25Mhz wide signal, not SSB or CW. dBm is not a bandwidth dependant measurement such as CNR which is. Putting +7dBm into a tv receiver is madness, it would cause severe overload and inter mods. +7dBm is 50mW and that equates to about 61mV in a 75 ohm system which is an enormous signal. Jeff Wrong. TV's are made to handle at least 20 dbm. And cable tv companies must deliver at least 10 dbm to the premises. You do realise that 20dBm (appx 68dBmV) is a massive 100mW? With a modest 50 channel analogue cable TV system, that would be a total input power of 5W - which would have a TV set or set-top box sagging at the knees - if not even beginning top smoke! TV signals (at least in the U.S.) are not measured by CNR Well of course they aren't. CNR is a ratio - not a level. - they are measured by dbm. No. The US and UK cable TV industry definitely uses dBmV. Which is generally shortened to dbm here. I must emphasise that you are simply WRONG. None of the professional cable TV engineers I've ever been associated with (both in the UK and the USA have ever used the term 'dBm' when they mean 'dBmV'. Can you think of a reason why? [Clue - There's 48dB difference between the two units.] What you are talking about is dBmW - which, unfortunately, is also often shortened to dBm. But most people on this side of the pond who are in the business understand that. I can live with that. The incorrect use of 'dBm' to mean 'dBmW' is a de facto industry standard - and I'm not going to try and change the world by pretending that I don't understand the incorrect 'dBm'. 0dBmV is 1mV - a reasonable signal to feed to a TV set (especially directly from an antenna). 0dBm is appx 48dBmV (250mV) - and that's one hell of a TV signal! With a 75 ohm source impedance (antenna and coax) - and no significant levels of outside noise-like interference, a 0dBmV (1mV) analogue NTSC signal, direct from an antenna, will have a CNR of around 57dB. A TV set with a decent tuner noise figure (5dB?) or a set-top box (8dB) will produce essentially noise-free pictures. However, with an analogue TV signal from a large cable TV system, the signal CNR will be much worse than 57dB (regardless of its level). If I recall correctly, the NCTA ( National Cable Television Association) minimum spec is a CNR of 43dB (UK is 6B). At this ratio, it is judged that picture noise is just beginning to become visible. CNR is not important because the bandwidth does not change. You're havin' a laff - surely?! Nope. OK. Are you by any chance related to John McEnroe? http://www.youtube.com/watch?v=ekQ_Ja02gTY Your insistence on using CNR shows you know nothing about how the industry measures signal strength. I'm not insisting on anything. However, an analogue with a poor CNR will produce noisy pictures - regardless of the signal level. Similarly, a digital signal with a too poor an SNR/MER will fail to decode - regardless of the signal level. I think the UK cable TV spec for digital signals is 25dB (although a good set-top box will decode down to the mid-teens). External noise is somewhat consistent. Front ends are pretty much comparable in their S/N ratio. The only problems with noise are generally if you have something generating noise locally. But that is not a problem with the signal nor the receiver. That is why the real world uses signal strength to determine proper signal levels. CNR in TV is not used nor is it required when the other parameters are known. So pray tell me why, in my many years in the cable TV industry, I spent so many pointless hours measuring (among all the other parameters) CNR? -- Ian |
Quad shield coax & dielectric?
On 17/03/2014 16:01, Jerry Stuckle wrote:
On 3/17/2014 11:58 AM, Jerry Stuckle wrote: Then why, pray tell, does the several $K Sencore signal analyzer sitting on the back shelf (because it's now pretty much obsolete) say "dbm"? It has been that way since I first started with MATV systems back in the early 70's. It's so common many cable techs wouldn't know there even is I can't comment onyour Sencore signal analyzer as I have never used one, BUT every other signal generator and spectrum analyser I have come across and used, from HP/Agilent, R&S, MI etc etc when labelled dBm mean dB relative to a milliwatt. Also every other RF engineer I have come across universally understands dBm to mean dB relative to a milliwatt NOT dBmV. Just check the specs of any rf test gear line you will see that they refer to dbm meaning dB relative to a milliwatt. Even Sencore's website with the specs of their latest equipment, Where they mean dBuV or dBmV they say so. Jeff |
Quad shield coax & dielectric?
In message , Rob
writes Jerry Stuckle wrote: On 3/17/2014 10:45 AM, Rob wrote: Jerry Stuckle wrote: On 3/16/2014 11:42 AM, Ian Jackson wrote: In message , Jerry Stuckle writes HDTV requires a stronger signal than the old NTSC. It really depends on how good your old analogue NTSC was. For a noiseless picture, you would need around 43dB CNR, but pictures were still more-than-watch-able at 25dB, and the picture was often still lockable at ridiculously low CNRs (when you certainly wouldn't bother watching it). Digital signals can work at SNRs down to around 15dB for 64QAM and 20dB for 256QAM (although if it's a little below this, and you will suddenly get nothing). That has not been our experience. We had a number of customers here in the DC area who had great pictures on NTSC sets, but got either heavy pixilation or no picture at all when the switchover occurred. We sent them to a company which does tv antenna installations (we do a lot of low voltage, including tv - but not antennas). In every case, installing a better outdoor antenna solved the problem. Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. That's quite s drop in power. In the UK, it seems that the digitals are being run at 1/5th of what the analogues were. Certainly the main transmitter for London, Crystal Palace, was 1MW erp, but is now 200kW on the main six digital muxes. [There are also a couple more running around 10dB less.] -- Ian |
Quad shield coax & dielectric?
Ian Jackson wrote:
Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. That's quite s drop in power. In the UK, it seems that the digitals are being run at 1/5th of what the analogues were. Certainly the main transmitter for London, Crystal Palace, was 1MW erp, but is now 200kW on the main six digital muxes. [There are also a couple more running around 10dB less.] When received with a similar quality setup as was required for longer distance analog reception, the power is adequate. Of course it does not allow indoor reception at 50km distance, but in the areas where indoor reception is advertised there are local transmitters. "the countryside" still needs a roof-mounted yagi, but they always did. (I think the spec was a yagi at least 1.5m above the roof and 12m above the ground) Of course the 1MW was peak envelope power (at the sync pulses), with a mean power a lot less than that (for typical content). |
Quad shield coax & dielectric?
In message , Rob
writes Ian Jackson wrote: Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. That's quite s drop in power. In the UK, it seems that the digitals are being run at 1/5th of what the analogues were. Certainly the main transmitter for London, Crystal Palace, was 1MW erp, but is now 200kW on the main six digital muxes. [There are also a couple more running around 10dB less.] When received with a similar quality setup as was required for longer distance analog reception, the power is adequate. Of course it does not allow indoor reception at 50km distance, but in the areas where indoor reception is advertised there are local transmitters. "the countryside" still needs a roof-mounted yagi, but they always did. (I think the spec was a yagi at least 1.5m above the roof and 12m above the ground) Of course the 1MW was peak envelope power (at the sync pulses), with a mean power a lot less than that (for typical content). That is indeed true. The UK black level (which is when the highest average power is being transmitted) is 2.4dB below sync - and peak white (minimum power) is 14dB below sync. Even allowing for the relatively high average power during the vertical interval, it's obviously the average TV programme will consume a lot less power than if the transmitter was pumping out full envelope power all the time. Of course, the 1MW is erp, and as the transmitting antenna gains can be considerable, the transmitter won't be putting out 1MW. But again, you've got combiner losses and feeder losses ....... -- Ian |
Quad shield coax & dielectric?
On 3/17/2014 12:15 PM, Ian Jackson wrote:
In message , Jerry Stuckle writes On 3/17/2014 11:32 AM, Ian Jackson wrote: In message , Jerry Stuckle writes On 3/17/2014 3:45 AM, Jeff wrote: 7dBm is an absolutely colossal signal for a TV set. Even 0dBm is an absolutely colossal signal! Not in the United States. It was the minimum that the cable industry provides to the TV set. We are talking a signal 4.25Mhz wide signal, not SSB or CW. dBm is not a bandwidth dependant measurement such as CNR which is. Putting +7dBm into a tv receiver is madness, it would cause severe overload and inter mods. +7dBm is 50mW and that equates to about 61mV in a 75 ohm system which is an enormous signal. Jeff Wrong. TV's are made to handle at least 20 dbm. And cable tv companies must deliver at least 10 dbm to the premises. You do realise that 20dBm (appx 68dBmV) is a massive 100mW? With a modest 50 channel analogue cable TV system, that would be a total input power of 5W - which would have a TV set or set-top box sagging at the knees - if not even beginning top smoke! TV signals (at least in the U.S.) are not measured by CNR Well of course they aren't. CNR is a ratio - not a level. - they are measured by dbm. No. The US and UK cable TV industry definitely uses dBmV. Which is generally shortened to dbm here. I must emphasise that you are simply WRONG. None of the professional cable TV engineers I've ever been associated with (both in the UK and the USA have ever used the term 'dBm' when they mean 'dBmV'. Can you think of a reason why? [Clue - There's 48dB difference between the two units.] We aren't talking professional cable TV engineers here. We are talking installers and cable pullers (a much larger group, BTW). They barely know what a volt is - much less the difference between dBmW and dBmV. TV technicians at least know what a volt is. But most of them don't know the difference between dBmV and dBmW. What you are talking about is dBmW - which, unfortunately, is also often shortened to dBm. But most people on this side of the pond who are in the business understand that. I can live with that. The incorrect use of 'dBm' to mean 'dBmW' is a de facto industry standard - and I'm not going to try and change the world by pretending that I don't understand the incorrect 'dBm'. It depends on the industry you are in. 0dBmV is 1mV - a reasonable signal to feed to a TV set (especially directly from an antenna). 0dBm is appx 48dBmV (250mV) - and that's one hell of a TV signal! With a 75 ohm source impedance (antenna and coax) - and no significant levels of outside noise-like interference, a 0dBmV (1mV) analogue NTSC signal, direct from an antenna, will have a CNR of around 57dB. A TV set with a decent tuner noise figure (5dB?) or a set-top box (8dB) will produce essentially noise-free pictures. However, with an analogue TV signal from a large cable TV system, the signal CNR will be much worse than 57dB (regardless of its level). If I recall correctly, the NCTA ( National Cable Television Association) minimum spec is a CNR of 43dB (UK is 6B). At this ratio, it is judged that picture noise is just beginning to become visible. CNR is not important because the bandwidth does not change. You're havin' a laff - surely?! Nope. OK. Are you by any chance related to John McEnroe? http://www.youtube.com/watch?v=ekQ_Ja02gTY Not everyone works the same way. Your insistence on using CNR shows you know nothing about how the industry measures signal strength. I'm not insisting on anything. However, an analogue with a poor CNR will produce noisy pictures - regardless of the signal level. Similarly, a digital signal with a too poor an SNR/MER will fail to decode - regardless of the signal level. I think the UK cable TV spec for digital signals is 25dB (although a good set-top box will decode down to the mid-teens). External noise is somewhat consistent. Front ends are pretty much comparable in their S/N ratio. The only problems with noise are generally if you have something generating noise locally. But that is not a problem with the signal nor the receiver. That is why the real world uses signal strength to determine proper signal levels. CNR in TV is not used nor is it required when the other parameters are known. So pray tell me why, in my many years in the cable TV industry, I spent so many pointless hours measuring (among all the other parameters) CNR? Maybe because you're talking to people who design front ends, etc. They are only a small group in the entire industry. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Quad shield coax & dielectric?
On 3/17/2014 12:21 PM, Jeff wrote:
On 17/03/2014 16:01, Jerry Stuckle wrote: On 3/17/2014 11:58 AM, Jerry Stuckle wrote: Then why, pray tell, does the several $K Sencore signal analyzer sitting on the back shelf (because it's now pretty much obsolete) say "dbm"? It has been that way since I first started with MATV systems back in the early 70's. It's so common many cable techs wouldn't know there even is I can't comment onyour Sencore signal analyzer as I have never used one, BUT every other signal generator and spectrum analyser I have come across and used, from HP/Agilent, R&S, MI etc etc when labelled dBm mean dB relative to a milliwatt. Also every other RF engineer I have come across universally understands dBm to mean dB relative to a milliwatt NOT dBmV. Just check the specs of any rf test gear line you will see that they refer to dbm meaning dB relative to a milliwatt. Even Sencore's website with the specs of their latest equipment, Where they mean dBuV or dBmV they say so. Jeff Remember - these are NOT RF engineers - they are only a small subset of the entire industry. These are cable installers, TV technicians, and the like. Even the TV signal generators I used in the 70's and early 80's when I did some TV work were listed as dbm. And these guys don't look at websites to use the equipment. They are given a spec to meet and meet it. They don't know and don't care if it's dBmV or dBmW. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Quad shield coax & dielectric?
Ian Jackson wrote:
Of course, the 1MW is erp, and as the transmitting antenna gains can be considerable, the transmitter won't be putting out 1MW. But again, you've got combiner losses and feeder losses ...... The transmitters feeding the old analog 1MW ERP system were running 40kW output per vision carrier. So antenna gain minus feedline and combiner losses was 14dB. The feedline was about 300m. Not RG6, of course :-) |
Quad shield coax & dielectric?
On 3/17/2014 12:09 PM, Rob wrote:
Jerry Stuckle wrote: On 3/17/2014 10:45 AM, Rob wrote: Jerry Stuckle wrote: On 3/16/2014 11:42 AM, Ian Jackson wrote: In message , Jerry Stuckle writes HDTV requires a stronger signal than the old NTSC. It really depends on how good your old analogue NTSC was. For a noiseless picture, you would need around 43dB CNR, but pictures were still more-than-watch-able at 25dB, and the picture was often still lockable at ridiculously low CNRs (when you certainly wouldn't bother watching it). Digital signals can work at SNRs down to around 15dB for 64QAM and 20dB for 256QAM (although if it's a little below this, and you will suddenly get nothing). That has not been our experience. We had a number of customers here in the DC area who had great pictures on NTSC sets, but got either heavy pixilation or no picture at all when the switchover occurred. We sent them to a company which does tv antenna installations (we do a lot of low voltage, including tv - but not antennas). In every case, installing a better outdoor antenna solved the problem. Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. OK, you mean absolute power. Yes, they can lower the ERP - but that does not necessarily lower the power for the signal. Remember at 1MW the power was spread over 4.25 Mhz (assuming video only, of course). Digital requires much less bandwidth, so they don't need as much power to get the same effective signal. However, digital still requires a stronger signal than analog, in the bandwidth provided. You need quite a bit of noise before it becomes visible in analog. Digital, a single noise pulse can cause the loss of several bits of information. Because of the compression involved, this is more than one or two pixels. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Quad shield coax & dielectric?
This is what I love about USENET. Ask a question and sit back and watch while
the majority of respondents argue the minutia. Thanks to those who answered on-topic. Much appreciated. |
Quad shield coax & dielectric?
Jerry Stuckle wrote:
Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. OK, you mean absolute power. Yes, they can lower the ERP - but that does not necessarily lower the power for the signal. Remember at 1MW the power was spread over 4.25 Mhz (assuming video only, of course). Digital requires much less bandwidth, so they don't need as much power to get the same effective signal. However, digital still requires a stronger signal than analog, in the bandwidth provided. You need quite a bit of noise before it becomes visible in analog. Digital, a single noise pulse can cause the loss of several bits of information. Because of the compression involved, this is more than one or two pixels. I think not much of that is correct. The systems differ a bit between US and elsewhere, but over here the channel spacing of digital and analog is the same, and the bandwidth is similar (a bit more for digital if anything). Also there is no discission of "spreading", we are just discussing peak envelope ERP. You could argue that a single digital stream sending 5 programmes means that 1 programme is transmitted at 1/5 the power, but that is not what I mean. The total ERP for 1 transmitter has been lowered, and it transmits multiple programmes to boot. Digital requires less power because it requires less signal-to-noise ratio at the receiver. |
Quad shield coax & dielectric?
In message ,
Bob E. writes This is what I love about USENET. Ask a question and sit back and watch while the majority of respondents argue the minutia. Thanks to those who answered on-topic. Much appreciated. You're welcome, Bob. At least it got the buggers stirred up! Among all the smoke and dust, did your query get adequately answered? Are you going to go ahead, and suck it and see? -- Ian |
Quad shield coax & dielectric?
On 3/17/2014 3:15 PM, Rob wrote:
Jerry Stuckle wrote: Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. OK, you mean absolute power. Yes, they can lower the ERP - but that does not necessarily lower the power for the signal. Remember at 1MW the power was spread over 4.25 Mhz (assuming video only, of course). Digital requires much less bandwidth, so they don't need as much power to get the same effective signal. However, digital still requires a stronger signal than analog, in the bandwidth provided. You need quite a bit of noise before it becomes visible in analog. Digital, a single noise pulse can cause the loss of several bits of information. Because of the compression involved, this is more than one or two pixels. I think not much of that is correct. The systems differ a bit between US and elsewhere, but over here the channel spacing of digital and analog is the same, and the bandwidth is similar (a bit more for digital if anything). Also there is no discission of "spreading", we are just discussing peak envelope ERP. You could argue that a single digital stream sending 5 programmes means that 1 programme is transmitted at 1/5 the power, but that is not what I mean. The total ERP for 1 transmitter has been lowered, and it transmits multiple programmes to boot. Digital requires less power because it requires less signal-to-noise ratio at the receiver. There are major differences between Europe's PAL and the U.S.'s NTSC. But the digital signal has much LESS bandwidth than the old analog one. That was the major impetus over here to switch to digital - to free up major bandspace in the VHF and UHF spectrums. We now have as many (or, in some areas, more) stations in a much smaller band than before. Digital requires less power because the bandwidth is much lower. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Quad shield coax & dielectric?
In message , Jerry Stuckle
writes On 3/17/2014 3:15 PM, Rob wrote: Jerry Stuckle wrote: Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. OK, you mean absolute power. Yes, they can lower the ERP - but that does not necessarily lower the power for the signal. Remember at 1MW the power was spread over 4.25 Mhz (assuming video only, of course). Digital requires much less bandwidth, so they don't need as much power to get the same effective signal. However, digital still requires a stronger signal than analog, in the bandwidth provided. You need quite a bit of noise before it becomes visible in analog. Digital, a single noise pulse can cause the loss of several bits of information. Because of the compression involved, this is more than one or two pixels. I think not much of that is correct. The systems differ a bit between US and elsewhere, but over here the channel spacing of digital and analog is the same, and the bandwidth is similar (a bit more for digital if anything). Also there is no discission of "spreading", we are just discussing peak envelope ERP. You could argue that a single digital stream sending 5 programmes means that 1 programme is transmitted at 1/5 the power, but that is not what I mean. The total ERP for 1 transmitter has been lowered, and it transmits multiple programmes to boot. Digital requires less power because it requires less signal-to-noise ratio at the receiver. There are major differences between Europe's PAL and the U.S.'s NTSC. Where do you get these strange ideas? Yes, there are differences (the major one being the subcarrier phase alternation of PAL), but otherwise the systems are very similar - and none of the differences really affect the basics of RF system measurements. But the digital signal has much LESS bandwidth than the old analog one. No it doesn't. It's the same. In the UK the 8MHz wide analogue channels have been replaced with an 8MHz wide digital QAM signal, and this occupies the same channel frequency. Unless I'm very much mistaken, the US has done the same (except that the channels are 6MHz wide). That was the major impetus over here to switch to digital - to free up major bandspace in the VHF and UHF spectrums. The 'freeing-up' is because each QAM multiplexed transport stream carries typically up to 6 TV channels and 6 high-quality stereo radio channels. We now have as many (or, in some areas, more) stations in a much smaller band than before. Digital requires less power because the bandwidth is much lower. Only insofar as the digital decoder can successfully extract accurate data from the 6 or 8MHz wide multiplexed transport stream at signal-to-noise ratios which, for analogue, would produce barely watchable pictures. -- Ian |
Quad shield coax & dielectric?
On 3/17/2014 5:03 PM, Ian Jackson wrote:
In message , Jerry Stuckle writes On 3/17/2014 3:15 PM, Rob wrote: Jerry Stuckle wrote: Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. OK, you mean absolute power. Yes, they can lower the ERP - but that does not necessarily lower the power for the signal. Remember at 1MW the power was spread over 4.25 Mhz (assuming video only, of course). Digital requires much less bandwidth, so they don't need as much power to get the same effective signal. However, digital still requires a stronger signal than analog, in the bandwidth provided. You need quite a bit of noise before it becomes visible in analog. Digital, a single noise pulse can cause the loss of several bits of information. Because of the compression involved, this is more than one or two pixels. I think not much of that is correct. The systems differ a bit between US and elsewhere, but over here the channel spacing of digital and analog is the same, and the bandwidth is similar (a bit more for digital if anything). Also there is no discission of "spreading", we are just discussing peak envelope ERP. You could argue that a single digital stream sending 5 programmes means that 1 programme is transmitted at 1/5 the power, but that is not what I mean. The total ERP for 1 transmitter has been lowered, and it transmits multiple programmes to boot. Digital requires less power because it requires less signal-to-noise ratio at the receiver. There are major differences between Europe's PAL and the U.S.'s NTSC. Where do you get these strange ideas? Yes, there are differences (the major one being the subcarrier phase alternation of PAL), but otherwise the systems are very similar - and none of the differences really affect the basics of RF system measurements. From facts. But the digital signal has much LESS bandwidth than the old analog one. No it doesn't. It's the same. In the UK the 8MHz wide analogue channels have been replaced with an 8MHz wide digital QAM signal, and this occupies the same channel frequency. Unless I'm very much mistaken, the US has done the same (except that the channels are 6MHz wide). Wrong again. That was the major impetus over here to switch to digital - to free up major bandspace in the VHF and UHF spectrums. The 'freeing-up' is because each QAM multiplexed transport stream carries typically up to 6 TV channels and 6 high-quality stereo radio channels. Ah, so the channel is effectively only 1Mhz wide then. We now have as many (or, in some areas, more) stations in a much smaller band than before. Digital requires less power because the bandwidth is much lower. Only insofar as the digital decoder can successfully extract accurate data from the 6 or 8MHz wide multiplexed transport stream at signal-to-noise ratios which, for analogue, would produce barely watchable pictures. You really don't understand digital, do you? I hate it when someone tries to tell me my job which I've been doing for years... But some people just think they know it all... -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Quad shield coax & dielectric?
In message , Jerry Stuckle
writes On 3/17/2014 5:03 PM, Ian Jackson wrote: In message , Jerry Stuckle writes On 3/17/2014 3:15 PM, Rob wrote: Jerry Stuckle wrote: Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. OK, you mean absolute power. Yes, they can lower the ERP - but that does not necessarily lower the power for the signal. Remember at 1MW the power was spread over 4.25 Mhz (assuming video only, of course). Digital requires much less bandwidth, so they don't need as much power to get the same effective signal. However, digital still requires a stronger signal than analog, in the bandwidth provided. You need quite a bit of noise before it becomes visible in analog. Digital, a single noise pulse can cause the loss of several bits of information. Because of the compression involved, this is more than one or two pixels. I think not much of that is correct. The systems differ a bit between US and elsewhere, but over here the channel spacing of digital and analog is the same, and the bandwidth is similar (a bit more for digital if anything). Also there is no discission of "spreading", we are just discussing peak envelope ERP. You could argue that a single digital stream sending 5 programmes means that 1 programme is transmitted at 1/5 the power, but that is not what I mean. The total ERP for 1 transmitter has been lowered, and it transmits multiple programmes to boot. Digital requires less power because it requires less signal-to-noise ratio at the receiver. There are major differences between Europe's PAL and the U.S.'s NTSC. Where do you get these strange ideas? Yes, there are differences (the major one being the subcarrier phase alternation of PAL), but otherwise the systems are very similar - and none of the differences really affect the basics of RF system measurements. From facts. Care to share a few of your 'facts'? How do the relatively minor differences between analogue PAL and NTSC affect how you do RF (and most video) performance measurements? But the digital signal has much LESS bandwidth than the old analog one. No it doesn't. It's the same. In the UK the 8MHz wide analogue channels have been replaced with an 8MHz wide digital QAM signal, and this occupies the same channel frequency. Unless I'm very much mistaken, the US has done the same (except that the channels are 6MHz wide). Wrong again. I assure you that what I said about the UK situation is 100% correct. However, I've lost touch with what you do in the USA - so as I'm wrong, how do you transmit digital TV. In particular, how do cable TV systems organise the RF spectrum? That was the major impetus over here to switch to digital - to free up major bandspace in the VHF and UHF spectrums. The 'freeing-up' is because each QAM multiplexed transport stream carries typically up to 6 TV channels and 6 high-quality stereo radio channels. Ah, so the channel is effectively only 1Mhz wide then. No. In the UK, the 'channel' is 8MHz wide, and occupies the same frequency slot as the old single analogue channel. It is a QAM (or sometimes QPSK) multiplex of all the programmes it contains. Yes, if you have six TV channels in a 6MHz wide QAM mux you could consider that each channel occupies 1MHz, but they are not six adjacent individual digital signals. They are all jumbled up in the single 6MHz digital signal. The decoder sorts them out automagically, and puts the required picture on your TV screen. We now have as many (or, in some areas, more) stations in a much smaller band than before. Digital requires less power because the bandwidth is much lower. Only insofar as the digital decoder can successfully extract accurate data from the 6 or 8MHz wide multiplexed transport stream at signal-to-noise ratios which, for analogue, would produce barely watchable pictures. You really don't understand digital, do you? I have to admit that I used to be intimately familiar with many aspects of analogue, but there's a lot about digital that I don't know. Fortunately, these days I don't really have to! I hate it when someone tries to tell me my job which I've been doing for years... But some people just think they know it all... Se above. -- Ian |
Quad shield coax & dielectric?
Jerry Stuckle wrote:
That was the major impetus over here to switch to digital - to free up major bandspace in the VHF and UHF spectrums. The 'freeing-up' is because each QAM multiplexed transport stream carries typically up to 6 TV channels and 6 high-quality stereo radio channels. Ah, so the channel is effectively only 1Mhz wide then. That is only an "average" that you get when you divide the total bandwidth by the number of TV programmes transmitted. As multiple TV programmes are transmitted on a single channel, that occupies the width of a classical analog channel that could transmit only a single programme, more programmes can be put in the same bandwidth. However, to receive one of them you really need to receive the entire channel (several MHz wide), so all link budget calculations should be based on the full bandwidth. Later, the receiver throws away most of the bits it has received and decodes only the information for one of the TV programmes. |
Quad shield coax & dielectric?
On 17/03/2014 15:45, Jeff wrote:
I also dispute that televisions are made to handle +20dBm; that is 100mW far in excess of what a tv tuner can handle without overload!!!! +20dbmV may be but not +20dbm. Jeff I know little about TV broadcasting, but in my (audio) field, 0 dBm is taken as a level of 1 milliwatt into 600 ohms (0.775 V). Funny how all these "standards" arise! Incidentally, during the early development of 10cm radar kit, the "dB" was banished from the lab. the chaps preferring to express their results in linear units. Les. |
Quad shield coax & dielectric?
On 18/03/2014 10:10, Lordgnome wrote:
On 17/03/2014 15:45, Jeff wrote: I also dispute that televisions are made to handle +20dBm; that is 100mW far in excess of what a tv tuner can handle without overload!!!! +20dbmV may be but not +20dbm. Jeff I know little about TV broadcasting, but in my (audio) field, 0 dBm is taken as a level of 1 milliwatt into 600 ohms (0.775 V). Funny how all these "standards" arise! Indeed, 0dBm is 1 milliwatt, a measure of power, so it is 1mW into whatever your system impedance happens to be, the actual voltage (& current) will depend on your system impedance, 50, 75, 600 ohms or whatever. Jeff |
Quad shield coax & dielectric?
In message , Jeff writes
On 18/03/2014 10:10, Lordgnome wrote: On 17/03/2014 15:45, Jeff wrote: I also dispute that televisions are made to handle +20dBm; that is 100mW far in excess of what a tv tuner can handle without overload!!!! +20dbmV may be but not +20dbm. Jeff I know little about TV broadcasting, but in my (audio) field, 0 dBm is taken as a level of 1 milliwatt into 600 ohms (0.775 V). Funny how all these "standards" arise! Indeed, 0dBm is 1 milliwatt, a measure of power, so it is 1mW into whatever your system impedance happens to be, the actual voltage (& current) will depend on your system impedance, 50, 75, 600 ohms or whatever. Quite. However, it's unfortunate that the 'W' seems to have got dropped off the end - thus allowing dBm to be used carelessly and incorrectly (as Jerry seems to have been doing). -- Ian |
Quad shield coax & dielectric?
Indeed, 0dBm is 1 milliwatt, a measure of power, so it is 1mW into whatever your system impedance happens to be, the actual voltage (& current) will depend on your system impedance, 50, 75, 600 ohms or whatever. Quite. However, it's unfortunate that the 'W' seems to have got dropped off the end - thus allowing dBm to be used carelessly and incorrectly (as Jerry seems to have been doing). But it always has been so, and I don't think it is a case of the 'W' being forgotten, it was never there in the first place since the 40's when dBm started to come into use. Jeff |
Quad shield coax & dielectric?
On 3/18/2014 4:56 AM, Ian Jackson wrote:
In message , Jerry Stuckle writes On 3/17/2014 5:03 PM, Ian Jackson wrote: In message , Jerry Stuckle writes On 3/17/2014 3:15 PM, Rob wrote: Jerry Stuckle wrote: Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. OK, you mean absolute power. Yes, they can lower the ERP - but that does not necessarily lower the power for the signal. Remember at 1MW the power was spread over 4.25 Mhz (assuming video only, of course). Digital requires much less bandwidth, so they don't need as much power to get the same effective signal. However, digital still requires a stronger signal than analog, in the bandwidth provided. You need quite a bit of noise before it becomes visible in analog. Digital, a single noise pulse can cause the loss of several bits of information. Because of the compression involved, this is more than one or two pixels. I think not much of that is correct. The systems differ a bit between US and elsewhere, but over here the channel spacing of digital and analog is the same, and the bandwidth is similar (a bit more for digital if anything). Also there is no discission of "spreading", we are just discussing peak envelope ERP. You could argue that a single digital stream sending 5 programmes means that 1 programme is transmitted at 1/5 the power, but that is not what I mean. The total ERP for 1 transmitter has been lowered, and it transmits multiple programmes to boot. Digital requires less power because it requires less signal-to-noise ratio at the receiver. There are major differences between Europe's PAL and the U.S.'s NTSC. Where do you get these strange ideas? Yes, there are differences (the major one being the subcarrier phase alternation of PAL), but otherwise the systems are very similar - and none of the differences really affect the basics of RF system measurements. From facts. Care to share a few of your 'facts'? How do the relatively minor differences between analogue PAL and NTSC affect how you do RF (and most video) performance measurements? But the digital signal has much LESS bandwidth than the old analog one. No it doesn't. It's the same. In the UK the 8MHz wide analogue channels have been replaced with an 8MHz wide digital QAM signal, and this occupies the same channel frequency. Unless I'm very much mistaken, the US has done the same (except that the channels are 6MHz wide). Wrong again. I assure you that what I said about the UK situation is 100% correct. However, I've lost touch with what you do in the USA - so as I'm wrong, how do you transmit digital TV. In particular, how do cable TV systems organise the RF spectrum? That was the major impetus over here to switch to digital - to free up major bandspace in the VHF and UHF spectrums. The 'freeing-up' is because each QAM multiplexed transport stream carries typically up to 6 TV channels and 6 high-quality stereo radio channels. Ah, so the channel is effectively only 1Mhz wide then. No. In the UK, the 'channel' is 8MHz wide, and occupies the same frequency slot as the old single analogue channel. It is a QAM (or sometimes QPSK) multiplex of all the programmes it contains. Yes, if you have six TV channels in a 6MHz wide QAM mux you could consider that each channel occupies 1MHz, but they are not six adjacent individual digital signals. They are all jumbled up in the single 6MHz digital signal. The decoder sorts them out automagically, and puts the required picture on your TV screen. We now have as many (or, in some areas, more) stations in a much smaller band than before. Digital requires less power because the bandwidth is much lower. Only insofar as the digital decoder can successfully extract accurate data from the 6 or 8MHz wide multiplexed transport stream at signal-to-noise ratios which, for analogue, would produce barely watchable pictures. You really don't understand digital, do you? I have to admit that I used to be intimately familiar with many aspects of analogue, but there's a lot about digital that I don't know. Fortunately, these days I don't really have to! I hate it when someone tries to tell me my job which I've been doing for years... But some people just think they know it all... Se above. You've lost track of a lot. And I'm tired of teaching a pig to sing. You know nothing about what I do, who I work with, or what's going on in the United States. Yet you think you know more than I do about my job, the people in my industry, and the equipment I use. I tell you what. You come over and do my job for about ten years. Then, MAYBE, you'll be qualified enough to know something about it. Until then, you're just a troll. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Quad shield coax & dielectric?
On 3/18/2014 5:11 AM, Rob wrote:
Jerry Stuckle wrote: That was the major impetus over here to switch to digital - to free up major bandspace in the VHF and UHF spectrums. The 'freeing-up' is because each QAM multiplexed transport stream carries typically up to 6 TV channels and 6 high-quality stereo radio channels. Ah, so the channel is effectively only 1Mhz wide then. That is only an "average" that you get when you divide the total bandwidth by the number of TV programmes transmitted. As multiple TV programmes are transmitted on a single channel, that occupies the width of a classical analog channel that could transmit only a single programme, more programmes can be put in the same bandwidth. However, to receive one of them you really need to receive the entire channel (several MHz wide), so all link budget calculations should be based on the full bandwidth. Later, the receiver throws away most of the bits it has received and decodes only the information for one of the TV programmes. You need to check on how the signals are transmitted. You seem claim to know a lot about how U.S. TV works, even though you're thousands of miles away. But then you know a lot more about my job, the people I work with, and the tools I use than I do. Come on over and do my job for about ten years. Then maybe, just maybe, you'll be qualified to comment on it. Otherwise, I just consider you a troll. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Quad shield coax & dielectric?
In message , Jerry Stuckle
writes On 3/18/2014 4:56 AM, Ian Jackson wrote: In message , Jerry Stuckle writes On 3/17/2014 5:03 PM, Ian Jackson wrote: In message , Jerry Stuckle writes On 3/17/2014 3:15 PM, Rob wrote: Jerry Stuckle wrote: Most likely the company reduced the transmitted power by a factor of 10 at the time of the switchover, to put the added link margin in their own pockets. (transmitting a megawatt of ERP as was regular in the analog days puts a serious dent in your electricity bill, even when you have a lot of antenna gain) Not at all. If anything, they raised their power. Here they went from 1 megawatt to about 50 kilowatt (ERP). And then there are several programmes on one transponder, instead of one analog programme. This gives significant savings in power. OK, you mean absolute power. Yes, they can lower the ERP - but that does not necessarily lower the power for the signal. Remember at 1MW the power was spread over 4.25 Mhz (assuming video only, of course). Digital requires much less bandwidth, so they don't need as much power to get the same effective signal. However, digital still requires a stronger signal than analog, in the bandwidth provided. You need quite a bit of noise before it becomes visible in analog. Digital, a single noise pulse can cause the loss of several bits of information. Because of the compression involved, this is more than one or two pixels. I think not much of that is correct. The systems differ a bit between US and elsewhere, but over here the channel spacing of digital and analog is the same, and the bandwidth is similar (a bit more for digital if anything). Also there is no discission of "spreading", we are just discussing peak envelope ERP. You could argue that a single digital stream sending 5 programmes means that 1 programme is transmitted at 1/5 the power, but that is not what I mean. The total ERP for 1 transmitter has been lowered, and it transmits multiple programmes to boot. Digital requires less power because it requires less signal-to-noise ratio at the receiver. There are major differences between Europe's PAL and the U.S.'s NTSC. Where do you get these strange ideas? Yes, there are differences (the major one being the subcarrier phase alternation of PAL), but otherwise the systems are very similar - and none of the differences really affect the basics of RF system measurements. From facts. Care to share a few of your 'facts'? How do the relatively minor differences between analogue PAL and NTSC affect how you do RF (and most video) performance measurements? But the digital signal has much LESS bandwidth than the old analog one. No it doesn't. It's the same. In the UK the 8MHz wide analogue channels have been replaced with an 8MHz wide digital QAM signal, and this occupies the same channel frequency. Unless I'm very much mistaken, the US has done the same (except that the channels are 6MHz wide). Wrong again. I assure you that what I said about the UK situation is 100% correct. However, I've lost touch with what you do in the USA - so as I'm wrong, how do you transmit digital TV. In particular, how do cable TV systems organise the RF spectrum? That was the major impetus over here to switch to digital - to free up major bandspace in the VHF and UHF spectrums. The 'freeing-up' is because each QAM multiplexed transport stream carries typically up to 6 TV channels and 6 high-quality stereo radio channels. Ah, so the channel is effectively only 1Mhz wide then. No. In the UK, the 'channel' is 8MHz wide, and occupies the same frequency slot as the old single analogue channel. It is a QAM (or sometimes QPSK) multiplex of all the programmes it contains. Yes, if you have six TV channels in a 6MHz wide QAM mux you could consider that each channel occupies 1MHz, but they are not six adjacent individual digital signals. They are all jumbled up in the single 6MHz digital signal. The decoder sorts them out automagically, and puts the required picture on your TV screen. We now have as many (or, in some areas, more) stations in a much smaller band than before. Digital requires less power because the bandwidth is much lower. Only insofar as the digital decoder can successfully extract accurate data from the 6 or 8MHz wide multiplexed transport stream at signal-to-noise ratios which, for analogue, would produce barely watchable pictures. You really don't understand digital, do you? I have to admit that I used to be intimately familiar with many aspects of analogue, but there's a lot about digital that I don't know. Fortunately, these days I don't really have to! I hate it when someone tries to tell me my job which I've been doing for years... But some people just think they know it all... Se above. You've lost track of a lot. And I'm tired of teaching a pig to sing. You know nothing about what I do, who I work with, or what's going on in the United States. Yet you think you know more than I do about my job, the people in my industry, and the equipment I use. I tell you what. You come over and do my job for about ten years. Then, MAYBE, you'll be qualified enough to know something about it. Until then, you're just a troll. I don't know which thread you've been reading, but it's certainly not this one. Yes, I don't really know what you do (apart from, I believe you've said, working for a company that installs lots of cable) - but does that really matter? Regardless of what you do for a living, it hasn't prevented some of your statements and assertions being totally and outrageously incorrect. However, unlike you, I'm not going trying to prove I'm right by playing an "I've been an XXX for YY years, so I should know what I'm talking about" card (although you can have a guess, if you like). As for coming over and doing your job - thanks for the kind offer, but no thanks. I've had enough of work to last a lifetime, and I'm now well into my retirement. -- Ian |
Quad shield coax & dielectric?
Jerry Stuckle wrote:
On 3/18/2014 5:11 AM, Rob wrote: Jerry Stuckle wrote: That was the major impetus over here to switch to digital - to free up major bandspace in the VHF and UHF spectrums. The 'freeing-up' is because each QAM multiplexed transport stream carries typically up to 6 TV channels and 6 high-quality stereo radio channels. Ah, so the channel is effectively only 1Mhz wide then. That is only an "average" that you get when you divide the total bandwidth by the number of TV programmes transmitted. As multiple TV programmes are transmitted on a single channel, that occupies the width of a classical analog channel that could transmit only a single programme, more programmes can be put in the same bandwidth. However, to receive one of them you really need to receive the entire channel (several MHz wide), so all link budget calculations should be based on the full bandwidth. Later, the receiver throws away most of the bits it has received and decodes only the information for one of the TV programmes. You need to check on how the signals are transmitted. You seem claim to know a lot about how U.S. TV works, even though you're thousands of miles away. But then you know a lot more about my job, the people I work with, and the tools I use than I do. Come on over and do my job for about ten years. Then maybe, just maybe, you'll be qualified to comment on it. Otherwise, I just consider you a troll. I know that the system used in the USA is different from what it is here, but this mostly concerns the modulation method used for terrestrial transmissions. Both methods (8VSB and COFDM) have their merit, and this was discussed a lot in the past. The same-frequency network we have in operation here would not be possible with 8VSB, but in long reach operation 8VSB is claimed to be better. However, the general principle of using a full classical analog channel (8 MHz here, 6 MHz for you) in its entirety to transmit a multiplexed transport stream conveying several TV programmes is the same. SCPC systems (where a transport rate is chosen to just fit the bitrate required for a single programme, and the resulting channel bandwith is correspondingly reduced) is used on some satellites, mainly for satellite newsgathering and other ad-hoc links, and sometimes for DTH transmission from really small stations. It is not popular because it wastes bandwidth and transponder output power headroom. |
Quad shield coax & dielectric?
In article ,
Jerry Stuckle wrote: You need to check on how the signals are transmitted. You seem claim to know a lot about how U.S. TV works, even though you're thousands of miles away. But then you know a lot more about my job, the people I work with, and the tools I use than I do. Jerry, I'm intrigued by what you say here. I just skimmed through the first few parts of the ATSC standard document (ATSC A/53 parts 1-3). What I see there, indicates that there's a single MPEG-2 transport stream, carrying several interleaved elementary streams (audio and video). This transport stream is trellis-encoded, and then used to modulate a single RF carrier (VSB), with a 6 MHz channel width. With that modulation, it seems to me that receiving the OTA transmission does require demodulating the entire 6 MHz signal bandwidth to recover the transport stream. The individual program streams may of course use much less than the full effective bandwidth, after de-interleaving, but I can't see how it would be practical to demodulate and decode the VSB signal and "pull out" one individual elementary stream using only a smaller "slice" of the RF signal. What am I missing here? Is it actually possible to "receive-slice" the 8VSB signal with a narrower RF passband, and pull out a specific elementary stream successfully? Are some broadcasters actually transmitting multiple modulated carriers within their 6 MHz ATSC spectrum slice? Now, I realize that cable TV transmissions may not (and often do not) use VSB. With an OFDM modulation it would be possible in principle to "slice" the 6 MHz spectrum segment into smaller, independent sets of subcarriers carrying different programs... I don't know if any cable systems do this in practice but it does seem possible. |
Quad shield coax & dielectric?
In article Jerry Stuckle writes:
OK, you mean absolute power. Yes, they can lower the ERP - but that does not necessarily lower the power for the signal. Remember at 1MW the power was spread over 4.25 Mhz (assuming video only, of course). Digital requires much less bandwidth, so they don't need as much power to get the same effective signal. However, digital still requires a stronger signal than analog, in the bandwidth provided. You need quite a bit of noise before it becomes visible in analog. Digital, a single noise pulse can cause the loss of several bits of information. Because of the compression involved, this is more than one or two pixels. Actually, if you look with a spectrum analyzer, the digital signal has the power spread much more uniformly over the 6 MHz than analog did. Digital stations here run substantially less power than their analog versions did, and deliver much better results. The power is spread across the 6 MHz channel - the signal uses the whole thing. By contrast, analog had uneven distribution of the power across its spectrum. The digital system has levels of error correction in the signal - wiping out a few bits is unlikely to affect the demodulated result. Wiping out a big burst of them is more likely to cause a problem. Alan wa6azp |
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