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Quad shield coax & dielectric?
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). -- Ian --- news://freenews.netfront.net/ - complaints: --- |
Quad shield coax & dielectric?
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. 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). I don't know what the current specs the techs are using now; I don't get into the field much any more. But I would be surprised if it were less than 15-20dB. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Quad shield coax & dielectric?
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. 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 |
Quad shield coax & dielectric?
In message , Jeff writes
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. 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! I'm also not sure what the figures mean. From distant memory, the NCTA minimum RF input level (for NTSC) was 0dBmV (into a TV set - it might have been a bit more for set-top boxes), and the CNR 43dB. The UK cable TV level (for PAL set-tops) was 3dBmV to 15dBmV, with no more than 3dB between the levels of adjacent channels, and when digital signals came along, these were run around 15dB below the analogues. [Note that for both the US and the UK, one of the reasons for these obviously high signal levels is because cable set-top boxes have relatively appalling noise figures compared with your modern TV set.] UK off-air transmissions were somewhat similar, with digitals being run at 10, 16 and even occasionally 20dB below the analogues. However, when all the analogues were turned off, the digitals were turned up to typically 7dB below what the analogues had been. This would suggest that digital receivers (including HD) are at least perfectly happy with 7dB less signal than analogue - and in practice, all other things being equal, digital receivers work down to much lower signal levels than would be considered satisfactory for analogue. The only obvious proviso is that while (so far) UK SD transmissions are 64QAM, HD transmissions are 256QAM, and therefore need maybe 6dB more signal (which will only be apparent where reception is marginal). -- ian --- news://freenews.netfront.net/ - complaints: --- |
Quad shield coax & dielectric?
"Jeff" wrote in message ...
The programming and distribution companies are separate, so there is no issue with receiving different programmes from different directions. (all transmitters transmit all TV programmes available on the system) This is probably the same as in the UK. With the exception of regional "opt-outs", this is true. Not really, many of the low powered relays do not carry the full set of programmes, they only carry the 3 public service multiplexes not the full set. See :http://stakeholders.ofcom.org.uk/binaries/research/tv-research/no3factsheet.pdf Jeff True, but I thought the topic was the advantage, if any, of receiving more than one high power main station. Even in the analogue days not all relays carried Channel 5, for instance. -- ;-) .. 73 de Frank Turner-Smith G3VKI - mine's a pint. .. http://turner-smith.co.uk |
Quad shield coax & dielectric?
On 3/16/2014 1:26 PM, Jeff wrote:
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. 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. HDTV, not so much. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Quad shield coax & dielectric?
In message , Jerry Stuckle
writes On 3/16/2014 1:26 PM, Jeff wrote: 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. 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. HDTV, not so much. 7dBm is an absolutely colossal signal for a TV set. Even 0dBm is an absolutely colossal signal! -- Ian --- news://freenews.netfront.net/ - complaints: --- |
Quad shield coax & dielectric?
On 3/16/2014 7:17 PM, Ian Jackson wrote:
In message , Jerry Stuckle writes On 3/16/2014 1:26 PM, Jeff wrote: 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. 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. HDTV, not so much. 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. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Quad shield coax & dielectric?
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 |
Quad shield coax & dielectric?
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 |
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