In message , Jerry Stuckle
writes
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.

The TV signal levels quoted for analogue cable TV don't really involve
bandwidth. The level is always the 'RMS during sync' (or 'RMS during
peak'), which is the RMS level of the vision RF envelope during the
horizontal (or vertical) sync period. This has the advantage of
remaining constant regardless of the video content (ie it's the same for
a completely black picture or a completely white picture).. The only
requirement is that the measuring instrument has sufficient bandwidth to
embrace enough of the low frequency sideband content of the video signal
to give a reading which IS independent of the video content. On a
spectrum analyser, 300kHz resolution will display the demodulated RF
waveform (thus enabling you to read the RF level), but IIRC many field
strength meters have an IF bandwidth of typically 30kHz. However,
regardless of the actual measuring bandwidth, noise levels are
normalised to a bandwidth of 4.2MHz (NTSC) and 5.2MHz (PAL). and
signal-to-noise measurements are adjusted accordingly.

Note that the cable TV industry generally uses units of dBmV (dB with
respect to 1mV - traditionally considered a 'good' level to feed to a TV
set). This is because most of the levels the cable TV guys work with are
generally in excess of 0dBmV (typically 0 to 60dBmV).

The off-air TV guys often use dBuV (dB wrt 1microvolt), as they are
usually dealing with weaker signals. As a result, cable TV guys are
always having to mentally deduct 60dB.

RF communications guys (and domestic satellite) tend to use dBm (which
is a slovenly version of 'dBmW' - dB wrt 1mW) - despite the fact that a
lot of their levels are large negative numbers. Also note that dBm tends
to imply a Zo of 50 ohms, and dBmV/dBuV 75 ohms - but it ain't always
necessarily so.

Anyone working in the RF industry would be well advised to ensure that
they always use the correct units - for example, don't say 'dB' or 'dBm'
when you really mean dBmV. Failure to do so can often result in people
needlessly arguing and talking at cross-purposes.
--
Ian

--- news://freenews.netfront.net/ - complaints: ---

"Ian Jackson" wrote in message
...
In message , Jerry Stuckle
writes
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.

The TV signal levels quoted for analogue cable TV don't really involve
bandwidth. The level is always the 'RMS during sync' (or 'RMS during
peak'), which is the RMS level of the vision RF envelope during the
horizontal (or vertical) sync period. This has the advantage of remaining
constant regardless of the video content (ie it's the same for a
completely black picture or a completely white picture).. The only
requirement is that the measuring instrument has sufficient bandwidth to
embrace enough of the low frequency sideband content of the video signal
to give a reading which IS independent of the video content. On a spectrum
analyser, 300kHz resolution will display the demodulated RF waveform (thus
enabling you to read the RF level), but IIRC many field strength meters
have an IF bandwidth of typically 30kHz. However, regardless of the actual
measuring bandwidth, noise levels are normalised to a bandwidth of 4.2MHz
(NTSC) and 5.2MHz (PAL). and signal-to-noise measurements are adjusted
accordingly.

Note that the cable TV industry generally uses units of dBmV (dB with
respect to 1mV - traditionally considered a 'good' level to feed to a TV
set). This is because most of the levels the cable TV guys work with are
generally in excess of 0dBmV (typically 0 to 60dBmV).

The off-air TV guys often use dBuV (dB wrt 1microvolt), as they are
usually dealing with weaker signals. As a result, cable TV guys are always
having to mentally deduct 60dB.

RF communications guys (and domestic satellite) tend to use dBm (which is
a slovenly version of 'dBmW' - dB wrt 1mW) - despite the fact that a lot
of their levels are large negative numbers. Also note that dBm tends to
imply a Zo of 50 ohms, and dBmV/dBuV 75 ohms - but it ain't always
necessarily so.

Anyone working in the RF industry would be well advised to ensure that
they always use the correct units - for example, don't say 'dB' or 'dBm'
when you really mean dBmV. Failure to do so can often result in people
needlessly arguing and talking at cross-purposes.

Back in the 1970s I was involved with the assessment of the coverage of
analogue UHF TV. At that time the service limit was defined as 70dB rel
1uV/m field strength. (3.16mV/m).
At 600MHz a half wave dipole is near enough 25cm and so would capture about
a quarter of this voltage.
A typical outdoor TV antenna of the time had a gain of at least 6dB, so the
available signal level before feeder loss would be in the order of 1 - 2mV.
HTH
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk

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.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On 3/17/2014 8:27 AM, FranK Turner-Smith G3VKI wrote:
"Ian Jackson" wrote in message
...
In message , Jerry Stuckle
writes
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.

The TV signal levels quoted for analogue cable TV don't really involve
bandwidth. The level is always the 'RMS during sync' (or 'RMS during
peak'), which is the RMS level of the vision RF envelope during the
horizontal (or vertical) sync period. This has the advantage of
remaining constant regardless of the video content (ie it's the same
for a completely black picture or a completely white picture).. The
only requirement is that the measuring instrument has sufficient
bandwidth to embrace enough of the low frequency sideband content of
the video signal to give a reading which IS independent of the video
content. On a spectrum analyser, 300kHz resolution will display the
demodulated RF waveform (thus enabling you to read the RF level), but
IIRC many field strength meters have an IF bandwidth of typically
30kHz. However, regardless of the actual measuring bandwidth, noise
levels are normalised to a bandwidth of 4.2MHz (NTSC) and 5.2MHz
(PAL). and signal-to-noise measurements are adjusted accordingly.

Note that the cable TV industry generally uses units of dBmV (dB with
respect to 1mV - traditionally considered a 'good' level to feed to a
TV set). This is because most of the levels the cable TV guys work
with are generally in excess of 0dBmV (typically 0 to 60dBmV).

The off-air TV guys often use dBuV (dB wrt 1microvolt), as they are
usually dealing with weaker signals. As a result, cable TV guys are
always having to mentally deduct 60dB.

RF communications guys (and domestic satellite) tend to use dBm (which
is a slovenly version of 'dBmW' - dB wrt 1mW) - despite the fact that
a lot of their levels are large negative numbers. Also note that dBm
tends to imply a Zo of 50 ohms, and dBmV/dBuV 75 ohms - but it ain't
always necessarily so.

Anyone working in the RF industry would be well advised to ensure that
they always use the correct units - for example, don't say 'dB' or
'dBm' when you really mean dBmV. Failure to do so can often result in
people needlessly arguing and talking at cross-purposes.

Back in the 1970s I was involved with the assessment of the coverage of
analogue UHF TV. At that time the service limit was defined as 70dB rel
1uV/m field strength. (3.16mV/m).
At 600MHz a half wave dipole is near enough 25cm and so would capture
about a quarter of this voltage.
A typical outdoor TV antenna of the time had a gain of at least 6dB, so
the available signal level before feeder loss would be in the order of 1
- 2mV.
HTH

Obviously it was not the U.S. industry you were advising...

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

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.

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.



--
==================
Remove the "x" from my email address
Jerry Stuckle

==================

"Jerry Stuckle" wrote in message
...
On 3/17/2014 8:27 AM, FranK Turner-Smith G3VKI wrote:
"Ian Jackson" wrote in message
...
In message , Jerry Stuckle
writes
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.

The TV signal levels quoted for analogue cable TV don't really involve
bandwidth. The level is always the 'RMS during sync' (or 'RMS during
peak'), which is the RMS level of the vision RF envelope during the
horizontal (or vertical) sync period. This has the advantage of
remaining constant regardless of the video content (ie it's the same
for a completely black picture or a completely white picture).. The
only requirement is that the measuring instrument has sufficient
bandwidth to embrace enough of the low frequency sideband content of
the video signal to give a reading which IS independent of the video
content. On a spectrum analyser, 300kHz resolution will display the
demodulated RF waveform (thus enabling you to read the RF level), but
IIRC many field strength meters have an IF bandwidth of typically
30kHz. However, regardless of the actual measuring bandwidth, noise
levels are normalised to a bandwidth of 4.2MHz (NTSC) and 5.2MHz
(PAL). and signal-to-noise measurements are adjusted accordingly.

Note that the cable TV industry generally uses units of dBmV (dB with
respect to 1mV - traditionally considered a 'good' level to feed to a
TV set). This is because most of the levels the cable TV guys work
with are generally in excess of 0dBmV (typically 0 to 60dBmV).

The off-air TV guys often use dBuV (dB wrt 1microvolt), as they are
usually dealing with weaker signals. As a result, cable TV guys are
always having to mentally deduct 60dB.

RF communications guys (and domestic satellite) tend to use dBm (which
is a slovenly version of 'dBmW' - dB wrt 1mW) - despite the fact that
a lot of their levels are large negative numbers. Also note that dBm
tends to imply a Zo of 50 ohms, and dBmV/dBuV 75 ohms - but it ain't
always necessarily so.

Anyone working in the RF industry would be well advised to ensure that
they always use the correct units - for example, don't say 'dB' or
'dBm' when you really mean dBmV. Failure to do so can often result in
people needlessly arguing and talking at cross-purposes.

Back in the 1970s I was involved with the assessment of the coverage of
analogue UHF TV. At that time the service limit was defined as 70dB rel
1uV/m field strength. (3.16mV/m).
At 600MHz a half wave dipole is near enough 25cm and so would capture
about a quarter of this voltage.
A typical outdoor TV antenna of the time had a gain of at least 6dB, so
the available signal level before feeder loss would be in the order of 1
- 2mV.
HTH

Obviously it was not the U.S. industry you were advising...

BBC UK
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk

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)

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.

--
==================
Remove the "x" from my email address
Jerry Stuckle

==================

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.

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?!

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).
--
Ian

--- news://freenews.netfront.net/ - complaints: ---

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.

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.]




--
Ian

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