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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