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

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

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

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

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

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

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

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

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

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.