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

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