[R-390] Line Level meter

[ka9egw at britewerkz.com]

OK, so...to get a 2/3 reading at .775Vrms... let me see--
My brain hurts.
73, Brian KA9EGW
-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of 2002tii
Sent: Tuesday, August 24, 2010 5:12 PM
To: R-390 at mailman.qth.net
Subject: Re: [R-390] Line Level meter


Brian wrote:

>0dBm is 1.228Vrms

The de facto standard for audio dB measurements is 600 ohms (which is
also the 390/A output impedance), or 0 dBm = 0.775 vrms.  1.228 vrms
is +4 dBm.  +4 dBm was often used in the US as a "0 VU" reference in
the prehistoric days, and was obtained with a meter of a specific
resistance that reads 0 VU = 0 dBm when a sine wave was applied
directly to the meter, and a 3900 ohm resistor in series with the
meter (to make it a "bridging" load on the 600 ohm line).

If anyone cares, the VU meter standards are ANSI C16.5-1942 and IEC
60268-17.

Best regards,

Don




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