On Sun, 24 Apr 2011 15:59:20 -0400, "Martin Riddle"
wrote:



"Jim Thompson" wrote
in message ...
If you surf on "fax answer tone" you find a lot of wav files that are
continuous tones.

If I call a real fax I hear that tone, BUT it seems to be strobed on
and off at about a 0.5Hz rate.

Anyone know the actual spec rate and on/off dutycycle?

Thanks!


ITU communication standards
V.27 V.29 V.17V.34 V.34bis

You can fin the specs here http://www.3amsystems.com/wireline/hmo.htm

from V.34...
10.1.2.1A
Tone A is a 2400 Hz tone transmitted by the answer modem. Transitions
between A and A, and similarly between A and
A, are 180 degree phase reversals in the 2400 Hz tone. During the
transmission of A and A, the answer modem sends a
1800 Hz guard tone without any phase reversals. Tone A is transmitted at
1 dB below the nominal transmit power while
the guard tone is transmitted at the nominal transmit power.
NOTE – The bandwidth of a tone with phase reversals should not be
constrained in a way that appreciably affects the accuracy of
round trip delay measurements.
10.1.2.2B
Tone B is a 1200 Hz tone transmitted by the call modem. Transitions
between B and B, and similarly between B and B,
are 180 degree phase reversals in the 1200 Hz tone.
NOTE – The bandwidth of a tone with phase reversals should not be
constrained in a way that appreciably affects the accuracy of
round trip delay measurements.

Cheers


Thanks, Martin! So the "click"/strobing I'm hearing is actually a
phase reversal?

...Jim Thompson
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