[RTTY] Re: AFSK/FSK etc

[Bill Turner]

On Thu, 12 Aug 2004 15:28:54 -0500, Schulz Jonathan wrote:

>Now will someone explain low and high tones to me? ;-)

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High and low tones refer to the audio tones used to generate the RTTY
output, not the actual RF frequency being transmitted.  In the US, high
tones are almost universally used:  2125 for the MARK tone, 2295 for the
SPACE tone.  In Europe, low tones are almost universal, roughly half the
frequency of the high tones.  I don't use low tones, so I'm not familiar
with the exact frequencies.

Whichever one is in use, the actual RF output should be identical.  At
the receiving end, the operator could not tell the difference.  In all
cases, the RF MARK signal should be the higher of the two.  Having MARK
and SPACE reversed at the RF frequency is known as being "upside down".

You'll notice that the audio MARK tone is the lower but the RF MARK
frequency is higher.  This reversal happens because LSB is the universal
standard when using AFSK.  The audio tones are subtracted from the RF
carrier frequency, so a smaller subtraction results in a higher output.

Hope this helps.

--
Bill, W6WRT
QSLs via LoTW