Here is some guidance for setting audio levels for the digital
modes. The procedure was given to me by G3NPA, a pretty savvy
technical guy, who got it from et al. It appears to work well. You
get a second chance to check by working someone with Zakanaka
and giving them five seconds of idle so they can read your IMD
level.
Remember also that the proper setting varies over your transmit
passband. That is, if you are using DigiPan or Zakanaka or one of
those programs that allow you to click on someone and transmit a
low or high audio tone to be zero beat, the settings will change
depending on what audio tones you are transmitting. Is there a
cure for this? Use Zakanaka and the $align$ macro, and you will
always transmit the same audio tones. Of course, you must have
a radio that can be computer controlled. The other cure is not to
use the click-anywhere feature, but to tune signals in manually so
they are in the high-tone (lower distortion) area of your transmit
passband.
FWIW, I copied the following section from the Zakanaka Help file.
*****
To adjust for RTTY or PSK audio out, do the following. For RTTY,
use a PSK signal, follow the procedure, and forget about the
readings in RTTY mode: the rig/computer settings are correct if
they are correct for PSK. Please note the need to use AVERAGE
mode on your wattmeter. This is what most built-in wattmeters
use.
Here is a procedure to check the quality of our PSK31 signal. If
we generate a clean PSK31 signal, this is pretty good evidence
that we will generate a clean RTTY signal from the same computer,
transmitter, interface hardware, and software settings.
Please note the term averaging (or RMS) RF power meter. This is
extremely important. A peak-reading meter will not show the
expected results, it will show high power at all times.
· Transmit a single tone (we use the Tune mode of Zakanaka in
PSK31 mode to do this).
Measure the output of the radio on an averaging RF power
meter. This can be an external meter in average mode or it can be
the meter built into most modern radios, as long as this is an
averaging meter. Many radios use a peak-reading meter, and this
is not what we want here. Even an older external SWR bridge can
be used, just use the forward position to get a relative reading.
Note the reading.
· Now switch from Tune to the PSK31 idle tone (BPSK mode of
Zakanaka, no typing) and note the reading again. The average
(RMS) power reading should go down to half or less than half the
power of the original average power reading.
73,
Jan Ditzian
KX2A
kx2a@arrl.net
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