[TenTec] Setting transmit audio levels for PSK31 and RTTY

ditzian@alltel.net ditzian@alltel.net
Thu, 12 Jul 2001 07:03:16 -0400


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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