SCS PTC-IIex, Руководство пользователя

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6 Commands
6.73 PSKAmpl
Default setting: 140
Parameter: X 30... 3000, AF output voltage (peak to peak) in millivolts.
This command serves to set the AF output voltage (transmitted signal) of the PTC-IIex
for the DPSK modes (PACTOR-II ARQ and PACTOR-II Unproto). The DPSK signal of
PACTOR-II has a variable envelope, the average power of which is approximately half
the peak power. It is therefore necessary to be able to adjust the PSK signal amplitude
separately from the FSK amplitude (refer also
FSKAmpl
command, chapter 6.42 , page
55 ), in order that both forms of modulation should have the correct average power level.
(A simple automatic adjustment of the PSK amplitude by a factor 1.45 does not give a
satisfactory result, as the ALC control characteristics are different from transmitter to
transmitter).
The input sensitivity of most transceivers is adjusted for the output level of an average
dynamic microphone. With 200 mV (peak to peak) therefore, most transmitters would be
fully driven with the microphone control only slightly open. It is not recommended to use
a very high
PSKAmpl
value, and then turn the MIC gain control right down, as the first
AF stage is normally Before the gain control, and rather sensitive to overdriving. We
recommend that the
PSKAmpl
value of 140 (the default setting) be left alone, and the
PSK output to be increased with the microphone gain control (if available). The
transceiver should be connected either to a 'dummy load' of appropriate power handling
capacity, or a well matched antenna. (Please pay particular attention that the chosen
frequency is really free. PTC-IIex links operate even when the signals are so weak as to
be virtually 'non existent'!). Use
U
3 <Return>to start the Unproto mode 3 (100 Bd
DBPSK). Now, using the Mic gain control of the transceiver, the power is increased until
the ALC voltage has reached the desired value.
Do not in any circumstances overdrive the transmitter, otherwise the signal will be
made considerably wider due to intermodulation products!
When correctly adjusted, the peak power should be approximately the same as the PEP
rated power output of the TRX. The effective average power is then approximately half
the maximum power, so that continuous operation should pose no thermal problems. Note
that many modern transmitters only show the peak power and this must then be taken into
consideration. If the Mic gain control must be turned up over half way, then it is
recommended the
PSKAmpl
value be increased. (By for example ‘<Esc>
PSKA
200
<Return> ‘). If there is no Mic gain adjustment available, then naturally the PSK
amplitude must be adjusted with the
PSKAmpl
command alone. The internal resistance
of the AF output level of the PTC-IIex is 330 ohm and real.
6.74 PSKTerm
Starts the PSK31 operation of the PTC-IIex. For further information refer to chapter 11 ,
page 152 .
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