6 Commands
76
GPS POSITION REPORT
-------------------
Latitude: 50° 05.430' North
Longitude: 008° 45.980' East
Velocity: 0.0 Knots
Course: 360°
Recorded at: 13/12/00 19:25:48 UTC/GMT
The
POSition
command allows the argument NMEA.
cmd:
POS NMEA
<Return>
The PTC-IIIusb in this case gives out the original NMEA compatible position string
("sentence") - exactly as it was received from the GPS receiver. NMEA compatible
strings are "understood" by various navigational programs, and can thus be almost
universally used. The NMEA compatible position string usually has the following format:
$GPRMC,212234,A,5005.432,N,00845.974,E,000.0,360.0,190201,000.1,E*7B
6.72
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-IIIusb
for the DPSK modes (PACTOR-2 ARQ and PACTOR-2 Unproto). The DPSK signal of
PACTOR-2 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
), 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-IIIusb 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.