3 Installation
15
The bootloader is automatically activated as soon as the PTC-IIIusb detects an error on
loading the PACTOR firmware, or the user wishes access to the bootloader by setting the
DIP-switch to ON.
3.4.3
SPARE
Currently no function, reserved for later extensions.
3.5
Connections to the transceiver
PACTOR-2 uses Differential Phase Shift Keying (DPSK), which leads to a very narrow
bandwidth signal. In order to maintain this advantage of PACTOR-2 on the bands, correct
setting up of the transceiver is required. Overdriving of the transceiver will lead to a
greatly increased bandwidth. The optimal adjustment from the PTC-IIIusb to the radio
equipment is described in chapter
on page
The complex PACTOR-2 modulation scheme is totally different, and has nothing
whatsoever to do with simple FSK. It is therefore IMPOSSIBLE to use the FSK
modulators found in some transceivers to generate the signal. The PACTOR-2
signal must always go via the indirect route, by using SSB to generate the HF signal.
This is of no disadvantage providing the transceiver is not overdriven.
Some hints to adjust the settings of your transmitter:
•
If possible use a 500 Hz IF-filter. Never use a IF-filter with a smaller bandwidth than
500 Hz! IF filter (SSB-filter) with wider bandwidths won´t cause problems at all.
Although the filtering by the DSP of the PTC-IIIusb is always optimized, it is
desirable to prevent noise from the input of the PTC-IIIusb as far as possible.
•
Under no circumstances use audio processors. The speech-compressor of the
transceiver will damage the PACTOR-2 signal in the same way as external DSP audio
filters being so popular at the moment. These external DSP audio filters create
unpredictable signal propagation delays which are absolutely undesirable. The PTC-
IIIusb filters the signal optimal with the integrated DSP and needs no “external help”.
•
Noise blanker and notch filter should be switched off.
The PTC is connected to the transceiver via an 8 PIN DIN socket.
PIN 1:
Audio output from the PTC to the transmitter.
The PTC-IIIusb supplies a pure
audio signal to the microphone input of the transceiver. The output amplitude can
be adjusted with the
FSKA
and
PSKA
commands from 30 to 3000 mV (peak to
peak) open circuit. The output impedance of the PTC-IIIusb is 1 k
Ω
.
PIN 2:
Ground (GND).
Collective grounding point for all signals.
PIN 3:
PTT output.
While transmission this output from the PTC-IIIusb is grounded, so
that virtually all modern transceivers are suitable. A VMOS-field-effect transistor
is used as the switch, which gives optimum results. The switched current should
not exceed 1 A.
PIN 4:
Audio from the receiver to the PTC-IIIusb.
The PTC-IIIusb gets its information
directly from the loudspeaker output of the receiver. The volume should not be
turned up too far. A
fairly low
volume is quite sufficient. It is better to take the AF
signal from a low level output which is independent of the volume control. These