Radio Cable Type 23
NUE-PSK Digital Modem
Radio Cable Type 23
Page 25
Elecraft “KX3”
Transmitter Settings Guidance for Digital Mode Operation
Since PSK signals generated by the modem contain simultaneous multiple frequencies (over a very narrow bandwidth), it is imperative that the audio output from the modem not overdrive the input to the rig, or very poor signal quality will result. To facilitate
setting the audio drive to the rig, a potentiometer on the modem may be used to adjust the level. In addition, the modem includes provision for “measuring” the position of the potentiometer, so that it can be easily reset to the same setting in the future.
More on this later.
Press F8 on the keyboard to place the modem in the TUNE state, which is denoted by “TUNE” at the top left of the display. The modem is now generating a continuous tone, which is fed to the audio input of the rig. The PTT signal from the modem should
also cause the transceiver to switch to Transmit. At this point, the potentiometer on the modem (just to the right of the display) can be adjusted to set the power level of the transceiver. A transmit power of 15 to 40 per cent of the rig’s rated power is
recommended. (i.e. 1.6 watts with a 4 watt PSK-xx rig). Keeping the power at this level does two things. First, it minimizes distortion due to clipping. Second, it avoids excessive heating in the rig finals, since PSK is a 100% duty cycle mode. A power
meter is very handy for making this setting. Once the potentiometer has been set, press F8 again to return to receive mode. You should now be ready for transmitting PSK.
Determining Signal Quality -- If you have an additional receiver, you could use Digipan on it to view the waterfall and get an IMD reading on your modem-generated signal. (Use an attenuator or disconnected the receive antenna to ensure that you are not
overloading the receiver.) A reading below -25dB indicates a good setup of the modem and transmitter. You might try adjusting for great power output in step 3 above if you can verify that the signal has an IMD reading of least -20dB and set up to monitor
the quality of the BPSK signal, you should not try to go much higher than 3 to 4 watts in TUNE. It might be possible to run higher power, say up to 4 watts in the TUNE set above, but only if you can verify an IMD of -20dB or less.
KX3
The actual operating frequency of the modem+PSKxx rig is just the sum or difference of the center frequency of the PSX-xx rig and the audio frequency shown on the spectrum display of the modem. For example, for a PSK-40 used with a modem spectrum
display indicating 1000 Hz, the actual RF frequency being used is 14.071 – 1000 Hz = 14.070. (It would be an addition on a PSK-20 since upper sideband is used.)
1/8” stereo phono plug:
Mouser p/n:
171-6435-EX
End view
of connector pins
7 Audio IN
GND 6
8 PTT
3
Audio 4
OUT
Mic
Phones
NUE-PSK Digital Modem
Tip: Data In
Ring 1: PTT
Rng 2: Logic Gnd
Sleeve: Gnd
Data In
PTT
Gnd
5
Data Out
1
+V
2
8-pin mini-DIN
Cable Wire Colors
Digital Modem
Modem End
Pin 8 (PTT)
Pin 7 (Audio In)
Pin 6 (Ground)
Pin 4 (Audio Out)
Pin 1 (+V)
Type A
Type B
Cable or Cable
Radio End
PTT …………… blue ………... black
Data Out ……… violet ………. violet
Ground ……….. black ………. blue
Data In ………… yellow ……….yellow
+V (caution) ….. red ………….brown
1/8” stereo phono plug:
Digi-Key p/n:
CP-35401SP-ND
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