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10.1.1 General
For each band and operating frequency, the transceiver settings must match the position of the BAND switch on
the front panel of the DX-3SP, while the PLATE and LOAD knobs must be adjusted for optimum operation
which gives – in conjunction with the input drive level, the maximum output power that can be obtained for that
input power.
When the tuning is correct, this will also result in a minimum plate current, minimum plate dissipation and good
linearity.
10.1.2 Preliminary tuning
•
Turn the BAND switch to the same band setting as the transceiver.
•
Put LOAD and PLATE knobs in the initial positions given in Table 1.
•
DX-3SP must be powered ON and "Ready", with the OPR/STBY switch in OPR position.
•
Start with the transmitter at minimum power, in a "carrier" mode e.g. RTTY or CW - key down.
•
Key the transceiver ON and gradually apply power to the DX-3SP. When 0.5 to l W of drive is reached,
the EBS is activated and the plate current jumps from zero to about 0.5 A.
•
Increase the drive until there is some output power indicated. If the current plate Ip reaches about 1 A
and there is still no output indication, turn PTT off and check the connections, the band and the initial
settings.
•
As soon as there is any power indication, tune PLATE for maximum output (and minimum plate
current).
•
Apply more drive and adjust PLATE again for maximum output. Keep PTT ON for short time only
(about 10 seconds). Go gradually, in several steps. When about 1000W output is reached, adjust LOAD
for maximum output. At low and medium power Ig2 indication will be green (the screen current is
reverse, or negative). While tuning try to minimise this green indication.
•
At high power the Ig2 indication is red (normal, or positive screen current). If there is no red Ig2
indication, it is likely that LOAD needs to be turned clockwise, towards higher numbers on the dial.
While tuning, try to maximise the red Ig2 indication.
•
Apply more drive and adjust both knobs again. When screen current is too high (flashing red Ig2
indication), increase loading by turning anti-clockwise the loading knob. (LOAD towards lower numbers
on dial) until Ig2 drops almost to zero. Then adjust PLATE for maximum output power and maximum
Ig2.
At
this point, Ig2+ is the most sensitive indicator of resonance on the working frequency
. If Ig2
goes too high (e.g. starts blinking), increase the loading again, then tune PLATE.
•
Repeat the above steps, while gradually increasing the input drive power, until the overdrive indicator
just starts turning on. Now the DX-3SP is tuned for operation at full power on that particular operating
frequency.
NOTES:
1. The maximum power is obtained from a DX-3SP when:
onset of the overdrive indication
PLATE is tuned for maximum output power, maximum screen current Ig2 and minimum plate current,
Ip
Ig2 indicator shows 2 to 4 red LEDs (depending on frequency and load, sometimes Ig2 is very low, 1
LED or no indication at all).
2. The above conditions will also give the best linearity.
