R-64, carefully adjust R-66 and C-65 for minimum signal level. There is some
interaction so you will need to re-adjust these several times in order to get the best
signal null.
STEP-2: Move your oscilloscope probe or diode detector to pin-2 of X-4 (the junction
of X-4, C-62, and C-89), and again adjust R-66 and C-65 for the best carrier null
while in transmit mode (PTT operated).
3.
Determine and adjust the VFO frequency and tuning range:
Set your Fine Tuning potentiometer to midrange. Leave it there for the following procedure.
Since the BFO and IF sections operate on 12.96 MHz, your BITX17A VFO must tune between
18.068 – 12.960 =
5.108 MHz
and 18.168 – 12.960 =
5.208 MHz
. Set your Course Tuning
adjustment (the polyvaricon capacitor) fully to the left. Adjust the trimmer on the back of your
polyvaricon variable capacitor so that with the knob turned fully left (minimum capacitance)
your VFO is at or slightly above 5.208 MHz. Then rotate the polyvaricon fully to the right
(maximum capacitance) and verify that the VFO is now below 5.108 MHz. This insures full 17
meter band coverage.
4.
Align the front-end bandpass filter:
While listening to a signal generator or received carrier beat note, carefully adjust C14 and
C18 for maximum received signal level. There is some interaction between these 2 capacitors,
so you may need to repeak each capacitor adjustment several times to reach maximum
sensitivity. You should see two positions on these capacitors where the signal peaks. This
indicates that you are actually tuning to the maximum sensitivity point, instead of just
approaching resonance at the end of tuning range.
5.
Adjust the transmit driver bias:
Temporarily short the microphone audio input connection. Connect an ammeter capable of
measuring approximately 200 ma in series with power to the transceiver. Key the microphone
PTT and note the idling current of your transmitter. Now slowly rotate R8 clockwise until the
idling current has increased by 20 ma. Unkey the transmitter and remove the temporary short
across the microphone audio input.
NOTE: It is possible to measure the combined current flowing in Q18 and Q19 by measuring
the DC voltage across R7 with a sensitive digital voltmeter. This is a 2.2 ohm resistor, so 20
ma through this 2.2 ohm common source resistor would occur at a voltmeter reading of 0.20 X
2.2 = 0.044 volts.
6.
Adjust the transmit power amplifier bias:
Temporarily short the microphone audio input connection. Connect an ammeter capable of
measuring approximately 300 ma in series with power to the transceiver. Key the microphone
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