Heathkit HD-1250 - Transmitter Adjustment; Shunt and Series Trap Adjustment; To Measure the Q of a Tuned Circuit

Page 48
TRANSMITTER
ADJUSTMENT
1. Use
the
Dip
Meter
in the injection mode.
2. Turn the transmitter on. but do not apply plate voltage.
3. Pretune all resonant circuits
to their respective frequencies.
4. Change
the Dip Meter
to
the
absorption mode.
5. Apply final voltage
to the transmitter.
6. Start with a large coupling distance as
you
search for
the
transmitter
frequency. Decrease coupling until the signal is detected on the meter or
heard in
the headphones.
7.
Peak the individual circuits of the transmitter as you use the
transmitter's
meters or the Dip Meter (in the absorption mode).
SHUNT AND
SERIES TRAP ADJUSTMENT
NOTE: Other passive filters may also be aligned if
you use
the method described
in the following steps.
1. Use the Dip Meter in the injection
mode.
2.
For
parallel traps, position the coil close
to the test circuit. Tune the Dip
Meter for
a dip
indication
on the meter; read the resonant frequency
from
the
tuning dial.
3. To
determine
the
resonant frequency of series
traps, the inductor and
capacitor must
first
be connected in parallel. Then, find the resonant
frequency as outlined in the previous step. Replace the components back
into
the
circuit in
their
original
series arrangement.
TO MEASURE THE Q OF A TUNED CIRCUIT
Refer
to Figure
3-1
for
the
following
steps.
1.
Use the Dip Meter in the injection mode.
2. Connect a high impedance input voltmeter (through an RF probe) across
the test circuit as shown
in
Figure
3-1.
Use the lowest range
of
the
voltmeter.
3. Loosely couple the Dip Meter
to
the tank
circuit. Adjust the Dip Meter for
a
maximum reading
on the voltmeter. IMPORTANT:
Do not change the
coupling during the rest of this operation.
4.
Read the Dip Meter frequency from
the
scale
whose
color corresponds
to
the color of the coil used for
this test. Record the frequency; this is F
0
.
5.
Carefully decrease
the Dip Meter
frequency
to obtain a voltmeter reading
equal
to
70.7% of the F
0
reading.
Record
this frequency
as Fj
.
6.
Carefully increase the Dip Meter frequency,
past
center frequency F
0
,
to
obtain another voltmeter reading equal to 70.7% of the peak voltage
at
F
0
.
Record this
frequency
as F
2
.