Vectronics VEC-101K - Manual (Page 18)

VEC-101K Owner's Manual Shortwave Converter Kit
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7. Using a blade type alignment tool or small jeweler’s screwdriver, carefully
adjust ceramic trimmer capacitor C13 until the oscillator signal is heard
sweeping through the shortwave receiver.
8. Slowly adjust the trimmer C13 so the Local Oscillator signal falls exactly on
frequency (if the BFO is on, adjust for “zero beat”).
9. Set the receiver to the highest Local Oscillator frequency to be set.
10. Activate bandswitch SW2 so the shaft returns to the fully extended position
(high frequency band).
11. Adjust ceramic trimmer capacitor C12 until the Local Oscillator signal is
head sweeping across the receiver.
12. Carefully peak C12 so the Local Oscillator frequency falls exactly on the
receiver frequency (if the BFO is on, adjust for “zero beat”).
13. This completes the Local Oscillator alignment.
Using a frequency counter: A sensitive frequency counter is needed. Make up a
small “gimmick capacitor” using two or three inches of insulated wire twisted
together. The gimmick capacitor is used to couple the Local Oscillator signal
from pin 7 of the NE602 to the counter input. RF cables must be very short to
prevent signal attenuation. If more signal amplitude is needed, use an in line
broadband RF preamplifier. Many Tektronix scopes (465) have a vertical
amplifier output which may be used to drive a counter. Use the scope vertical
amplifier to amplify the level. Note that the gimmick capacitor will load the
oscillator, and pull its frequency to some extent.
Using off-air signals: Shortwave broadcasters operate on known schedules, and
often announce their frequencies throughout the broadcast or on the hour.
Popular Communications Magazine includes a monthly guide listing shortwave
broadcast times and frequency. Adjusting the Local Oscillator trimmers to find
areas of shortwave broadcast activity will get your converter into the “ballpark”.
Use the frequency announcements to fine tune the calibration.
Using a signal generator:
1. Set the signal generator to the lowest shortwave frequency (i.e.: 3900kHz
for 75 Meters).
The generator output should be set to about 20 uV, modulation should be AM
(1000-Hz tone) at 30% modulation.