Elecraft XV Transverter Owner's Manual - Manual (Page 36)

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Local Oscillator Frequency Calibration (Optional)
The local oscillator frequency in the XV50 and XV432 transverters is
adjustable over a narrow range to provide the best frequency calibration
for both transmit and receive on the 28 MHz I.F. rig. Although the local
oscillator in XV222 is not adjustable, the firmware in an Elecraft K2 or
K3 transceiver allows you to compensate for frequency errors using the
menu commands. Once the proper compensation is entered, the K2 or K3
frequency display will show the actual transmit and receive frequencies
accurately. The same menu commands may be used to correct for small
errors in the XV50 and XV432 frequency as well. See the Revision 2 and
up K2 firmware instructions or the K3 Owner’s Manual for details. See
the next page for adjusting the XV144 Local Oscillator frequency.
The frequency adjustment range is limited and you may not be able to put
the local oscillator exactly on the desired frequency. In most cases the
local oscillator will stop oscillating when the frequency is adjusted too far.
This is most likely to happen with the XV432. If the stock crystal supplied
with your kit does not have adequate adjustment range, an optional high-
accuracy local oscillator crystal is available for the XV432 transverter.
This should not be a concern when using an Elecraft K2 or K3 for the I.F.
because any remaining frequency error can be compensated for in the K2
or K3 using the menu commands as described above.
The following procedures allow you to calibrate the local oscillator in
several ways:
 Use a counter to measure the local oscillator frequency at 22 MHz
(XV50) or 404 MHz (XV432).
 Use a counter to measure the output frequency of the transverter.
 Use a received signal produced by a calibrated signal generator,
transmitter or other known source.
Using a Counter to Measure the Local Oscillator Frequency
Turn the transverter power on and allow the transverter to stabilize
for at least 5 minutes at room temperature (approx. 20 – 25º C).
Connect a DMM set to measure DC volts between a ground point and
TP1 in the lower left quadrant of the RF PCB.
i
In the next step you will connect the frequency counter to a
circuit that has a DC voltage. If your counter does not provide
protection against DC voltages, or if you aren’t sure, place a capacitor
in series with the counter input. Any value from 100 pF to .01 µF is
suitable.
Attach the frequency counter to either end of molded inductor L3
(near T1 on the RF PCB).
Adjust the local oscillator frequency as follows:
XV50: Adjust trimmer capacitor C33 for a reading of 22.00000
MHz on the frequency counter. Make sure the voltage at TP1
remains between 0.8 and 1.2 VDC.
XV432: Adjust L4 for a reading as close as possible to 404.000
MHz on the frequency counter. Make sure the voltage at TP1
remains between 2 and 3.5 VDC.
Monitor the voltage at TP1 while switching the transverter power on
and off several times to be sure the local oscillator starts reliably.
Using a Counter to Measure the Transverter Output Frequency
Turn on power to the transverter and allow the transverter to stabilize
for at least 5 minutes at room temperature (approx. 20 – 25º C).
Attach a dummy load to the transverter output.
Connect the frequency counter to sample the RF output from the
transverter. Do NOT connect your counter directly to the antenna
output without a suitable attenuator to protect the counter input. If
you do not have a suitable attenuator, connect an insulated wire to the
counter input and position the wire near antenna relay K1 on the RF PCB.
You may need to experiment with the position of the wire to pick up
enough RF to operate the counter. Do not wrap the wire around L10 or
L11. That would detune the output filter and could damage the RF power
module.
Set the 28-MHz rig to transmit at 28.0000 MHz. If you are using an
Elecraft K2 or K3 for the I.F. and have the transverter menu enabled, set