On Mon, 15 Oct 2012 01:30:08 Roger (K8RI)" <k8ri@rogerhalstead.com> :
My 897D is showing it's off frequency by 2KHz on two FM. IE the display
reads 147.002 for it to be on frequency for both transmit and receive.
Is there a way to correct the readout?
This is a common complaint, though usually on SSB,where it is more
obvious. At a specified 4 PPM after warmup, , the 8X7 family can be as
much as 588 Hz off and still be in spec at 147 MHz. You can adjust
TC5001 on the reference oscillator board to bring it into spec if it is
not.
This is best done using a frequency counter per the Yaesu manual (from
the FCC Web site):
Local Oscillator Adjustment
Reference Frequency Adjustment
a. Connect a frequency counter to TP1032.
b. Adjust the trimmer capacitor (TC5001) for 67.875000MHz ±5Hz on the
frequency counter.
c. Connect a RF millivoltmeter or an oscilloscope to the J5002 2pin
(TP1032) and confirm that
the output level is at least 70mVrms or 200mVp-p.
Done properly. the above requires a counter accurate to about .73 PPM.
Step C may not be needed.
Alternatively, if you can inject a 1 KHz (to make it easier) into the
data jack -- or couple it to the microphone from a speaker or headset,
you can adjust TC5001 by measuring the transmit output with a counter.
The adjustment will touchy.
Set the radio for 147 MHz upper sideband mode. If using the rear panel
data jack, be internal menu "38 DIG MODE" is set for User-U.
Use only enough tone input to produce the output needed to drive the
counter; do NOT connect it directly to the output connector, but couple
a small amount of RF to the counter; there are number of ways. This can
sometimes be done by using a tap made out of a coaxial T connector with
the center pin removed from the common side, and adaptors as needed. A
sensitive enough counter may only need a coupling wire or loop placed
near the coax from the rig to a dummy load, but you may need more RF to
use this method.
With 1 KHz going into a rig set for 147 MHz USB, you SHOULD see an
output on 147.001 MHz
Adjust TC5001 to achieve that.
Accurate calibration if done in a cal lab would require four times the
accuracy asked asked of teh radio. If we want to be within 20 Hz, for
example, we'd need to measure 147 MHz to within 5 Hz Hz. That is quite
difficult. How close do you want to get?
Cortland
KA5S
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