[ICOM] 706 MK II off frequency

[C Whitaker]

de WB2CPN             2005.07.06

The frequency error when the 706 is receiving
can be measured by comparing the audio frequency
of WWV, when the receiver is in the SSB mode, with
the WWV signal from a second receiver which in the
AM mode.  The WWV telephone line, 303-499-7111 can
be used instead of a second receiver.  Unfortunately
this method only works for those of us who can pick
up a decent WWV signal.  Further down I'll tell you
how to use stations other than WWV.

If you tune the 706 to WWV, SSB mode, readout set to
1 Hz resolution, (See 706 manual Page 1 "Front Panel"
Item 5, "Tuning Step Switch" for setting 1 Hz), and
place the speaker to the left or right of you,
then get WWV on the phone, or tune in WWV AM on a
second receiver, so that you can hear it
using your other ear.  You'll be hearing two sources
of the WWV audio tone; one from the phone or AM
receiver, and one comming from the 706.  Adjust the
volume of the 706 so that the levels in both ears are
about the same.  You, the human, are the comparitor.

If you vary the 706 frequency slightly you should hear
a beat between the two audio sources.  You want to
carefully adjust the 706 so that the beat is close
to zero, and experiment with that by bracketing the
frequency on the 706 until you get a feel for where
the 706 frequency is that produces two audio tones
that are near-coherence.  I expect the 706 to be a
few Hz off WWV's frequency, so now you know what you
706 frequency error is at that WWV frequency.

That error can be interpolated to other frequencies
in that if the error at 10 MHz is 12 Hz, the error
at 20 Hz will be 24 Hz, and at 5 MHz it will be 6 Hz.

We will not go into how to adjust the 706, and we're
not going into short and long term stability, and we're
not going into phase jitter.

I'll cover how to check the 706 transmit frequency,
which should be the same as the receive frequency
unless the offset circuitry has a problem, all in
a seperate email.  You'll need a second WWV AM or
SSB receiver, a dummy load, and the 706 mod for
treansmitting outside the ham bands.  We'll try
to hetrodyne the 706 with a signal being heard on
the second receiver.

73   Clete

P.S.  Also works with my 756ProII and a few other
radios around here.