Re: {Collins} SSB tuning question

I appreciate all of the advice that the members have sent to me.  I felt
foolish asking about the procedure for calibrating the frequency and
actually meant aligning the crystal calibrator.  I guess that I was
following the correct procedure, but expected to be closer to actual
frequency that I was tuning.

I have printed out your emailed response below and will add it to my files.

Best to all.


Jeff, K1YLV

-----Original Message-----
From: Glen Zook [mailto:gzook@xxxxxxxxx] 
Sent: Thursday, July 28, 2011 1:01 PM
To: 'Jerry O. Stern'; collins@xxxxxxxxxxxxx; 'Grayson Evans'; Jeff Wayne
Subject: RE: {Collins} SSB tuning question

It is definitely best to calibrate the crystal calibrator in the AM mode.
As you get closer and closer to the actual zero-beat (when the tone from WWV
is not present) you will notice that the "S" meter starts to vibrate.  The
closer and closer you get to the actual frequency this vibration will become
slower and slower.  This vibration is actually the same as the difference
between the calibrator signal and WWV.  When you reach the point that the
"S" meter reading goes very slowly from side to side you can be assured that
the calibrator is within a couple of Hertz at the 15 MHz point.

Then, tune the receiver to the desired band.  Select USB or LSB as
appropriate.  Turn on the calibrator and tune the receiver for zero-beat at
a 100 kHz point.  Then move the fiducial to indicate the correct frequency.

Even when brand new, the 70K-2 PTO in the S-Line is not absolutely linear.
Collins specifications are within 1 kHz anywhere across the band and the
vast majority are considerably closer.  My 75S-3A is "right on" at the 0,
100, and 200 kHz marks.  However, it varies in between up to around 350 Hz.
For most operation, this is plenty close.  However, especially when working
DX "split" on 40-meters, when a DX station calls out a specific frequency,
you often have to be within 20 or 30 Hz to work them.  Because of that, I
added one of the AADE digital readouts.  I use my 75S-3A to control my 32S-2
and a separate 75S-1 to listen to the DX.

Even the "latest and greatest" equipment can vary in the dial reading versus
the actual frequency.  This is because there is a master oscillator in the
unit which controls the frequency.  This oscillator can, and often does,
drift from the actual frequency and the actual frequency of the unit can be
a kHz, or more, from the actual frequency.  This oscillator needs to be
calibrated with WWV on a regular basis to insure the frequency accuracy of
the unit.

I have listened to stations arguing just who is "on frequency" and the
readings that they give out are different from each other.  At the same
time, I have used a service monitor, very closely aligned with WWV, to check
the frequency and none of the stations are within 200 or 300 kHz of the
actual frequency!  Some are even further off.

To sum it all up, if you are within 1 kHz of the "actual" frequency of the
net (and that frequency can vary), you don't sweat it!  The unit is
performing well within the original specifications.

By the way, if you replace the 15 MHz crystal with one for 10 MHz (13.155
MHz crystal frequency) you get not only a more reliable WWV frequency (10
MHz) but you also get 30-meter band coverage.

Glen, K9STH


--- On Thu, 7/28/11, Jeff Wayne <wayne4@xxxxxxxx> wrote:

I did not do a good job of describing the process.  I thoroughly warmed up
the equipment and then aligned the crystal calibrator for what I thought was
the center of 15 Mc.  I then went to the closest 100 kc division on the dial
and set the fiducial so that I was right one the zero beat of the calibrator
at the 100 kc mark.
The problem occurred when I then went to tune in some nets, including CCA
and was low on the readout each time.
My concern is that when tuning to WWV and aligning the calibrator, should I
be in the AM or USB mode when attempting to zero beat?  I do the alignment
in AM mode.  If it is done in the AM mode, is there an offset when switching
to USB and attempting to zero beat?

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