[Elecraft] RE: K2 Frequency Alignment

Sun Jul 27 09:31:04 2003

I am using that method and thus the question. =20

The two traces are right on top of each other and I can even hear and =
see
the slow (about every two seconds) zero beat, Thus the thing is within =
less
than 1 hz off. =20

BUT, even after alignment this way, running call pll, etc.  WWV at 10 =
mhz is
off by 30 hz and WWV at 20 mhz is off by 80 mhz, after a 30 minute =
warm-up
and stays there.  BOTH 10 and 20 are right on top of the harmonic and
exhibit the same zero beat.

Do you need to set the clock for something other than =
4.00000000000000000 to
compensate for software counting inaccuracies.  It appears that the =
method
is the FCTR method and making both read the same frequency.=20

Rich

-----Original Message-----
From: KEN BROWN [mailto:[email protected]]=20
Sent: Sunday, July 27, 2003 6:49 AM
To: [email protected]
Subject: K2 Frequency Alignment

I think this method is easier to comprehend and has a couple of short =
cuts
to simplify matters. N4SO n0sss4.txt
From: Steven Gibbs <[email protected]>
Date: Wed, 18 Dec 2002 14:40:52 +0000
Subject: Re: GU3MBS Calibration technique
At 15:56 17/12/02 EST, you wrote:
>I had it sent to me.  I was not on the list
>November 29.  I  maintain the text file on
>my computer.

OK Ken.  Here's an updated version in case
you may want to pass it to someone else.

73, Steve GU3MBS

Elecraft K2 Control Board 4MHz Oscillator Adjustment

by Steve Gibbs GU3MBS      [email protected]       18 Dec 02

Here are two methods of correctly setting the K2 4MHz clock frequency =
with
greater confidence than the methods suggested in the K2 manual, =
'Alignment
and Test, Part II'.  Neither method needs a 'calibrated external =
frequency
counter' or a 'calibrated short-wave or ham-band receiver'.

Method A needs a PC running the Spectrogram program, and requires that
assembly of the K2 is complete.

Method B needs an oscilloscope and a 1MHz frequency standard. It can be
performed at the 'Alignment and Test, Part II' stage, or when assembly =
of
the K2 is complete.

=3D=3D=3D=3D=3D=3D=3D=3D

METHOD A

A1.  Set the K2 to USB.  Identify and tune (approximately zero-beat the
carrier) a standard frequency (WWV) transmission on 10MHz, 15MHZ or =
20MHz.
Tune the K2 dial about 1kHz lower. On Spectrogram you should see the WWV
carrier as a tone of about 1000Hz.  Disregard any modulation tones that =
WWV
may also be transmitting.

A2.  Disconnect the antenna; you should see a weak signal somewhere on
Spectrogram - this is the 10th (or 15th, or 20th) harmonic of a 1MHz =
signal
derived by the MCU from its 4MHz clock (you will recall that a
similarly-derived 7MHz signal is used in initial 40M alignment).  You =
can
verify that you are looking at the right signal by touching the Control
Board MCU crystal X2 or its associated C22 trimmer and noting that the
frequency on the Spectrogram display changes slightly. If you don't see =
the
MCU signal you can tune the K2 dial up or down a couple of hundred Hz =
until
you locate it.

A3.  If WWV is coming through strongly there may be enough breakthrough =
to
show WWV's signal also.  Use an insulated tuning tool (sorry, but the
Elecraft tool is rather poor for this job) to adjust Control Board C22 =
so
that the two signals coincide - final proximity may show a beat which =
can be
reduced to zero.  If WWV isn't very strong you won't see its =
breakthrough
signal so you'll have to alternately connect and disconnect the antenna
until you have the two signals giving the same frequency on the =
Spectrogram
display.

A4.  Note that the exact setting of the K2 dial and the exact frequency =
on
the Spectrogram display doesn't matter.  The sidetone frequency which =
you
have set doesn't matter either. These are the important features of this
method.  If you have a KAT2 or a KAT100 you can switch to an unconnected
ANT2 instead of disconnecting your antenna.

A5.  Re-perform CAL-FIL & CAL-PLL.

A6.  SPOT the WWV carrier in CW-nor and again in CW-rev; in each case =
the K2
dial should show 10000.00kHz (or 15000.00kHz or 20000.00kHz) probably =
plus
or minus about 20Hz.

=3D=3D=3D=3D=3D=3D=3D=3D

METHOD B

If you have access to a 1MHz frequency standard, here's a way of setting =
the
K2's 4MHz Control Board oscillator with greater certainty than trying to
zero-beat with WWV.  I used an off-the-air standard derived from the
high-accuracy carrier frequency of the BBC's 198kHz LW transmission.

You will need a 4MHz bandwidth oscilloscope having a high- sensitivity =
y-amp
(5mV/div worked for me), with an independent trigger input derived from =
your
frequency standard.

B1.  Temporarily reduce the y-amp sensitivity, connect to the trigger
source, and adjust the 'scope's timebase and trigger level to stably =
display
one or two cycles of the 1MHz standard frequency.

B2.  Connect the probe's ground connection to the Control
Board ground point.  Move the 'scope probe to the vicinity of X2-C21-C22 =
on
the Control Board, but do not touch anything, just rely on loose =
capacitive
coupling.  Switch the 'scope to maximum y-sensitivity, and look for a =
trace
showing pick-up from the 4MHz clock oscillator.

B3.  Use an insulated trimming tool (sorry, but the Elecraft tool is =
rather
poor here) to carefully adjust C22 so that the scope trace is resolved =
into
a sine wave moving slowly or rapidly either to the left or to the right.
Note that four cycles occupy the same time as one cycle of the 1MHz
reference oscillator.  Careful tuning will result in a near- stationary
display when the trimming tool is removed, and the 'scope probe is =
gradually
drawn away.  This indicates very close matching of the K2's 4MHz =
oscillator
to four times the standard frequency.  (A left or right shift of 4 =
cycles in
one second means the frequencies are matched to one part in a million.
Temperature effects will degrade frequency accuracy, so it's probably =
not
worthwhile trying for better than this).

B4.  If you are still building your K2, continue with 'Alignment and =
Test,
Part II, PLL Reference Oscillator Range Test'.  Otherwise, re-perform =
CAL
FIL & CAL PLL.

--=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D_1040222=
452=3D=3D_--

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