Really crystal clear explanation Ron, you always the right simple words
for a newby as me... ;-)
I will now live with it... anyway, when you know the small limitation,
you can anticipate and adjust manually the difference when it needs
it.... In DX, it is no so critical, because you normally don't know the
real voice pitch of the amateur, and anyway, you tune for your best.
And if you like the pitch, if you have a good OP1 correctly tuned, you
will transmit the same good signal....
But when you contact ham during a local net, it is more critical to
have proper tuning.... but anyway I now know that one...
Thanks again Ron.
73
Le 04-08-17, à 12:53, Ron D'Eau Claire a écrit :
There's a "built in" 20 or 30 Hz error in the dial readout,
Jean-François.
It is not intentional; it is an engineering trade-off in the design to
balance cost and performance.
The K2 sets the frequencies of the VFO and BFO by adjusting a voltage
on
tuning diodes. Changing the voltage changes the capacitance of the
diode and
therefore the frequency of the BFO or Local Oscillator/VFO.
When you align the K2, these voltages are set to produce the correct
frequencies. When doing the alignment, the frequency display is
acting as a
frequency counter. That's why you must place the test probe on the
correct
test point, so the display can measure and display the frequency. The
accuracy of this display is controlled by the master 4.000 MHz clock
oscillator. That's why it is important to have this oscillator set a
closely
as possible.
Once you have the BFO or VFO set, the K2 then measures the frequency,
converts it to a digital number and stores it in a digital memory. It
does
this using an "analog to digital converter" chip or DAC.
When you are using the K2 in normal operation and, for example, tune
in a
specific frequency as shown on your frequency display, the K2 looks up
the
voltage levels the oscillators need to tune to that frequency in the
digital
memory. This number is then converted to a voltage by the DAC and
supplied
to the tuning diodes.
The error occurs in the DACs. Greater accuracy in reading and
reproducing
the exact tuning voltage needed means that a bigger digital number
must be
stored in memory. Elecraft used a DAC that guarantees that your actual
frequency within 20 or 30 Hz of the indicated value, provided the
4.000 MHz
master clock in the display was calibrated very accurately when you
did the
alignment. (Note that changing the frequency of the 4.000 MHz clock
has NO
effect on the accuracy of the tuning once you've done the alignment and
stored all the tuning values).
That seems to be what you are seeing. A 20 or 30 Hz error is quite
normal.
Some ops have gotten their accuracy closer. That can happen when the
value
the DAC stores happens to be the exact value needed. It is a matter of
luck.
After calibrating your 4.000 MHz master clock, you can often run the
PLL and
BFO alignments repeatedly and sometimes find that you have no
discernable
error, but it's rare. Where most CW ops really try to get the settings
as
close as possible is in setting the BFO frequencies for the CW
filters. With
a little luck, you can often get the values so close there's no
audible jump
in the beat frequency as you switch from one filter to the next or
from CWn
to CWr.
Ron AC7AC
-----Original Message-----
Hi,
I follow carefully the new document regarding the calibration of the 4
Mhz oscillator, and I can find that after each completed tasks, I have
always a few cycle different...
Example: before doing the tuning procedure, 14.150.12 was correct
instead of 14.150.00, so 120 Hz offset...
I did the application note entirely, and after I should tune to
14.150.03 to have the correct frequency... I always have a 0.03 or 0.02
difference....
Is it a normal behavior ? Maybe I'm a little bit to clumsy about
calibrating my K2 ;-)
73
===============================================
Jean-François Ménard / VA2VYZ
Elecraft K2 #4130
[EMAIL PROTECTED]
Club d'Astronomie Amateur de Sherbrooke
Club Radio Amateur de l'Estrie
Mon site web personnel : http://homepage.mac.com/jfmenard
===============================================
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===============================================
Jean-François Ménard / VA2VYZ
[EMAIL PROTECTED]
Club d'Astronomie Amateur de Sherbrooke
Club Radio Amateur de l'Estrie
Mon site web personnel : http://homepage.mac.com/jfmenard
===============================================
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