[Elecraft] Off Frequency K2

Fri Apr 18 11:19:00 2003

Thanks to John KI6WX; Rich Lentz; Steve GU3MBS; Dave K9FZJ; George W5YR; Ron
AC7AC and any others who offered the helpful suggestions for my frequency
readout problem.

With the insight provided by so many, I have been able to "fudge" the
frequency readout to within 10/20 Hz on both USB and LSB on all bands.

The way I ended up doing it is not scientific but seems to work anyway.
What I did is try setting the 4.00000 Mhz Oscillator to exactly that
frequency with my counter.  I then did CAL PLL and found that the readout
frequency was nearly 500 Hz off from the actual "tuned" frequency of the
radio.  I then tried adjusting the 4 Mhz freq. to a lower value and found
that this actually decreased the error after CAL PLL  was run again.  I then
readjusted the 4 Mhz freq to an even lower frequency, (3.999870 and found
that after CAL PLL the frequency was dead on.  I then did CAL FIL to align
the BFO and filters and voila!  The readout now shows signals on their
actual transmitted frequency and the transmitter actually transmits on that
same frequency.  How remarkable......Very un-technical and un-scientific,
but who cares as long as the end result is what you wanted.

Proves again that there is more than one way to skin a cat.  Sometimes even
the cat won't mind too much.  Hi!

Thanks again to all.

73  de N5GF  Ed   K2 #3332  On Frequency.

----- Original Message -----
From: "John, KI6WX" <[email protected]>
To: "Elecraft Mailing List" <[email protected]>
Sent: Thursday, April 17, 2003 9:44 PM
Subject: Re: [Elecraft] Off Frequency K2

> Ed;
> Over the last two years, I've become somewhat of an expert on the K2
> oscillator design.  It is possible to get your K2 to consistently read
> frequencies to within 20 Hz.  It does take a little work and care.
>
> First you need to understand the design of the K2.  The VFO tunes in steps
> that vary in size depending on frequency.  On 10 meters, these steps are
> around 10 Hz.  On 20 meters they are around 7 Hz, and on 160 meters they
are
> about 3 Hz.  The firmware picks the nearest one to the desired frequency,
so
> we have a possible error of 5 Hz.
>
> The Cal PLL function uses the 4 MHz oscillator to determine the PLL
> reference frequency.  Even if you are very good at adjusting this
frequency,
> you will still get an error of at least 5 Hz at the frequency you are
> calibrating it.
>
> The BFO frequency is tuned in step sizes that range from 20 to 35 Hz
> depending on the VFO frequency.  The CAL FIL function measures these
> frequencies, but again this will be subject to the calibration error of
the
> 4 MHz oscillator.
>
> Finally, the K2 drifts some with temperature.  If you do your CAL PLL at
one
> temperature and run it at another temperature you will get an additional
> frequency error.  If you carefully control all of these, you can get an
> accuracy of about 20 Hz.  I don't think you can do much better given that
> the K2 does not use a complex PLL as used in many other rigs.  This buys
you
> a much better dynamic range due to better oscillator performance, lower
> current consumption, and a smaller part count, but it comes at a cost in
> frequency accuracy.
>
> To calibrate a K2, you first need to adjust the 4 MHz oscillator to be
> exactly at 4 MHz.  I had tried the fifth harmonic zero beat to WWV several
> years ago and decided it didn't have enough accuracy.  I found the best
way
> to do this was to set the K2 on 10 meters and measure the VFO frequency
with
> both an internal and external counter.  The K2 must be at its internal
> operating temperature, so you either need to do this in a warm room or let
> the K2 warm-up with the top cover in place (this can take an hour to fully
> warm-up).  You can then remove the top cover and quickly adjust the 4 MHz
> oscillator.
>
> You then need to replace the K2 cover and let it again stabilize at its
> normal internal operating temperature.  At this point you can run a CAL
PLL.
>
> Finally, you need to run a CAL FIL for each filter bandwidth and mode.
You
> must adjust the CAL FIL frequency so that it will be recorded as a new
value
> even if you don't change that frequency.  This adjusts the K2 so that the
> firmware knows the exact frequency of the BFO and the VFO can correctly
> compensate for the exact BFO frequency.
>
> If you do all of these steps carefully, you can get 20 Hz frequency
accuracy
> on 10, 15, & 20 MHz WWV.  It will probably be a little worse on 10 meters.
>
> -John
>  KI6WX
>
>
> ----- Original Message -----
> From: "n5gf" <[email protected]>
> To: <[email protected]>
> Sent: Thursday, April 17, 2003 11:03 AM
> Subject: [Elecraft] Off Frequency K2
>
>
> Looking for a helpful suggestion.   My K2 #3332 WILL NOT calibrate on
> frequency.  I have run CAL FCTR, set the 4.0000 Mhz Oscillator exactly on
> 4.0000 Mhz by using a frequency counter which has been calibrated against
> WWV to a readout of 1 Hz and by attaching the probe to TP1 and adjusting
C22
> to match the K2 readout to the counter.  I have measured the 4.000 Mhz
> crystal frequency directly on Pin 14 of U6 and adjusted it with the C22
> padder to exactly 4.000 Mhz with this same calibrated frequency counter.
I
> have used an accurately calibrated receiver and zero beat the 5th harmonic
> of the 4.000 Mhz oscillator with the 20 Mhz WWV signal.
>
> After each attempt at setting the reference oscillator I have run CAL PLL
> and CAL FIL, double checked all entries for bandwidth and frequencies of
> filter setting BF1 thru BF4.
>
> I have performed each of these methods a number of times and EVERY ONE
gives
> the same results.  When tuning in a signal off the air I find that the
> frequency readout is from 50 to 100 Hz LOW both on LSB and USB.  This
means
> that a SSB signal on 3842.00 Khz LSB will actually tune in at 3842.05 Khz
> LSB and a signal on 14200.00 Khz USB will actually tune in at 14200.05 Khz
> USB on the K2 readout.
>
> I have tried to fudge this error out by simply adjusting the 4.000 Mhz
ref.
> osc. up a little and down a little, but the error remains the same after
the
> CAL functions are run.  I realize that for a CW operator, this is a
> negligible error and means nothing because it will only vary the pitch of
> the CW signal just a little on both transmit and receive, but for SSB
> operation, especially with the narrow and sharp skirted filters of the K2,
> it becomes very annoying to my ears AND to the ears of the stations on the
> other end during a roundtable ragchew where everyone must be on the same
> frequency.
>
> Of course the simple solution here is to just tune so the readout reads 50
+
> Hz away from the actual frequency being received and forget it.  But that
> just isn't right and this radio should calibrate much closer than it does.
>
> Does anyone have a suggestion......maybe something I have missed, even
> though I've now read the books so much the print is beginning to fade from
> being illuminated to much by my beady little eyes.
>
> As always, thanks in advance
>
> 73  de N5GF  Ed  K2 #3332
>
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