[Elecraft] Off Frequency K2
George, W5YR
[email protected]
Thu Apr 17 15:34:01 2003
Ed, I am afraid that you won't like my answer, but my experience, that of
other K2 owners I know, and Elecraft documentation all suggest that if you
can get your dial calibration within +/- 20 Hz that is about the theoretical
best you can expect. More typically, you can expect 40-50 Hz difference and
above 17 meters even more than that. And it will vary from band to band,
becoming worse the higher in frequency you go.
The K2 is a great little rig but it just does not have (a) super accurate or
consistent dial accuracy from band to band and (b) narrow, sharp-skirted IF
filters; at least none that I have measured the response spectra on.
I think that most of us just ignore the frequency deficiencies and go about
our business with working other stations. On sideband roundtables, the
important thing is to be on "a" dial frequency that the others hear you well
and you hear them properly. What the dial actually reads doesn't affect
that - but it is a pain in the neck!
Exact frequency readout is a joy - my Icom 756 PRO and PRO2 both read out to
within 2 Hz or less of WWV on every band. But, for the type of operating
that the K2 shines at, being off 50 Hz or so really isn't that big a deal.
Another point that might interest you is that the 4 MHz oscillator is not
the same as the reference oscillator that we find in more complex PLL/VCO
rigs. The only time the frequency is critical is during CAL PLL. After that
it can have any reasonably close value without affecting dial accuracy. And
changing it, as you found out, really doesn't remove the basic inaccuracy -
just shifts it around a little.
The fundamental limit to dial accuracy in the K2 is the AD converter and the
manner in which the tuning steps for the PLL are derived and stored during
CAL PLL. There are only about 3000 usable data points available for
linearization of the VFO out of the 4096 theoretically available from the
12-bit AD converter. Check back in the archives for a couple of postings
that Wayne has made that really go into detail on how the system operates.
The system works in steps of 5 KHz if I recall correctly and you have only
about 3000 points defined within the range of 5000 Hz. The spacing between
them just doesn't come out exactly even and so the values fed to control the
VCO vary from one frequency to the next and result in the dial frequency
variations you are finding.
Sorry if this is not what you wanted to hear, and I may well be missing the
point that there is, in fact, something wrong with your K2, but many of us
have spent hours trying to get the dial "on the money." The frustrating
part is that sometimes you *do* get it within a few Hz on one band and then
find that it is 60 Hz off on another. Perhaps a phone call to Elecraft might
give you some new things to try . . .
73/72, George K2 #489
Amateur Radio W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"
<mailto:[email protected]>
----- Original Message -----
From: "n5gf" <[email protected]>
To: <[email protected]>
Sent: Thursday, April 17, 2003 1:03 PM
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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