Posted by
Ron D'Eau Claire-2 on
Apr 26, 2006; 12:11am
URL: http://elecraft.85.s1.nabble.com/Need-help-for-sick-K1-tp389102p389120.html
Fred, K6DGW wrote:
So ... running my K2 is like flying an F-16 or F-117A. I don't actually
"control" the aircraft or radio, I "request" the computer to control it
for me and hope it is listening?
-------------------------------
Right, Fred, but notice that's what you did with your SX-28 too! You turned
the dial to make a frequency mark line up with the indicator. That was
"requesting" a frequency. The only thing you knew for certain was that it
wasn't exact!
The same is true of the K2. The difference is that the K2 is a lot closer
than almost any analog system at any price.
When you calibrated your SX-28, you were setting it so the requested
frequency equaled the actual frequency as close as possible. But you knew
that even at the reference frequencies you use to calibrate the receiver it
wasn't exact. That's similar to the problem with the K2's inability to be
absolutely exact to the Hz in establishing the exact tuning when you run CAL
PLL even if the 4 MHz clock is exactly on so the frequency counter function
(FCTR) in the K2 is "dead on", there's still the problem of deciding exactly
what is "on frequency". In the K2 it's not a matter of reading a line on a
frequency scale but instead is a matter of how accurately the DACs can read
the tuning voltages being applied and record their value in memory.
Then when you tuned in WWV later on your SX-28, there was the issue of
deciding exactly when the frequency mark was aligned with the index. You can
get very close, there's a limit to how "exact" you can be. That's like
tuning in 10000.00 on your K2. The DACs then have to create the tuning
voltage by the data in memory for that frequency, but there's a limit to how
close they can replicate it, just as there's a limit to how close you can
reposition the dial at 10000.000 MHz.
The lines on the SX-28 dial have to have width so you can see them. There's
a limit to how exactly you can position the pointer once the receiver is
exactly tuned to the reference source, like WWV. The K2 has a tuning
resolution of 10 Hz. That's like saying the K2's 'dial markers' are 10 Hz
wide!
And, finally, even if you did get the dial set exactly on 10000.000 Hz on
your SX-28 and you had calibrated it with the same accuracy, you are still
at the mercy of any drift in the oscillator frequency since you calibrated
it! The same is true of the K2. It will change a little with temperature and
time, although those oscillators are very stable!
One thing the K2 can't match on your SX-28. Those human-friendly knobs,
especially those honkin' big hand-wheels used for the main and bandspread
tuning!! Sigh!! But then I don't need a fork lift to pick up my K2. People
who groan when they hoist an Astron 35 amp power supply never carried an
SX-28 around.
Still, if I ever come across one that I can afford...
Ron AC7AC
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