[Elecraft] K2 vs. K1 - Info please.

[Ron D'Eau Claire]

Keith KD1E asked:

1.  How do the IF filters in the K2 compare to the audio filters in the K1.
I assume they provide more selectivity and greater stop-band rejection.  I
also assume the multiple IF stage filters in my Omni will provide even
greater selectivity.
 
2.  How does the RX noise level compare between the K2 and K1.  My K1 is a
quieter rig than the more complex Omni V that it sits on.  It is just nicer
to listen to.  If the K2 is similar to the K1 it would be a very sweet rig.
 
3.  AGC - Does the K2 have multiple AGC rates (fast & slow?)?
 
4.  Tuning rates.  K1 tunes very quickly.  Similar to analog rigs from the
80's.  I assume the K2 tunes slower, yes?
 
5.  Knob wobbliness.  The knobs on my K1 are just a bit wobbly.  The pots
are tight on the PCB but the shafts have some play.  Is this the case with
the K2?  I assume it uses the same pots and has the same feel.
 
6.  SWR protection of the finals.  Are the finals SWR protected in some way?

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Keith, I don't own a K1 so I can't speak to the K1-specific issues. 

The K2 is a completely different rig from the K1, mechanically and
electrically. 

Regarding the AGC, the K1 uses audio-derived AGC while the K2 has an
I.F.-derived AGC. The I.F.-derived AGC is inherently faster to take hold
than audio AGC, producing smoother action on the "attack". That's a basic
limitation of any audio-derived AGC. It takes several cycles of rectified
signal to build up the voltage needed to control the gain. Several cycles of
signal happen much, much more quickly at the intermediate frequency than
they do at an audio frequency, so the control voltage is available much more
quickly in an I.F-derived system.

Yes, the K2's AGC has a fast and slow mode. And it has an "off" mode, which
I use a lot when tuning around<G>. Although I will say that for this
"AGC-hater" I find the K2's AGC no problem at all. I often turn AGC off
because I don't want the receiver turning up the gain between signals. I
prefer to hear the background stay constant as I tune with the signals
standing out above it at various levels  according to their strengths,
rather than having everything adjusted to about the same sound level. If I
want to dig for a weak signal down near or in the noise, I turn up the gain
<G>. 

The K2's tuning rates are variable in three steps from very fast, about 100
kHz per revolution, to about 6 kHz per revolution, and on down to about 1
kHz per revolution. The K2's tuning is controlled by an optical encoder, not
a pot, so the feel is very smooth and precise. The readout is in 10 Hz steps
but, thanks to a unique phase-locked loop (PLL) design used in the local
oscillator, the tuning is smooth with no 'steps'. The PLL local oscillator
is also very quiet electrically, avoiding the phase noise usually associated
with many PLL local oscillators that shows up as excess noise
indistinguishable from normal background QRN. The K2 does this by using a
PLL that tunes in about 5 kHz "steps" and then varies the PLL reference
oscillator's frequency to tune smoothly in between those steps. So the
tuning has the true smooth feel and spectral purity of an excellent "analog"
oscillator with the accuracy and stability of a good PLL. The dial reads out
in 10 Hz steps. The logic design limits the absolute accuracy to about 20 or
30 Hz, although it's not unusual for the K2 display to be within 10 Hz of
the actual frequency. 

I can't speak in any great detail about the protection circuits in the
finals for either the KPA100 or the K2. I know they both withstand repeated
transmits into an open load at full power setting without harm. The finals
in both the basic K2 and the KPA100 are very conservatively rated, handling
rather severe overloads and operating stresses without trouble.

Ron AC7AC