Checking K2 sensitivity...

[Steve Kallal]

I am the second owner of K2 #2289. I've built and added a number of options.
But I wonder about its rx sensitivity. I often have to use the preamp on 30
and 20 meters to hear weaker signals. The same is not true of my 756 PRO 2,
at least on the same signals while doing an A/B comparison.

That said, I'd like to know the best way to re-check the rx sensitivity on
my K2. I still prefer it to my PRO 2 for copying CW, especially with narrow
filters kicked in. The PRO 2 has horrible ringing with narrow filters.
Otherwise, it just seems like the PRO 2 has better ears. Some how I don't
think that should be. Maybe my K2 needs tweaking.

73,

Steve N6VL

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[Darwin, Keith]

-----Original Message-----
I am the second owner of K2 #2289 ... I wonder about its rx sensitivity
... it just seems like the PRO 2 has better ears.
--------------------------

One has to be careful about confusing audio output with sensitivity.
The K2 tends to produce less audio output with weak signals than other
rigs and that leads us to conclude it doesn't hear.  What it doesn't do
is reproduce all signal levels at the same audio level.

An S9 signal is just as loud as the band noise in most rigs because
their AGCs are very aggressive & flat.  They turn the gain down for all
signals to match them to the quietest signal, effectively making audio
output constant.

The K2 has some slope to its AGC.  Loud signals produce more audio
output than quiet signals.  Band noise is quieter than signals.  So as
you listen to the K2, you don't hear much unless there is a signal
there.  The K2 is still picking up everything the Pro 2 is, it just
isn't amplifying it as much.

An interesting test would be to turn AGC off on both rigs, set both with
RF gain max and AF gain so they are the same volume, then tune in very
weak signals.  I bet they both pick them up equally well.

- Keith N1AS -
- K2 5411.ssb.100 -
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[Dave, G4AON]

There was a problem with "transmit power" and RX sensitivity on early
K2s,  my K2 serial #1892 had this problem. Basically the tuning cap(s)
in the band pass filter needed a fixed capacitor of around 10 pF across
the variable as it was right at the end of it's tuning range, you might
want to check back through the list for details.

My K2 gives 0.12 uV sensitivity for 10 dB signal to noise without the
pre-amp, and 0.1 uV with the pre-amp on.

73 Dave G4AON
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[Dave, G4AON]

The 20m low power/sensitivity bulletin on early K2s is on the Elecraft
web site is at:

http://www.elecraft.com/Apps/k2_20M_LowPower.htm

73 Dave, G4AON
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[AC7AC]

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