[Elecraft] [K2] Sensitivity Spec

[Edward R Cole]

Steve,

I ran your parameters thru my NF program for three stages using:
1.2 dBNF of 1st stage with 17-dB gain (typical DEMI 10-GHz xvtr spec)
followed by 0.1 dB cable loss
1.0 dBNF 2nd stage which nominal for a 144-MHz xvtr and used 10-dB gain
followed by0.1 dB cable loss
K2 10-dBNF
Bw = 500 Hz
MDS = -151.2 dBm
change gain of 2nd stage to 15-dB results in MDS = -151.4 dBm so 
10-dB gain is sufficient

The K2 with 10-dBNF has MDS = 137.3 dBm
Thus you should see 13.9 dB increase in sensitivity (MDS).

But since sky noise temperature at 10-GHz is typ 10K not sure how 
much noise rise will be seen.
At 2m Tsky is about 250K (in a perfectly quiet environ) so same 
system looking at the 2m sky has MDS = -146.2 dBm
At 10m Tsky is about 5,000K (guessing) and MDS = -134.5 dBm

Obviously the K2 10-dBNF is sufficient on 10m, assuming adequate 
system gain to drive the mixers.

73, Ed - KL7UW
-----------------------------------
From: Steve Kavanagh <skavanagh72 at yahoo.ca>
To: <elecraft at mailman.qth.net>,  <donwilh at embarqmail.com>
Subject: Re: [Elecraft] [K2] Sensitivity Spec
Message-ID: <1122135791.3077810.1502906517770 at mail.yahoo.com>
Content-Type: text/plain; charset=UTF-8

Thanks for your comments, Don.  When you test K2's, can I assume you 
have the signal generator connected directly to the K2 (or through an 
attenuator) with no antenna connected?

Normally, one might hope that a preamp would provide some improvement 
in receiver noise figure (and hence MDS, sensitivity, noise floor), 
or there isn't much point in having it. I've never run into an 
intermodulation or blocking problem on 10 GHz (sideband noise issues 
tend to dominate the *rare* strong signal scenario) so I expect to 
leave the K2 preamp on in an attempt to maximize the sensitivity

I agree that most often transverters have lots of gain but I noticed, 
with the particular combination I have, that the increase in receiver 
noise output resulting from turning on both the 10 GHz-to-144 MHz and 
the 144 MHz-to-28 MHz transverters was only about 7 dB (K2 preamp on, 
AGC off) compared to the K2 alone, rather less than usually seems to 
be the case, so I was afraid that the front end noise might not 
dominate the overall receiver noise.  The intermediate transverter 
does have relatively low gain, by design.  With a couple of tweaks 
and a minor repair in the transverters I've now increased this ratio 
by a couple of dB.

Since the 10 GHz transverter noise figure was measured by the 
manufacturer at 1.2 dB and the K2 is something closer to 10 dB the 
increase in noise may not have to be all that much for the system to 
be working right.  I haven't felt up to doing all the necessary math 
this week to make sure, especially without a reliable number for the 
K2 noise figure.  Most likely I'll try it out in the 10 GHz and Up 
contest this weekend and if it proves to be deaf compared to others' 
rigs, I'll have to delve deeper.

73,
Steve VE3SMA
--------------------------------------------
On Tue, 8/15/17, Don Wilhelm <donwilh at embarqmail.com> wrote:

  Subject: Re: [Elecraft] [K2] Sensitivity Spec
  To: "Steve Kavanagh" <skavanagh72 at yahoo.ca>, elecraft at mailman.qth.net
  Received: Tuesday, August 15, 2017, 8:29 PM

  Steve,

  Typically, the receiver is limited by the noise
  floor, so the MDS will
  not change much
  whether the preamp is on or off.? While the preamp will
  increase the strength of the signals, it also
  adds to the noise floor.

  Generally a transverter will have a low noise
  preamp with plenty of
  gain, so there is
  usually no advantage in running the transceiver with
  the preamp on.? Use your ears while listening
  to a strong signal to see
  if you can detect
  overload of the receiver preamp - if so turn it off,
  but if there is no overload distortion, you can
  leave it on.

  Typical MDS
  measurements are made at 500 Hz.
  I typically
  do a quick test of the sensitivity of K2s that I repair.? A

  -130dBm signal should be detectable above
  the receiver noise floor.? For
  that test,
  I have observed that it makes little difference whether the

  preamp is on or off.? So I would suggest
  you test whether strong signal
  performance
  is better with the preamp on or off.? My wager is that you

  will choose to leave it off unless your
  transverter(s) have negative
  gain on RX.

  73,
  Don
  W3FPR


73, Ed - KL7UW
   http://www.kl7uw.com
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