[K2] Sensitivity Spec

[Elecraft mailing list]

I'm just trying to evaluate if I have the gain distribution right for a K2 used as an IF for a 10 GHz transverter, through a 2 m transverter mounted inside the QRP top.  The K2 manual gives a specification for the MDS but fails to define the bandwidth at which it is measured.  Sherwood's receiver table lists some measured values at 500 Hz bandwidth but fails to note whether the preamp is on or off for these measurements.  So I am not quite sure what the sensitivity should be.  

Can anyone clarify?

73,
Steve VE3SMA
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[Don Wilhelm]

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

On 8/15/2017 4:10 PM, Steve Kavanagh via Elecraft wrote:
> I'm just trying to evaluate if I have the gain distribution right for a K2 used as an IF for a 10 GHz transverter, through a 2 m transverter mounted inside the QRP top.  The K2 manual gives a specification for the MDS but fails to define the bandwidth at which it is measured.  Sherwood's receiver table lists some measured values at 500 Hz bandwidth but fails to note whether the preamp is on or off for these measurements.  So I am not quite sure what the sensitivity should be.
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[Elecraft mailing list]

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 <[hidden email]> wrote:

 Subject: Re: [Elecraft] [K2] Sensitivity Spec
 To: "Steve Kavanagh" <[hidden email]>, [hidden email]
 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
 
 On 8/15/2017 4:10 PM, Steve
 Kavanagh via Elecraft wrote:
 > I'm
 just trying to evaluate if I have the gain distribution
 right for a K2 used as an IF for a 10 GHz transverter,
 through a 2 m transverter mounted inside the QRP top.  The
 K2 manual gives a specification for the MDS but fails to
 define the bandwidth at which it is measured. 
 Sherwood's receiver table lists some measured values at
 500 Hz bandwidth but fails to note whether the preamp is on
 or off for these measurements.  So I am not quite sure what
 the sensitivity should be.
 
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[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 <[hidden email]>
To: <[hidden email]>,  <[hidden email]>
Subject: Re: [Elecraft] [K2] Sensitivity Spec
Message-ID: <[hidden email]>
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 <[hidden email]> wrote:

  Subject: Re: [Elecraft] [K2] Sensitivity Spec
  To: "Steve Kavanagh" <[hidden email]>, [hidden email]
  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
Dubus-NA Business mail:
   [hidden email]

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