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 <[email protected]>
To: <[email protected]>, <[email protected]>
Subject: Re: [Elecraft] [K2] Sensitivity Spec
Message-ID: <[email protected]>
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 <[email protected]> wrote:
Subject: Re: [Elecraft] [K2] Sensitivity Spec
To: "Steve Kavanagh" <[email protected]>, [email protected]
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:
[email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
