[Elecraft] [K3] Noisy K3 receiver

[Bob Naumann]

There's something about Cookie's description of how one can hear noise that
makes me think that perhaps some of these "noisy" K3 comments are due to
having an expectation that is simply not realistic.

I get the impression that the expectation may be that at some point, with a
given signal strength, and enough signal to noise ratio, you will hear no
noise at all. I know this is false - unless you are using FM and the
receiver is locked on that one signal. Even under such a "full quieting"
situation, you can still hear lightning crashes through the FM signal if
they're strong enough.

The only other way that this would happen is if we were removing the noise
using DSP techniques, and re-creating the desired signal absent of the noise
that will always be there. I have tried such DSP stuff, and what remains
does not sound all that good to me, and it needs to be used sparingly.

When we're listening to CW or SSB, the level of the signal is constantly
changing in amplitude from both fading and just from the constant waveform
variance. If the AGC is set to a value (slow) that holds the gain down
during the variances, it will mask the apparent amount of noise that we
hear. It’s not gone, but we don't hear it as much. To confirm this just
switch from fast to slow AGC and back to fast on most any receiver and you
will notice this phenomena. The point is that there will be noise within
your pass band regardless of how narrow it may be and how strong the signal
may be that you are listening to. 

Am I recognizing an unrealistic expectation by users of the K3 (or most any
receiver) or am I just misinterpreting this comment? 

73,

Bob W5OV

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of WILLIS COOKE
Sent: Saturday, December 19, 2009 11:37 AM
To: don at w3fpr.com; Elecraft Reflector
Subject: Re: [Elecraft] [K3] Noisy K3 receiver

There are two ways to hear noise that comes from the antenna.  If you are
hearing it while hearing a CW tone, it is strong enough to compete with the
signal and about all you can do is narrow the band width or mentally filter
it.  If the noise is blanked by the key down signal, but you are hearing
it in the pauses it can still be annoying and you can still perceive the
receiver to be noisy.  In the latter case, changes in the AGC, or RF gain
can be effective and reduce the annoyance.  This is primarily why I like my
slope at about 6 instead of 10.  But, I am mostly a CW operator with some
SSB.  I don't operate AM or FM with my K3 which would certainly have
different requirements.  Also there is a difference in what is appropriate
for weak signal operation or strong signal operation.  In a contest
situation you repidly switch between strong and weak signals so you probably
would prefer a compromise setting.
 Willis 'Cookie' Cooke 
K5EWJ 




________________________________
From: Don Wilhelm <w3fpr at embarqmail.com>
To: elecraft at mailman.qth.net
Sent: Sat, December 19, 2009 9:23:08 AM
Subject: Re: [Elecraft] [K3] Noisy K3 receiver

Maarten (and all),

There are two separate noise sources to be considered here, and it is 
important to separate them.  One is the internal receiver noise, and the 
second is demodulated noise that comes into the receiver via the antenna 
port.

For anyone who suspects that the K3 itself is noisy (because of internal 
noise), I encourage those owners to do an MDS measurement.  If the 
internal noise is excessive, the MDS will be greatly reduced - MDS is 
the minimum signal level that can be detected above the receiver noise 
floor.  The Elecraft XG1 or XG2 is an inexpensive signal generator that 
will do the task - and the instructions for measuring MDS are in the 
manual.  If your K3 is not 'up to par', then that problem can be fixed.

OTOH, if the noise is coming into the receiver on the antenna port, 
there is not much that can be done to eliminate it - it is just like any 
other "signal" coming in from the antenna.
The K3 does offer tools such as the attenuator and AGC adjustments that 
can better handle than noise.  Unfortunately, there is not a "one size 
fits all" solution because each source of noise is different in its 
character and amplitude.

I cannot comment intelligently to those who are comparing the K3 audio 
noise output with that of another receiver because I do not have access 
to the receivers they are comparing.  I can only guess that the 
difference may be due to differences in receiver gain, AGC action, 
bandpass width, or the shaping of the audio spectrum.  Without doing 
actual measurements, these variables cannot be quantified.

73,
Don W3FPR

Maarten van Rossum wrote:
> I hope that with the help of this topic on the reflector, I too am able to
> set my K3 correctly for my circumstances so I too can enjoy noise free
> reception.
>  
>
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