[Elecraft] Noisy K3 receiver

[Don Wilhelm]

Arie,

As Wayne explained, the K3 has plenty of audio gain, and yes, the audio 
gain can be advanced sufficiently to hear the internal receiver noise, 
and even hear it as a mild 'roaring' noise.
Gains 'all to the right' is not a good way to compare two receivers - 
ideally one would have to compare the audio at a level where the same 
signal produces the same amount of audio for both receivers.  You can 
achieve that by using a steady signal source (a signal generator is 
ideal) that produces a signal level near S-9 and then connect the FT1kMP 
audio to a computer running an audio spectrum analyzer application (like 
Spectrogram) which will display the signal amplitude.  Do the same with 
the K3 and set the AF Gain to produce the same signal amplitude.
You will then have the same overall gain set for both receivers.  You 
are attempting to compare the receiver internal noise level and not the 
receiver gain, so for a valid comparison, the gain of both receivers 
must be made the same for the test.

You indicated that the noise increased on your K2 when you disconnected 
the antenna.  AGC could do that, or too high a setting of the AF Gain.
If you have any signals in the receiver passband when you have the 
antenna connected, the AGC would have held the receiver gain down (how 
much depends on your AGC SLP and TH menu settings) - then when the 
antenna is removed, the K3 will go to full gain, and you will be hearing 
the internal noise at full gain.  Actually noise evaluation should be 
done with the AGC off so its action will not influence the test outcome.

My K3 has enough audio gain that I can just barely hear the internal 
receiver noise with the AF Gain set at about the 8:30 position.on the 
internal speaker if the menu AG Gain parameter is set to HI, and about 
the 11:30 position if AG Gain is set to LO.

With a dummy load connected (or the antenna disconnected), if I leave 
the RF Gain at maximum and set the AF Gain to the point where I can 
barely hear the receiver noise, then connect an antenna, the noise level 
always increases - this is the reverse of your test, but it should be 
just as valid.

The only way I can get my K3 to have almmost as much noise with the 
antenna removed as it has with the antenna connected is to set the AGC 
Threshold to its minimum value (002).  My AGC Threshold is normally set 
at 008.  As a side-point, I set my AGC SLP at 002 because that produces 
a response similar to that of the K2 which I liked - weak signals sound 
weaker, strong signals stronger and I can judge that without reference 
to the S-meter.

If you wish to try some other tests, let me know and I will try to help.

73,
Don W3FPR

Arie Kleingeld PA3A wrote:
> Let me throw in a penny please.
>
> Just for comparison:
> FT1kMP : all controls full gain (except AF of course), antenna connected.
> Then disconnect antenna and listen: nearly no audio, only the receiver
> noise.
>
> K3: do the same. Difference is that when I disconnect the antenna, the noise
> coming from the speaker is much louder! So the receiver noise is much
> louder?  I thought that that might come from the dsp design. (I think that
> that is what Don meant)
>
> I am open for enlightenment.
>
> 73
> Arie
>   
>