[Elecraft] [K2] lack of sensitivity...?

[Don Wilhelm]

Gil,

Hopefully you are not being confused by the amount of audio reserve.  
The audio in the K2 is adequate, but limited, while the K1 has an LM386 
audio driver followed by an LM380 amplifier and has lots of reserve audio.

It is difficult to tell what you are describing without some form of 
measurable signal injection.  I would suggest that you tune around the 
ham bands for the weakest signal that you can find and compare those.  
If you try to compare raw signal audio, the K1 will win every time, but 
you really need to determine "what is the weakest signal that I can 
receive on this radio"  In that context, the K2 will usually be better 
than the K1.

What I do as a sanity check for every radio I repair is to set the 
output of my HP8640 signal generator at -130 dBm and see just how far 
above the receiver noise level that signal is displayed on the 
Spectrogram screen.  While that is not a true MDS measurement, it does 
give me some assurance that the receiver will be acceptable - the 
Spectrogram display shows me how much above the receiver noise floor 
that -130 dBm signal rises.  If I were to go to pains and add additional 
attenuators and calculate the MDS of each receiver, I would find them 
quite close - my expectation for the K2 would be in excess of -135 dBm 
while the K1 and the KX1 would be close behind at about -132 dBm  A 3 dB 
difference, -- that is twice the receive sensitivity.  You cannot hear 
that difference with your ears unless you are comparing signals just 
barely above the noise level, but you certainly can measure it.

All that information does you no good in operation unless the 
atmospheric band noise is less than the MDS of the receiver.  Not 
typical on the bands 20 meters and below.

73,
Don W3FPR
On 8/30/2012 6:36 PM, Gil G. wrote:
> Thank you everyone for your suggestions.
>
> I did have one bad solder joint on TR7, fixed it by soldering one lead on top. Maybe the problem is related to that.
> Tuning L34 doesn't seem to do much of anything. There was no 3.3pf capacitor for C22 on the RF board, but I had one 2.7pf left over after finishing, so I assumed I had to use that..
> I did try to compare the K2 with the K1 without the ATU, it does make a difference, now it is closer (with preamp on). Maybe I'm being too picky. I was assuming the K2 would run circles around the K1.
> Don, what kind of additional data can I gather that would help make a diagnosis?
> I do not have an RF signal generator, but I have a K1 and a dummy load.
> It is peculiar that the 20m band is the most affected… Could filter setting be the cause?
> I do have spectrogram on my iPod, but the interface is different than on the PC version, not usable for filter adjustments.
> (I use a Mac…)
>
>