[Elecraft] K3: Would not it be nice...

[Larry Phipps]

For a graphic representation of Joe's point, check out the BDR section 
of my LP-PAN web page at http://www.telepostinc.com/LP-PAN.html

I ran some tests of the K3/LP-PAN combo for very close in interference. 
The phase noise issue pointed out by Joe can be seen quite easily in the 
panoramic display. As you slide the interfering signal toward the wanted 
one, the noise sidebands of the interfering signal become higher than 
the noise floor, and eventually louder than the desired signal. In my 
test, I slid a very clean S9+63dB signal from an analog HP generator 
toward a 3uV desired signal, and the noise sidebands were just audible 
at a bit over 3 kHz spacing. With the interfering signal at S9+18dB, the 
sidebands could be heard at about 800 Hz spacing. With this strength of 
interference, the interfering signal had to be within about 200 Hz to 
wipe out the desired signal. This would be worse with a synthesized rig 
as the interference, of course, or a signal with modulation (even CW). 
At this signal level (just below the HAGC threshold), the K3's DSP 
dynamic range is high enough that AGC could be disabled, avoiding 
pumping. It's a moot point, however, since you're not likely to find 
interference this clean in practice, unless your neighbor has a xtal 
controlled QRP rig ;-)

73,
Larry N8LP



> ------------------------------
>
> Message: 49
> Date: Wed, 2 Apr 2008 22:29:33 -0400
> From: "Joe Subich, W4TV" <lists at microham-usa.com>
> Subject: RE: [Elecraft] K3: Would not it be nice...
> To: "'Arie Kleingeld PA3A'" <pa3a at hccnet.nl>,
> 	<elecraft at mailman.qth.net>
> Message-ID: <007101c89532$8dd63bb0$0400000a at laptop>
> Content-Type: text/plain;	charset="US-ASCII"
>
>
> Nobody makes 500 Hz IMD dynamic range measurements - they 
> are meaningless but that is what it would take to get both 
> interfering signals inside the passband of the 2.7 KHz 
> roofing filter.   
>
> Sherwood has made some very close in blocking dynamic range 
> measurements but I do not know if he has released that data. 
> The essence of the private e-mail is that even at 1 KHz the 
> limiting factor in the K3 is not blocking but phase noise 
> performance of the K3 and/or the interfering signal. 
>
> The final analysis is that key clicks and phase noise from
> signals less than 1 KHz way would be more of a problem than 
> either IMD or blocking. 
>
> 73, 
>
>    ... Joe, W4TV 
>