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

[Joe Subich, W4TV]

> 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

The 5 KHz and 2 KHz examples with LP-Pan and PowerSDR are "worst 
case" for the K3 and would be equivalent to using the FM filter 
for all modes.  Even at 2 KHz, the interfering carrier would be 
nearly 30 dB down the skirt of the 2.8 KHz/8 pole filter and 
any IMD between it and another signal even farther away would 
be down significantly (assuming the CW signal is centered). 

Phase noise, key clicks and transmitted IMD from other stations 
will be the limiting factor for receiver performance in the K3.  

73, 

   ... Joe, W4TV 
  




> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Larry Phipps
> Sent: Thursday, April 03, 2008 9:15 AM
> To: elecraft at mailman.qth.net
> Subject: RE: [Elecraft] K3: Would not it be nice...
> 
> 
> 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
> >   
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft    
> 
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com