The example wasn't meant to be K3 specific, but rather to graphically
show the concept of why transmitted phase noise is such an important
factor with close in interference. The overall BW in these examples is
actually >192 kHz!
Larry N8LP
Joe Subich, W4TV wrote:
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: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Larry Phipps
Sent: Thursday, April 03, 2008 9:15 AM
To: [email protected]
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" <[EMAIL PROTECTED]>
Subject: RE: [Elecraft] K3: Would not it be nice...
To: "'Arie Kleingeld PA3A'" <[EMAIL PROTECTED]>,
<[email protected]>
Message-ID: <[EMAIL PROTECTED]>
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
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