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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