Wayne,
Thank you for your comments, all understood. I know about 4 am sessions,
been there <g>. Due to time restraints I have yet to examine in detail the
cause(s) of my K2's PLL (i.e. the Reference plus VCO) behaviour in the
presence of strong incoming signals, but from spectral analysis it does
appear that situations do arise when strong incoming signals (and products?)
gang up to upset legitimate lock.
The extreme case that I have observed with the K2 occurs when tuning through
a strong 40m BC station whose carrier level is in the region of -10dbm, and
other BC stations are within the same band at similar carrier levels.
Behaviour is normal while the target BC station enters the IF passband up to
the point where the carrier is at zero beat with the BFO. Continuing to tune
the receiver away from the BC signal does not change the signal's position
in the IF passband until the displayed frequency is roughly 1 kHz away from
the BC station's carrier frequency, at which point the receiver lets go and
returns to normal operation. If the BC carrier is modulated at a very high
level the 'let go' point can be more than 1 kHz away from the carrier
frequency. If I stop tuning the receiver away from the BC station at some
point between the carrier frequency and the 'let go' frequency, the BC
carrier remains at or within 100 - 200 Hz of zero beat with the BFO, further
observation required. Reduce signal levels and there is no problem.
It does remind me of the not uncommon problem where a PLL can be upset by
intruding external sources, descibed to me many years ago as the 'Monkey in
Kitchen' problem.
My apology for this brief response, I am leaving for Luxembourg shortly.
73,
Geoff
GM4ESD
----- Original Message -----
From: "wayne burdick" <[EMAIL PROTECTED]>
To: "Elecraft Reflector" <[email protected]>
Sent: Wednesday, March 28, 2007 4:19 AM
Subject: [Elecraft] Tuning clunks: technical explanation
The K2 is a careful balance between high performance, small size, low
current drain, and low cost, while at the same time using through-hole
parts to make it easy to build. As the principle designer of the rig, I
can tell you that this required a number of design tricks to accomplish.
The "clunks" are a side-effect of one of these design choices. A little
background will help explain this. I'll also briefly describe what could
be done about it.
<snip>
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