[Elecraft] Tuning clunks: technical explanation

Geoffrey Mackenzie-Kennedy gmk at gm4esd.fsworld.co.uk
Wed Mar 28 05:19:25 EST 2007


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" <n6kr at elecraft.com>
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
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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