[Elecraft] KX3 12kHz audio spike

[David Gilbert]

That is absolutely a real effect.  Back in the mid-70's I was a product 
engineer responsible trying to sell tuning diodes to the TV tuner 
industry.  UHF tuners in the U.S. back then were still almost all 
mechanical, and even though the rest of the world had pretty much 
already converted to electronic tuning it was a tough sell. Those RF 
engineers back then were VERY conservative but they really, really knew 
their stuff.  I remember a couple of them giving me a mini-primer on how 
they designed a mechanical tuner, and it was fascinating.  Coupling from 
the oscillator to the mixer was partially affected by current flow in 
the very heavy stamped chassis (i.e., ground) partition, and they 
described how if they needed more coupling they just punched a hole here 
and there to direct the current where it would have more effect.

It might be easy to dismiss such effects as being at VHF frequencies, 
but that would be a mistake.  Currents most certainly do not flow 
uniformly in ground planes, and coupling effects can be real whenever 
significant gain is involved.

73,
Dave   AB7E





On 8/6/2013 1:46 PM, Jim Brown wrote:
>
> Or perhaps even a circuit layout issue. On several occasions, I've 
> urged the Elecraft engineering team to attend one of Henry Ott's 
> excellent EMC workshops. Henry talks about keeping track of where the 
> current is flowing -- ALL of the current, not just the "intended" 
> current, and he talks about the invisible schematic hidden behind the 
> "ground" symbol, which is one of the most common ways we lose track of 
> the return current. If, for example, the current associated with that 
> 12 kHz clock happens to share a return current path with an audio gain 
> stage, it gets added to the audio. It's the same sort of mechanism 
> that if it's at the junction of the box and the outside world we call 
> a "Pin One Problem."
>
> 73, Jim K9YC