[Elecraft] KPA500 - ground wire between the AC earth and RF output socket

[Jim Brown]

On 9/4/2011 5:22 PM, Johnny Siu wrote:
> Hello Jim,
> Thanks for your reply.
> Yes, I understand the rationale behind.  However, I don't understand 
> why the green ground wire is so specifically linking the AC Earth 
> Terminal to the case of RF output socket instead of other metal part 
> of the KPA500.  Could you please enlighten me on that?

That's a question that really relates to the internal design of the KPA 
itself.  The concern is what happens in the case of a lightning strike, 
which is usually strongest on antennas and on the power line. They can 
generate strong currents, and a good design for earth and chassis 
bonding will try to have those currents stay outside the box -- that is, 
not flowing through the circuit boards or the chassis. The best way to 
do that is to have those external wires bonded to the same physical point.

> I have another question.  I live in a multi-storey apartment.  
> Split-type airconditioners are everywhere so that man made RFI can 
> come to my radio / linear amplifier via the AC Earth.  To avoid this, 
> can I put RF choke between the AC Earth and the ground (i..e. metal 
> case) of the KPA500 ?

NO!  This defeats the safety of the bonding for lightning protection!  
What you CAN do is implement proper bonding of your power system, 
carefully following the rules in your country.  My tutorial primarily 
addresses the rules in North America, and there are some variations from 
one country to another. But the general rule that works everywhere is 
that everything must be bonded together by the shortest practical path 
-- all ground electrodes (rods), building steel, power system neutral 
(at the entry panel), radio equipment, arrestors for telephone and cable 
TV, etc.  Again, study the tutorial.  As it turns out, the SAFEST 
bonding is also the QUIETEST bonding.

Another important point.  If you're using any sort of long wire antenna, 
whatever your chassis is connected to is an important part of the 
antenna -- the return current of the antenna has to go SOMEWHERE.  If 
you open that circuit (with an RF choke), you may hear less noise, but 
the antenna won't transmit nearly as well.  If you're using a coax-fed 
antenna, you CAN add a common mode choke to it to kill the noise picked 
up on the coax.  See my RFI tutorial for details on that.

73, Jim K9YC