[Elecraft] RF on power to K3 question

[Ron D'Eau Claire]

Don, a spike is not a concern with choke for RF in the range of a few
millihenrys such as you created winding a few turns through the ferrite
core, but a larger value choke such as is often used for suppressing
generator hash and noise on a d-c line can do damage. 

What happens is that whenever current flows through the choke a magnetic
field is created around the windings. When the current stops, that magnetic
field collapses producing a pulse in the winding. With small value chokes,
such as the choke you made winding the wire through the ferrite core, the
pulse is very tiny and of no concern. 
But that pulse can be as high as several hundred volts with larger value
chokes, even working from a 13V supply. That would be plenty to do serious
damage to the K3 and most other 13V electronics you may have on the circuit.


Batteries are typically lousy conductors at RF. Putting a capacitor across
the d-c line provides a low-impedance path for any RF on the line. That
capacitor is usually built into any good rig, and the K3 is no exception. It
has both a capacitor across the line and an RF choke in series with the
power line where it enters the rig. 

73,

Ron AC7AC

-----Original Message-----

I am asking the question simply because I was warned by another ham to 
consider the possibility of a power spike on the feed to the K3 with the 
choke by another ham.   He was not fully sure and suggested that I post 
the question to the folks who might really know the answer.

Plus if it is good practice to put a CAP across the batteries for the 
way I am doing my power to help with a clean signal, clean power and 
better battery life I want use good practice.

If I had not been prompted by the ham who suggested a CAP I would have 
never asked the question.

Power is an SGC power cube good for 500w.  Antennas are a 2 WL loop for 
160m and a dipole and the shack is on the second floor.

Maybe the answer to the question is so obvious that it just shows my 
total ignorance.  Hey but I do learn slowly at times :-).  Example I now 
work split and if you remember those posts from me on that topic I think 
everyone wanted to hit me in the head with a baseball bat.

Like I indicated right now everything is working real good and I have no 
problems, but I dont want to be in the process of creating new ones.

Cheers
Don