[Elecraft] CP1 Power Handling

[Linden, Mike (BRC-Hes)]

Robert,

  Thanks for the insight and alternate solution! -Michael


-----Original Message-----
From: Robert Friess [mailto:rfriess at usa.net] 
Sent: Tuesday, March 07, 2006 10:46 AM
To: Linden, Mike (BRC-Hes); elecraft at mailman.qth.net
Subject: Re: [Elecraft] CP1 Power Handling

Hi Michael,

I designed the CP1 for Elecraft and in the process I performed many
tests to evaluate the power handling capabilities.  The power is limited
by heating of the core and that is primarily a function of flux density
and time.  The published specification allows the rated power to be
applied for long periods of time without excessive heating.

The flux density is proportional to the applied voltage, i.e. square
root of power, and inversely proportional to the number of turns, cross
sectional area, and frequency.  For a 20 dB coupler the number of turns
is fixed at 10.  Because of the small turns count type 43 material was
chosen to provide sufficient inductance to maintain performance at the
lowest frequency. 
Unfortunately, type 43 has a relatively low Curie Temperature, that is,
the temperature at which the magnetic properties of the core disappear.
Other core materials have much higher temperature ratings and lower
loss, but they do not provide sufficient inductance for good performance
on 160 meters.

So what does all this mean?  I suggest that the easiest thing for you to
do would be to stack three cores together at each position.  It will be
easier to wind the cores if you use some sort of adhesive to hold the
cores together.  This will provide about 9 times the power handling
capability and meet your power requirement.  If you don't hold the key
down for 5 minutes even better.  You can order the extra cores from
Elecraft.