[Elecraft] CP1 Power Handling

[Robert Friess]

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.

73,
Bob, N6CM

----- Original Message ----- 
From: "Linden, Mike (BRC-Hes)" <Mike.Linden at boschrexroth-us.com>
To: <elecraft at mailman.qth.net>
Sent: Tuesday, March 07, 2006 6:33 AM
Subject: [Elecraft] CP1 Power Handling


  Does anyone know what modifications would need to be made to the CP1
Directional Coupler in order to get it to handle 200W at 20dB
attenuation?

  I'd like to use the CP1 as a cost effective means of extending the
useful range of my OHR WM-2 QRP Wattmeter, but 30dB is more attenuation
than I want and the power handling at 20dB is not high enough.

  Thanks, Michael N9BDF
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