Bob, have you seen any difference between stacked cores and solid ones
of the same total thickness? In designed my wattmeters, I found more
heating with stacked cores... at least for one combination. The FT50B
core is the same thickness as 2.66 stacked FT50 cores, or 2 FT50A cores.
Larry N8LP
Robert Friess wrote:
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)"
<[EMAIL PROTECTED]>
To: <elecraft@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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