[Elecraft] CP1 Power Handling

[Larry Phipps]

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)" 
> <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
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>
>