Power Handling capability

The power handling capability of Common Mode Chokes, including ours, is determined almost entirely by how hot the ferrite core gets due to power dissipation caused by insertion loss.  If the choke is ineffective in reducing common mode current, then additional heating can occur due to the residual common mode current that flows through the choke.  However, if the choke is effective - as it should be - in blocking common mode current, this additional heating is negligible. 

The Black Beauty choke enclosures are well ventilated and enable the choke to handle about 80% more power than is possible with a sealed enclosure. 

Nevertheless, the choke dissipates some power and experiences a temperature rise that should not be ignored.  

The factors that affect the internal temperature of the choke are:

1. The average power applied to the choke (PEP transmitter output minus Feedline loss) times the Duty Cycle, 
2. The ambient air temperature outside the choke's enclosure,
3. The frequency of operation.

Duty Cycle is determined by the mode of operation.  Some of the common ones are summarized here:

     Uncompressed SSB normal speech, or casual intermittent CW:  20-25%

     Continuous FT8/4:  43%

     Continuous Highly Compressed SSB:  50%

     High speed contest "run" station on CW:  50%

     Long winded AM:  100%

     Long winded RTTY or certain other digital modes:  100%

Example:  A station running 1500 Watts PEP output to a coax feedline with 1/2 dB loss (85 feet of RG213) will apply about 1300 watts PEP to the choke. The average power applied to the choke (located at the feed point) will then vary according to the operating mode, as seen here. Keep in mind that these are just the maximum average power levels expected at the choke (after feedline loss) for various operating modes. These are NOT the power limits of the choke.

Average Power that appears at the choke for the above 1500W example:

     For casual intermittent CW or uncompressed SSB (DC = 25%): 325 Watts

     For a long winded AM station with normal speech:  350 Watts

     For FT8/4 (DC = 43%):  560 Watts

     For a CW contest "run" station or highly compressed SSB: 650 Watts

     For continuous RTTY:  1300 Watts

These are NOT the power limits of the choke.  The power handling ability of the choke for each Duty Cycle has been calculated for you. This information is found in the "Power Limit by Band and Mode" charts. There is a chart for each of the various modes (and, therefore, the various Duty Cycles) of operation. Use the buttons below to access these charts.

Use the chart that applies to your intended mode of operation.  Then find the curve for the band of interest and you can readily see how much power you can run at any given ambient temperature.

These plots are conservative and will keep the core temperature below 175F. Under no circumstance should the core temperature ever be allow to reach 230F (12% lower than the Curie Temperature).  This temperature will begin to damage the core and enclosure.  The margin between these two temperatures is what provides a measure of conservatism.