Monday, June 3, 2024

Mini EFHW transformers - power handling test

 I was asked if the mini EFHW transformers (designed by DG1JAN) can handle 10W. I guess it depends of the ambient conditions. Same as people whose KX2 overheats and they need to install side radiators. Mine never does - probably because it is rarely warmer than 85°F in my area and I don't use digital modes.


Test conditions

  • Location: Parc de la Cité, grassy field
  • Radiator for 18MHz mounted on Sotabeams carbon mast (6m)
  • Transformer with ratio 1:54 and FairRite 5943000601 toroid.
  • The rig indicates DWR 1:1.1 without tuner.
  • My weather app says it is 21°C (70°F) on shade
  • No wind, clear sky
  • The antenna and the transformer are fully exposed to the sun
  • The rig is KX2 and I shield it from the sun with my body
  • Calling VVV DE VE2WLD VE2WLD with 10 seconds intervals at 10 watts CW.


Results

After 10 minutes of work (with a total of about 2 minutes interruptions), I can't detect any heath coming from the transformer.

After another 15 minutes of work without interruption, there is a hint of warmth coming from the transformer. 

The KX2 indicates internal temperature swinging from 41°C to 47°C. The right side of the rig is noticeably warm. Much warmer than the toroid.


Conclusion

The transformer handles the temperature better than my rig. 

I would use the 601 version at 10 watts in most of my activations (usually in the forest, some breeze near the summit, no extreme heath).

I would stay at 5 watts or use the 501 version (double length) toroid if the day is particularly hot.

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