WHY "CFA" ANTENNA's WORK !

It would appear that very little has ever been done to correct the di-pole errors. Alas most books seen not to correctly explain the field patterns around the di-pole........I found an old book obtained from a charity shop for only 50 pence and it was published back in (1912) 1924 the fourth edition all about Electricity and Magnetism by S.G.STARLING .......Head of the physical department, Municipal College, West Ham......

Crossed Field Antenna's known for short as "CFA" is a good example of a team of people in Scotland understanding what is wrong with the di-pole and doing something about it....

Alas skeptics about "CFA's" condemn the theory because they are lacking in insight and understanding.

THE DI-POLE FAULTS

  1. The TEM wave is spread over half a wavelength.
  2. The "H" field starts off before the "E" field.
  3. The "E" field is curved.
  4. The "H" field is curved in a circle.
  5. The impedance along the element is NOT constant.
  6. The di-pole produces a near field effect.
  7. The "Q" of the di-pole causes a Bandwidth problem.
  8. "EH" radiation does not take place at the di-pole element.
  9. "E" to "H" balance of levels is not constant.
  10. High Currents and High Voltages are produced a possible cause for TV I.
  11. Ground absorbs the high voltage "E"

THE "CFA" CORRECTIONS

  1. The "CFA" can be made small 1 or 2% the size of the wavelength
  2. The "H" field is generated with a small Capacitor and its phase can be adjusted reference the "E" field.
  3. The "E" field can be made vertical with a conical element.
  4. The "H" field in this case is wanted to be a circle for omni-directional use.
  5. The impedances are constant (at a certain frequency).
  6. Because the Phase and Levels are correct no Near Field errors.
  7. The Bandwidth is very flat.
  8. Radiation starts at the "CFA"
  9. No Sky wave is produced.
  10. Less trouble with TVI (less Current and less Voltage).
  11. Most of the Energy goes in the wanted direction (very narrow lobe).
  12. Less ground absorption, "E" field, due to the lower voltage and its direction

NOTE: "CFA,s" can be made on any Frequency !

Build one and see for yourself ignore skeptics they soon creep into the woodwork

BEWARE of measuring the "CFA's" field strength close up with a di-pole that is bigger than the "CFA" beam width only do it at a distance where you expect the width of the beam to be greater than the di-pole capture area !

Thoughts for the day !

Little Boy to his Dad early in the morning "see Dad Darks gone OFF" and it had....G3RFL

I started out with Nothing and I have Managed to keep Most of it......G3RFL

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Defects of CFA Todate are :

CFA defects are that on receive they have a poor capture area of power sent from a normal RF system hence a loss but a small gain in the fact it converts the small "E" "H" field without much loss back into the antenna coax unlike a di-pole that is very lossy... So if you have a CFA only 2% the size of a di-pole then it will only get 2% of the energy so its another balancing act to do...?.... Have Fun ! G3RFL

This does open the answer to why two CFA's near to each other don't upset the SWR too much.

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