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Re: Re: look this dual band egg



"Aldo Marchetto" <a.marchetto@iii.to.cnr.it> writes:

 > Just a short question about using a single eggbeater/TPM as dual band 
 > antenna:
 > 
 > if you use a RHCP eggbeater for 2 meters in 70 cm, does is produce 
 > LHCP?

Excellent question!  I had not thought about it, but yes it would be 270 degrees out of phase, so if the 2 m physical arrangement was set up to produce RHCP with 90 degrees "delay," then the 70 cm polarization will be LHCP.

 > I suppose that the phasing line would be 3/4 wavelenght, reversing 
 > the polarity of the second loop. Is it correct?

Right on!  In actual practice, however, antennas of this design are truly only CP to a very great degree in the axial mode.  At angles more than 30 degrees off the axial center they become more and more elliptical until they are horizontally polarized at the horizon (in plane with the 2-axis polarization of the driven element)--ie., the first +/- 90 degrees of the full-wave driven element.  What this means to the user of an omnidirectional antenna of this design is the difference in L v. R CP will be insignificant, and even random, for > 90 percent of all satellite downlink windows and then the "potential wrong polarization" is only 50 % of the 1 or 2 minutes when the bird is directly overhead.
73,
Jerry, UA3T/K5OE

 > TNX Aldo IZ1ANT
 > Dr. Aldo Marchetto
 > C.N.R. Istituto Italiano di Idrobiologia
 > Largo Vittorio Tonolli 50
 > I-28922 Verbania Pallanza (VB) - Italy
 > Voice:  +39 0323 518357
 > Fax:    +39 0323 556513
 > E-mail: a.marchetto@iii.to.cnr.it
 > http:   www.iii.to.cnr.it



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