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*Subject*: R: R: [amsat-bb] modeling qha*From*: "i8cvs" <domenico.i8cvs@xxxxxx>*Date*: Tue, 20 Apr 2004 19:11:52 +0200

----- Original Message ----- From: Wallace Strom <kg4yuw@arrl.net> To: i8cvs <domenico.i8cvs@tin.it> Cc: AMSAT-BB <amsat-bb@AMSAT.Org> Sent: Tuesday, April 20, 2004 5:15 AM Subject: Re: R: [amsat-bb] modeling qha > Domenico, > Thanks for the reply. Hello Wallace,KG4YUW I tried to send you a file 3 MB long but it was rejected at your address kg4yuw@arrl.net Do you have another address where i can send the above file to you ? > I am a little confused - I can model the feed point at the top or the bottom. > Is the top -endfired and bottom backfire ? No ! The feed point on top or the feed point on bottom can be connected to radiate endfire or backfire and it depends on how you connect the small bifilar and the large bifilar to the infinite balun and this is why i would like to send you a drawing to show it. In simple words If you connect the small bifilar and the large bifilar following the drawing fig. 8-17 Chapter 18 page 8-16 in "The Satellite Experimenter's Handbook" of K2UBC than the QHA radiates endfire upward i.e. in the opposite direction of coax connector. Since the small bifilar and the large bifilar are left hand wounded than the QHA radiates RHCP upward or endfire in that drawing with that connections. If you connect the small bifilar and the large bifilar as per fig 22-9 of W2DU book "Reflections" Chapter 22-15 "supposing" that the drawing is the same of K2UBC book than the radiation is RHCP backfire downward or in direction of the book and not in direction of the reader. > > Other questions - should the second feed point be 90 degrees out of phase from > the first? At the frequency of operation the perimeter of the small loop is designed to be 1.016 wavelenght in order to get a capacitive reactance -jX with the same value of R wich is the real part of the impedance. When the impedance is Z=R-jX with R=X than the current lead the voltage by 45 degrees At the frequency of operation the perimeter of the large loop is designed to be 1.120 wavelenght in order to get an inductive reactance +jX with the same value of R wich is the real part of the impedance When the impedance is Z=R+jX with R=X than the current lags the voltage by 45 degrees. Since the small bifilar and the large bifilar are connected in parallel to the infinite balun than -jX and +jX cancel out but the total current phase shift is 45+45=90 degrees thereby generating circular polarization and the impedance is theoretically purely resistive Z=R+j0 because of self-matching. Should I model the antenna's at 40 ohms? (W2DU) Should the SWR > for both feed points match? To get the above conditions it is mandatory to model the QHA following dimentions of table 8-6 of K2UBC book or page 22-16 Chapter 22 of W2DU book with the same results. More and detailed info on this matter in AMSAT journal May/June 2004 > > Thanks > Wally > kg4yuw > 73" de i8CVS Domenico ---- Sent via amsat-bb@amsat.org. Opinions expressed are those of the author. Not an AMSAT member? Join now to support the amateur satellite program! To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**References**:**modeling qha***From:*Wallace Strom

**R: modeling qha***From:*i8cvs

**Re: R: modeling qha***From:*Wallace Strom

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