John, LA2QAA
That was an interesting message you posted to the -bb this morning. It has many true observations; however there is one serious mistake, an unforgivable error.
Quote: ......... particularly by the newcomers - who apparently, and mistakenly, think that high power is necessary. It's *NOT* . . . nor is an EME class aerial array necessary to work the LEO satellites. Ditto circular polarisation.
FACT: polarisation is *ONLY* circular along the boresight of an aerial.
Unquote. Your polarization statement is not 100% accurate. Unfortunately most antenna manufacturers, who supply/sell "alleged circular" polarized antennas do not state that their antennas are circular polarized ONLY along the boresight. They conveniently (?) do not mention that their alleged "circular polarized" antenna is only circular polarized on boresight, that it is linear polarized at 90 degrees off of boresight and is elliptical polarized of varying ratio at all angles in between!
There is however one (and only one that I am aware of) antenna design that is circular polarized over its entire radiation pattern. I refer you to the Q_uadrifilar Helix Antenna_ described by Dr. C.C.Kilgus in IEEE Trans., Vol. AP-16, July 1968, pp. 499-500. Also Bricker, R.W. and Rickert, H.H., in RCA Engineer, Vol.20, No. 5, February/March 1975. There is an excellent review by Walter Maxwell, W2DU, at http://www.IAG.net/~w2du/quadfinal.pdf.
When installed pointing to the zenith, the "ideal, theoretical" Quad Helix has 360 degree coverage in the azimuthal plane and 90 degree coverage in the elevation plane. It is circularly polarized over the entire upper hemisphere. There is no radiation in the lower hemi-sphere; the energy in the lower hemi-sphere of an isotropic radiator is uniformly distributed over the upper hemi-sphere. Hence the gain of an "ideal" Quad Helix is 3.01 dBi. However you can modify the elevation pattern to give more gain at the horizon and less gain overhead by adjustment of the overall length to diameter ratio. It is possible to adjust this ratio to give constant signal amplitude, at an earth based receiving station, from a satellite in a circular orbit where the range ratio (and hence signal path attenuation) between AOS and the zenith can be significant. This results in a little radiation below the horizon and also avoids the nasty mathematical boundary value problem at the horizon in the ideal case.
Quadrifilar Helix antennas are used on many LEO satellites for VHF, UHF, L-band and S-band communication. One of their parameters of interest to satellite builders is that they do NOT require a "ground plane" provided they are at least a quarter wavelength above the satellite structure. Hence there is negligible critical location requirement and they do not occupy satellite surface area that is required for solar cells.
The Quadrifilar Helix antenna is popular with earth based receiving stations for receiving the VHF image data signals from the NOAA weather satellites. Right-hand circular Quad Helix antennas for the 137MHz NOAA weather image signals and 137MHz left-hand circular Quad Helix antennas for receiving the ARGOS programme signals, are available from Spectrum International, Inc. Spectrum also supplies both right-hand and left-hand versions for the 2M and 70cm Amateur radio bands.
May we suggest you sprinkle some "Grow More fertilizer" around the base of your "chopped down satellite array" every Sunday morning and offer a few words of wisdom while so doing. With a little help and the dregs of Saturday night's Black and Tan, your mini array might grow.
Regards, Spectrum.
If you're going to post an ad, you should at least provide the proper contact info like web-site etc. so that we can take a look at your products - don't leave us hanging.
Jeff Moore -- KE7ACY CN94
----- Original Message ----- From: "Spectrum International, Inc" spectrum.ma.ultranet@rcn.com John, LA2QAA
That was an interesting message you posted to the -bb this morning. It has many true observations; however there is one serious mistake, an unforgivable error.
Quote: ......... particularly by the newcomers - who apparently, and mistakenly, think that high power is necessary. It's *NOT* . . . nor is an EME class aerial array necessary to work the LEO satellites. Ditto circular polarisation.
FACT: polarisation is *ONLY* circular along the boresight of an aerial.
Unquote. Your polarization statement is not 100% accurate. Unfortunately most antenna manufacturers, who supply/sell "alleged circular" polarized antennas do not state that their antennas are circular polarized ONLY along the boresight. They conveniently (?) do not mention that their alleged "circular polarized" antenna is only circular polarized on boresight, that it is linear polarized at 90 degrees off of boresight and is elliptical polarized of varying ratio at all angles in between!
There is however one (and only one that I am aware of) antenna design that is circular polarized over its entire radiation pattern. I refer you to the Q_uadrifilar Helix Antenna_ described by Dr. C.C.Kilgus in IEEE Trans., Vol. AP-16, July 1968, pp. 499-500. Also Bricker, R.W. and Rickert, H.H., in RCA Engineer, Vol.20, No. 5, February/March 1975. There is an excellent review by Walter Maxwell, W2DU, at http://www.IAG.net/~w2du/quadfinal.pdf.
When installed pointing to the zenith, the "ideal, theoretical" Quad Helix has 360 degree coverage in the azimuthal plane and 90 degree coverage in the elevation plane. It is circularly polarized over the entire upper hemisphere. There is no radiation in the lower hemi-sphere; the energy in the lower hemi-sphere of an isotropic radiator is uniformly distributed over the upper hemi-sphere. Hence the gain of an "ideal" Quad Helix is 3.01 dBi. However you can modify the elevation pattern to give more gain at the horizon and less gain overhead by adjustment of the overall length to diameter ratio. It is possible to adjust this ratio to give constant signal amplitude, at an earth based receiving station, from a satellite in a circular orbit where the range ratio (and hence signal path attenuation) between AOS and the zenith can be significant. This results in a little radiation below the horizon and also avoids the nasty mathematical boundary value problem at the horizon in the ideal case.
Quadrifilar Helix antennas are used on many LEO satellites for VHF, UHF, L-band and S-band communication. One of their parameters of interest to satellite builders is that they do NOT require a "ground plane" provided they are at least a quarter wavelength above the satellite structure. Hence there is negligible critical location requirement and they do not occupy satellite surface area that is required for solar cells.
The Quadrifilar Helix antenna is popular with earth based receiving stations for receiving the VHF image data signals from the NOAA weather satellites. Right-hand circular Quad Helix antennas for the 137MHz NOAA weather image signals and 137MHz left-hand circular Quad Helix antennas for receiving the ARGOS programme signals, are available from Spectrum International, Inc. Spectrum also supplies both right-hand and left-hand versions for the 2M and 70cm Amateur radio bands.
May we suggest you sprinkle some "Grow More fertilizer" around the base of your "chopped down satellite array" every Sunday morning and offer a few words of wisdom while so doing. With a little help and the dregs of Saturday night's Black and Tan, your mini array might grow.
Regards, Spectrum.
_______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
----- Original Message ----- From: "Spectrum International, Inc" spectrum.ma.ultranet@rcn.com To: "John Hackett_LA2QAA" archie.hackett@hotmail.com Cc: la2qaa@amsat.org; "AMSAT-BB" amsat-bb@amsat.org Sent: Wednesday, August 25, 2010 4:49 PM Subject: [amsat-bb] Circular Polarized Antennae
< Snip >
There is however one (and only one that I am aware of) antenna design that is circular polarized over its entire radiation pattern. I refer you to the Q_uadrifilar Helix Antenna_ described by Dr. C.C.Kilgus in IEEE Trans., Vol. AP-16, July 1968, pp. 499-500. Also Bricker, R.W. and Rickert, H.H., in RCA Engineer, Vol.20, No. 5, February/March 1975. There is an excellent review by Walter Maxwell, W2DU, at http://www.IAG.net/~w2du/quadfinal.pdf.
When installed pointing to the zenith, the "ideal,theoretical" Quad Helix has 360 degree coverage in the azimuthal plane and 90 degree coverage in the elevation plane. It is circularly polarized over the entire upper hemisphere. There is no radiation in the lower hemi-sphere; the energy in the lower hemi-sphere of an isotropic radiator is uniformly distributed over the upper hemi-sphere. Hence the gain of an "ideal" Quad Helix is 3.01 dBi. However you can modify the elevation pattern to give more gain at the horizon and less gain overhead by adjustment of the overall length to diameter ratio. It is possible to adjust this ratio to give constant signal amplitude, at an earth based receiving station, from a satellite in a circular orbit where the range ratio (and hence signal path attenuation) between AOS and the zenith can be significant. This results in a little radiation below the horizon and also avoids the nasty mathematical boundary value problem at the horizon in the ideal case.
Regards, Spectrum.
Hi Spectrum International,Inc
What you stated is absolutely correct and in my opinion the best comprehensive article written over the Quadrifilar Helix Antennas by Walter Maxell W2DU in his book "REFLECTIONS Transmission Lines and Antennas" is the following one:
Best 73" de
i8CVS Domenico
participants (3)
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i8cvs -
Jeff Moore -
Spectrum International, Inc