Today I built and compared two 70 cm antennae against various satellites.
The first antenna was a RHCP helix with 9 turns
The second antenna, a 8 element quagi. (vertically)
The clear winner was the helix.
Anyone had similar experiences ?
I remember way back about 10 years ago, i built a quad with a metal boom, and it picked up better side on. (not good)
I have kept to an 8 element quad on 2meters, it is really good.
I can key up a repeater some 150 km's away and i am in a ditch.
---------------------------------------------------------------------------- Andrew Rich VK4TEC vk4tec@people.net.au http://www.tech-software.net
Andrew, Helix antennas being circulary polorized have rejection to the opposite rotation generaly caused by reflections provided that both sides are of the same circular polorization. Reflections from buildings etc can cause signal cancelation as well as combining reflections as the satillite moves overhead. In addition the satellite spin does not effect the signal strength on a circularized antenna even if the satellite uses a linear antenna.
When the satellite is at low elevation the linear antenna may work quite well as there ae few strong reflections. This assumes the you are tracking the satellite with both antennas during the pass. If the satellite is antenna is pointing away from you the rotation polarity is reversed causing you not to receive the satellite or hear it very weakly. Then the Vertical antenna will work better than the Helix. Art, KC6UQH
----- Original Message ----- From: "Andrew Rich" vk4tec@people.net.au To: "Amsat-Bb@Amsat. Org" amsat-bb@amsat.org Cc: "Aprssig" aprssig@lists.tapr.org; "ozaprs" ozaprs@aprs.net.au Sent: Friday, December 07, 2007 1:51 AM Subject: [amsat-bb] QUAGI vs HELIX vs QUAD
Today I built and compared two 70 cm antennae against various satellites.
The first antenna was a RHCP helix with 9 turns
The second antenna, a 8 element quagi. (vertically)
The clear winner was the helix.
Anyone had similar experiences ?
I remember way back about 10 years ago, i built a quad with a metal boom, and it picked up better side on. (not good)
I have kept to an 8 element quad on 2meters, it is really good.
I can key up a repeater some 150 km's away and i am in a ditch.
Andrew Rich VK4TEC vk4tec@people.net.au http://www.tech-software.net
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
Helix antennas being circulary polorized have rejection to the opposite rotation generaly caused by reflections provided that both...
Wow, interesting. I just realized then, that the "reflector screen" at the back of a Helix is not adding any gain then. Because it is true, that any reflected energy will be the opposite circularity! Thus it cannot add in phase to the direct wave.
I guess all the ground plane is doing is providing a counterpoise for the feed system. Oh, and possibly a degree of attenuation to ground noise... Both well worth the metal, I guess. Comments?
Bob, WB4APR
Bob, The bottom side of the helix is the opposite rotation, the screen as you pointed out is a counterpoise that determines the driving end and the radiating end. I have also phased two helixes one LH and one RH for linear polorization. You can get more gain than a yagi at 1.2 GHz using this configuration. 3 db for phasing + 3 dB recovered for linear.
Art, KC6UQH ----- Original Message ----- From: "Robert Bruninga" bruninga@usna.edu To: "'kc6uqh'" kc6uqh@cox.net; vk4tec@people.net.au; "'Amsat-Bb@Amsat. Org'" amsat-bb@amsat.org Cc: "'Aprssig'" aprssig@lists.tapr.org; "'ozaprs'" ozaprs@aprs.net.au Sent: Tuesday, December 11, 2007 3:49 PM Subject: Helix Groundplane?
Helix antennas being circulary polorized have rejection to the opposite rotation generaly caused by reflections provided that both...
Wow, interesting. I just realized then, that the "reflector screen" at the back of a Helix is not adding any gain then. Because it is true, that any reflected energy will be the opposite circularity! Thus it cannot add in phase to the direct wave.
I guess all the ground plane is doing is providing a counterpoise for the feed system. Oh, and possibly a degree of attenuation to ground noise... Both well worth the metal, I guess. Comments?
Bob, WB4APR
But since you are looking at the signal from the other side (the back) of the helix, the circular polarisation appears reversed. Reflecting it changes this so that it is in phase.
Think of a clock, built from invisible materials except for the hands. If you stand in front of it, the hands rotate clockwise. Stand behind it and they appear to be turn anticlockwise. Look at the rear that is reflected in a mirror and they moving clockwise again.
Now, imagine that radio wave coming towards you....
So, positioned correctly, a reflector behind a helix will add to it's gain and reduce the beamwidth, won't it?
Sil ZL2CIA
Robert Bruninga wrote:
Helix antennas being circulary polorized have rejection to the opposite rotation generaly caused by reflections provided that both...
Wow, interesting. I just realized then, that the "reflector screen" at the back of a Helix is not adding any gain then. Because it is true, that any reflected energy will be the opposite circularity! Thus it cannot add in phase to the direct wave.
I guess all the ground plane is doing is providing a counterpoise for the feed system. Oh, and possibly a degree of attenuation to ground noise... Both well worth the metal, I guess. Comments?
Bob, WB4APR
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
participants (4)
-
Andrew Rich -
kc6uqh -
Robert Bruninga -
Sil - ZL2CIA