Antenna Polarization Technical Question
Hi Tom,
I thought fo-29 was transmitting circular. Would not surprise me if I was wrong:)
Andy, kn6za
Andy,
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass. Perhaps there is some sort of Faraday Rotation effect but I do not believe that it can change the direction of the circular polarized signal but who knows what magic things happen in the ether.
tnx & 73 W9KE Tom Doyle
On Sat, Aug 4, 2012 at 12:44 PM, andrew abken [email protected] wrote:
Hi Tom,
I thought fo-29 was transmitting circular. Would not surprise me if I was wrong:)
Andy, kn6za
Sent via [email protected]. 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
Hi Tom,
I have also noticed the switching of polarity as the sat travels over.
What I have understood to be the mode by which this is occuring comes from the fact that circular polarized antennas change polarity as you move out of the main radiation lobe. The main lobe is circular one direction and the next lobe is reversed, and the next reversed back again.
Hope someone can correct me if I have things fouled up.
Andy
Date: Sat, 4 Aug 2012 14:13:47 -0500 Subject: Re: [amsat-bb] Antenna Polarization Technical Question From: [email protected] To: [email protected] CC: [email protected]
Andy,
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass. Perhaps there is some sort of Faraday Rotation effect but I do not believe that it can change the direction of the circular polarized signal but who knows what magic things happen in the ether.
tnx & 73 W9KE Tom Doyle
On Sat, Aug 4, 2012 at 12:44 PM, andrew abken [email protected] wrote:
Hi Tom,
I thought fo-29 was transmitting circular. Would not surprise me if I was wrong:)
Andy, kn6za
Sent via [email protected]. 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
--
Sent from my computer.
tom ...
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all you can get on a spacecraft) May be designed for Right hand circularity when viewed from the prime direction. But by definition, that save waveform will be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR
Bob,
Thanks for the reply. A student of mine once told me that if someone tells you something is easy - it is not. Even though this is not only easy but "very easy" I still need a slight clarification. I think it boils down to the orientation of the satellite relative to the center of the earth.
If the satellite was a clock and the face of the clock was oriented toward the center of the earth the I believe the clock would appear to rotate CW on both ends of the pass. If the side of the clock rather than the face of the clock was oriented toward the center of the earth it would appear to rotate one way at the start of the pass and the other way at the end of the pass because we would be looking at the clock from the other side. I believe this is the basis of the "very easy" explanation you offered.
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path. Perhaps people selling antenna circularity switches would like it but other than that I do not understand why it would be done. I am most likely missing something important.
tnx & 73 W9KE Tom Doyle
On Sat, Aug 4, 2012 at 2:47 PM, Bob Bruninga [email protected] wrote:
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all you can get on a spacecraft) May be designed for Right hand circularity when viewed from the prime direction. But by definition, that save waveform will be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR
Tom,
I don't think any one who designs a system "wants" this to occur, but as a function of overall system cost it is one of the unavoidable realities.
Its actually a great compromise, because with only a 3db loss you can use a linear rec. antenna with no polarity switching, and avoid the large fading that would occur if the satellite was transmitting linear.
Now if you have the money to build a satellite that can point itself at the receiving station at all times ie: geo synchronous:)$$$$ then that would be the cats meow;)
73 Andy
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path. Perhaps people selling antenna circularity switches would like it but other than that I do not understand why it would be done. I am most likely missing something important.
Hi Tom, KN6ZA
With only a 3db loss you can use a linear rec. antenna with no polarity switching, and avoid the large fading that would occur if the satellite was transmitting circular RHCP or LHCP........(but not linear as you stated)
On the other side if you receive linear and the satellite transmit linearly with opposite polarity you get more than 20dB of fading.
73" de
i8CVS Domenico
----- Original Message ----- From: "andrew abken" [email protected] To: [email protected]; [email protected] Sent: Saturday, August 04, 2012 10:45 PM Subject: [amsat-bb] Re: Antenna Polarization Technical Question
Tom,
I don't think any one who designs a system "wants" this to occur, but
as a function of overall system cost it is one of the unavoidable realities.
Its actually a great compromise, because with only a 3db loss you can
use a linear rec. antenna with no polarity switching, and avoid the large fading that would occur if the satellite was transmitting linear.
Now if you have the money to build a satellite that can point itself at
the receiving station at all times ie: geo synchronous:)$$$$ then that would be the cats meow;)
73 Andy
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path. Perhaps people selling antenna circularity switches would like it but other than that I do not understand why it would be done. I am most likely missing something important.
Sent via [email protected]. 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
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path.
Lets try this approach... As I said before, By the laws of physics, what comes out one side of a circular polarized low gain antenna as RHCP comes out the opposite side as LHCP.
Now given that, and the fact that someone in Maryland is in the center of the RHCP beam, then by the laws of physics, the guy in California must see mostly LHCP. No matter how much one of those persons demands that he deserves the RHCP beam, by definition, someone else somewhere will get the LHCP one, and the geometry changes at least every 10 minutes or so and every time the spacecraft rotates a bit.
So one might say, "point it down" then only the person in Kansas will see the main beam and those in CA or MD will be completely off the sides almost 70 degrees from the main beam. Mot people do not realize how LOW these satellites are. The only solution is to put satellites so high, that "down" is about the same to everyone (geostationary altitude). But then that takes 100 times more altitude, and that takes 10,000 times more power.
Better to just live with the laws of physics... I guess.
Bob, WB4aPR
On Sat, Aug 4, 2012 at 2:47 PM, Bob Bruninga [email protected] wrote:
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all you can get on a spacecraft) May be designed for Right hand circularity when viewed from the prime direction. But by definition, that save waveform will be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR
--
Sent from my computer.
tom ...
Hi All,
I agree completely with Bob, WB4APR and this is what is wery well explained into the article "CIRCULAR POLARIZATION by K4KJ, a zipped file 5 MB long available from me.
73" de
i8CVS Domenico
----- Original Message ----- From: "Bob Bruninga " [email protected] To: "Thomas Doyle" [email protected] Cc: [email protected]; "andrew abken" [email protected] Sent: Sunday, August 05, 2012 12:24 AM Subject: [amsat-bb] Re: Antenna Polarization Technical Question
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path.
Lets try this approach... As I said before, By the laws of physics, what
comes out one side of a circular polarized low gain antenna as RHCP comes out the opposite side as LHCP.
Now given that, and the fact that someone in Maryland is in the center of
the RHCP beam, then by the laws of physics, the guy in California must see mostly LHCP. No matter how much one of those persons demands that he deserves the RHCP beam, by definition, someone else somewhere will get the LHCP one, and the geometry changes at least every 10 minutes or so and every time the spacecraft rotates a bit.
So one might say, "point it down" then only the person in Kansas will see
the main beam and those in CA or MD will be completely off the sides almost 70 degrees from the main beam. Mot people do not realize how LOW these satellites are. The only solution is to put satellites so high, that "down" is about the same to everyone (geostationary altitude). But then that takes 100 times more altitude, and that takes 10,000 times more power.
Better to just live with the laws of physics... I guess.
Bob, WB4aPR
On Sat, Aug 4, 2012 at 2:47 PM, Bob Bruninga [email protected] wrote:
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all
you can get on a spacecraft) May be designed for Right hand circularity when viewed from the prime direction. But by definition, that save waveform will be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by
almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR
--
Sent from my computer.
tom ...
Sent via [email protected]. 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
Thanks to Domenico for sharing the work done by K4KJ. It is amazing how much good information there is out there. It takes a bit of digging to find it but it is worth the effort. The configuration shown in figure 14 looks promising but probably too difficult to put on a sat.
W9KE Tom Doyle
On Sat, Aug 4, 2012 at 10:18 PM, i8cvs [email protected] wrote:
Hi All,
I agree completely with Bob, WB4APR and this is what is wery well explained into the article "CIRCULAR POLARIZATION by K4KJ, a zipped file 5 MB long available from me.
73" de
i8CVS Domenico
----- Original Message ----- From: "Bob Bruninga " [email protected] To: "Thomas Doyle" [email protected] Cc: [email protected]; "andrew abken" [email protected] Sent: Sunday, August 05, 2012 12:24 AM Subject: [amsat-bb] Re: Antenna Polarization Technical Question
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path.
Lets try this approach... As I said before, By the laws of physics, what
comes out one side of a circular polarized low gain antenna as RHCP comes out the opposite side as LHCP.
Now given that, and the fact that someone in Maryland is in the center of
the RHCP beam, then by the laws of physics, the guy in California must see mostly LHCP. No matter how much one of those persons demands that he deserves the RHCP beam, by definition, someone else somewhere will get the LHCP one, and the geometry changes at least every 10 minutes or so and every time the spacecraft rotates a bit.
So one might say, "point it down" then only the person in Kansas will see
the main beam and those in CA or MD will be completely off the sides almost 70 degrees from the main beam. Mot people do not realize how LOW these satellites are. The only solution is to put satellites so high, that "down" is about the same to everyone (geostationary altitude). But then that takes 100 times more altitude, and that takes 10,000 times more power.
Better to just live with the laws of physics... I guess.
Bob, WB4aPR
On Sat, Aug 4, 2012 at 2:47 PM, Bob Bruninga [email protected] wrote:
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all
you can get on a spacecraft) May be designed for Right hand circularity when viewed from the prime direction. But by definition, that save waveform will be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by
almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR
--
Sent from my computer.
tom ...
Sent via [email protected]. 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
Bob, Just a reminder, a QFH antenna is circularly polarized over the whole envelope of the antenna. A sharp null exists on the back side. A one wavelength, one turn has gain at low angle side radiation and a 4 dB loss overhead, where the distance to the ground station is the smallest. Certainly this is a good fit for satellites.
Turnstile antennas and patch antennas are linear polarized at the sides and of course are the easiest to implement on a satellite.
My point is all circular antennas are not equal and having an antenna with gain on the sides opposed to the center of the antenna is very desirable.
Art, KC6UQH
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bob Bruninga Sent: Saturday, August 04, 2012 3:25 PM To: Thomas Doyle Cc: [email protected]; andrew abken Subject: [amsat-bb] Re: Antenna Polarization Technical Question
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path.
Lets try this approach... As I said before, By the laws of physics, what comes out one side of a circular polarized low gain antenna as RHCP comes out the opposite side as LHCP.
Now given that, and the fact that someone in Maryland is in the center of the RHCP beam, then by the laws of physics, the guy in California must see mostly LHCP. No matter how much one of those persons demands that he deserves the RHCP beam, by definition, someone else somewhere will get the LHCP one, and the geometry changes at least every 10 minutes or so and every time the spacecraft rotates a bit.
So one might say, "point it down" then only the person in Kansas will see the main beam and those in CA or MD will be completely off the sides almost 70 degrees from the main beam. Mot people do not realize how LOW these satellites are. The only solution is to put satellites so high, that "down" is about the same to everyone (geostationary altitude). But then that takes 100 times more altitude, and that takes 10,000 times more power.
Better to just live with the laws of physics... I guess.
Bob, WB4aPR
On Sat, Aug 4, 2012 at 2:47 PM, Bob Bruninga [email protected] wrote:
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all
you can get on a spacecraft) May be designed for Right hand circularity when viewed from the prime direction. But by definition, that save waveform will be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by
almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR
--
Sent from my computer.
tom ...
_______________________________________________ Sent via [email protected]. 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
Hi Art, KC6UQH
It is correct that a QFH is circularly polarized over the whole envelope of the antenna.If it is left wound the polarization is RHCP and if it is right wound the resulting polarization is LHCP.
By the way the point is the satellite antenna.
If the satellite antenna is made using two crossed dipoles mounted in the same mechanical plane and are supplied with 90° out of phase than the radiated polarization is RHCP along one axial direction and LHCP along the other axial direction.
Since the satellite is thumbling orbiting in the space than the polarization coming from the satellite to earth or coming from the ground station to the satellite is continuing changing from RHCP to LHCP to linear passing through elliptical.
The bad point is that a QFH can only radiate RHCP or LHCP depending on it's winding direction so that using only one QFH the QSB generated by the satellite thumbling cannot be completely eliminated and two switchable QFH's one RHCP and the other one LHCP would be necessary.
73" de
i8CVS Domenico
----- Original Message ----- From: "Art McBride" [email protected] To: "'Bob Bruninga '" [email protected]; "'Thomas Doyle'" [email protected] Cc: [email protected]; "'andrew abken'" [email protected] Sent: Sunday, August 05, 2012 10:44 PM Subject: [amsat-bb] Re: Antenna Polarization Technical Question
Bob, Just a reminder, a QFH antenna is circularly polarized over the whole envelope of the antenna. A sharp null exists on the back side. A one wavelength, one turn has gain at low angle side radiation and a 4 dB loss overhead, where the distance to the ground station is the smallest. Certainly this is a good fit for satellites.
Turnstile antennas and patch antennas are linear polarized at the sides
and
of course are the easiest to implement on a satellite.
My point is all circular antennas are not equal and having an antenna with gain on the sides opposed to the center of the antenna is very desirable.
Art, KC6UQH
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bob Bruninga Sent: Saturday, August 04, 2012 3:25 PM To: Thomas Doyle Cc: [email protected]; andrew abken Subject: [amsat-bb] Re: Antenna Polarization Technical Question
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path.
Lets try this approach... As I said before, By the laws of physics, what comes out one side of a circular polarized low gain antenna as RHCP comes out the opposite side as LHCP.
Now given that, and the fact that someone in Maryland is in the center of the RHCP beam, then by the laws of physics, the guy in California must see mostly LHCP. No matter how much one of those persons demands that he deserves the RHCP beam, by definition, someone else somewhere will get the LHCP one, and the geometry changes at least every 10 minutes or so and
every
time the spacecraft rotates a bit.
So one might say, "point it down" then only the person in Kansas will see the main beam and those in CA or MD will be completely off the sides
almost
70 degrees from the main beam. Mot people do not realize how LOW these satellites are. The only solution is to put satellites so high, that
"down"
is about the same to everyone (geostationary altitude). But then that
takes
100 times more altitude, and that takes 10,000 times more power.
Better to just live with the laws of physics... I guess.
Bob, WB4aPR
On Sat, Aug 4, 2012 at 2:47 PM, Bob Bruninga [email protected] wrote:
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all
you can get on a spacecraft) May be designed for Right hand circularity
when
viewed from the prime direction. But by definition, that save waveform
will
be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by
almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR
--
Sent from my computer.
tom ...
Sent via [email protected]. 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
Sent via [email protected]. 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
Domenico,
You are correct, the crossed dipoles fed in quadrature when on axis exhibit LH and RH circular patterns, but 90 degrees from axis they are linearly polarized. This gives poor performance at low angles as well as requiring both RH and LH rotations for a full pass reception.
Obviously the QFH antenna to be effective should point down at the earth, with the sides pointing to the horizon and the backside towards outer space. The one wave one turn can be optimized,(Length to Diameter ratio)to provide best radiation at the horizon. This will give good performance when the satellite is near zenith as well as provide improved performance at low elevations.
Circular polarization does help to eliminate multipath and provide a steady copy, even while the antenna is mechanically rotating with the satellite for stabilization and temperature stability.
Art, KC6UQH
-----Original Message----- From: i8cvs [mailto:[email protected]] Sent: Sunday, August 05, 2012 3:27 PM To: AMSAT-BB; Bob Bruninga ; [email protected]; Thomas Doyle Subject: Re: [amsat-bb] Re: Antenna Polarization Technical Question
Hi Art, KC6UQH
It is correct that a QFH is circularly polarized over the whole envelope of the antenna.If it is left wound the polarization is RHCP and if it is right wound the resulting polarization is LHCP.
By the way the point is the satellite antenna.
If the satellite antenna is made using two crossed dipoles mounted in the same mechanical plane and are supplied with 90° out of phase than the radiated polarization is RHCP along one axial direction and LHCP along the other axial direction.
Since the satellite is thumbling orbiting in the space than the polarization coming from the satellite to earth or coming from the ground station to the satellite is continuing changing from RHCP to LHCP to linear passing through elliptical.
The bad point is that a QFH can only radiate RHCP or LHCP depending on it's winding direction so that using only one QFH the QSB generated by the satellite thumbling cannot be completely eliminated and two switchable QFH's one RHCP and the other one LHCP would be necessary.
73" de
i8CVS Domenico
----- Original Message ----- From: "Art McBride" [email protected] To: "'Bob Bruninga '" [email protected]; "'Thomas Doyle'" [email protected] Cc: [email protected]; "'andrew abken'" [email protected] Sent: Sunday, August 05, 2012 10:44 PM Subject: [amsat-bb] Re: Antenna Polarization Technical Question
Bob, Just a reminder, a QFH antenna is circularly polarized over the whole envelope of the antenna. A sharp null exists on the back side. A one wavelength, one turn has gain at low angle side radiation and a 4 dB loss overhead, where the distance to the ground station is the smallest. Certainly this is a good fit for satellites.
Turnstile antennas and patch antennas are linear polarized at the sides
and
of course are the easiest to implement on a satellite.
My point is all circular antennas are not equal and having an antenna with gain on the sides opposed to the center of the antenna is very desirable.
Art, KC6UQH
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bob Bruninga Sent: Saturday, August 04, 2012 3:25 PM To: Thomas Doyle Cc: [email protected]; andrew abken Subject: [amsat-bb] Re: Antenna Polarization Technical Question
Not sure why anyone would want to maintain the orientation of the satellite in such a way that would cause the direction of circular polarization to change during the path.
Lets try this approach... As I said before, By the laws of physics, what comes out one side of a circular polarized low gain antenna as RHCP comes out the opposite side as LHCP.
Now given that, and the fact that someone in Maryland is in the center of the RHCP beam, then by the laws of physics, the guy in California must see mostly LHCP. No matter how much one of those persons demands that he deserves the RHCP beam, by definition, someone else somewhere will get the LHCP one, and the geometry changes at least every 10 minutes or so and
every
time the spacecraft rotates a bit.
So one might say, "point it down" then only the person in Kansas will see the main beam and those in CA or MD will be completely off the sides
almost
70 degrees from the main beam. Mot people do not realize how LOW these satellites are. The only solution is to put satellites so high, that
"down"
is about the same to everyone (geostationary altitude). But then that
takes
100 times more altitude, and that takes 10,000 times more power.
Better to just live with the laws of physics... I guess.
Bob, WB4aPR
On Sat, Aug 4, 2012 at 2:47 PM, Bob Bruninga [email protected] wrote:
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all
you can get on a spacecraft) May be designed for Right hand circularity
when
viewed from the prime direction. But by definition, that save waveform
will
be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by
almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR
--
Sent from my computer.
tom ...
Sent via [email protected]. 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
Sent via [email protected]. 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
I can't explain it but have noticed the same polarity changes during a pass. Like S-9 to S-1/nothing switching between polarities with my antennas... it's been handy to actually have the ability to change polarities in the past for me. I do not have the ability to polarity switch on 2 meters, only 70 cM for the downlink.
73,
Bob W1ICW
On 8/4/2012 3:13 PM, Thomas Doyle wrote:
Andy,
I believe that is true but that does not explain why the optimum polarity setting on the receive end would change during a pass. Perhaps there is some sort of Faraday Rotation effect but I do not believe that it can change the direction of the circular polarized signal but who knows what magic things happen in the ether.
tnx & 73 W9KE Tom Doyle
On Sat, Aug 4, 2012 at 12:44 PM, andrew abken [email protected] wrote:
Hi Tom,
I thought fo-29 was transmitting circular. Would not surprise me if I was wrong:)Andy, kn6za
Sent via [email protected]. 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 (6)
-
andrew abken -
Art McBride -
Bob Bruninga -
Bob DeVarney W1ICW -
i8cvs -
Thomas Doyle