[amsat-bb] Re: Antenna Polarization
This is what I would recommend. I do not have polarization switching for either of my antennas. My 11 turn helix on 435 MHz is RHCP My 14 element KLM on 144 MHz is LHCP K9CIS has studied the polarizations of the uplink/downlink signals from AO-7, VO-52, and FO-29 and this seems to be the best selection. Using his recommendation, I do remember switching my KLM from RH to LH because AO7's downlink was weak and switching did solve the problem. The helix (polarization cannot be switched) was constructed for AO-40 (which was RH) and easily hears FO-29. The optimum set-up is to be able to switch polarization, but you know how things go in the world of ham radio. All the best. Mike (K9QHO) AMSAT 33589 ___ Sent via amsat...@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
[amsat-bb] Re: Antenna Polarization
- Original Message - From: "Patrick Domack" To: Sent: Wednesday, September 23, 2009 4:11 AM Subject: [amsat-bb] Antenna Polarization > I've been meaning to setup some antennas for satellite operation for > awhile here. And since I will probably end up doing it this > fall/winder I had a question I was wondering about, before I get the > antennas completely built connected up. > > I plan on using a circular polarized antenna, for lhcr and rhcr. > Since this setup has two coax that your switch a 1/4wave (if I > remember right) to either side to create the two rotations in the > antenna. > > Is there a way I can modify this to feed two radios? so one radio > would receive lhcr, and the other rhcr? Or would I be forced to use > two antennas to do this? > > The only idea I have is to use a signal splitter on each of the two > antenna halfs before joining them, then join each of those splits into > the cr parts. But I'm not sure if there is a better way to do this > without as much loss, or if this might cause a backfeed that would > defeat the me from getting any signal at all. > > Maybe there is a good writeup of this on the web somewhere, but I have > no clue what the proper terms to google it are, and haven't had any > luck. > > Thanks. > Hi Patrick What you propose to do is possible in theory but you need four 3 dB power dividers with characteristic impedance of 36 ohm each and 14 N/m male connectors so that the total losses of the system are too high. I suggest to switch from RHCP to LHCP over the same receiver using only a coax relay as described in all antenna books of the ARRL or into "The Satellite Experimenter's Handbook by Martin Davidoff K2UBC edited by the ARRL 73" de i8CVS Domenico ___ Sent via amsat...@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
[amsat-bb] Re: Antenna Polarization Question
I run linear polarization, and just live with the fades. Saves a lot of complexity and headaches! 73, Jim KQ6EA On 09/15/2012 06:47 PM, Thomas Doyle wrote: I was listening to a couple of guys on FO-29 having a nice chat about satellite antenna polarization. They were trying to figure out what type of polarization FO-29 used. They looked at the picture of FO-29 on the AMSAT web site and decided that it was not circular. Someone told me that it was circular so I started looking for information. Found this page by WD0E which is quite nice. http://www.amsat.org/amsat-new/information/faqs/pswitch.php Is there a more current page that contains this type of information. tnx W9KE Tom Doyle ___ 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 ___ 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
[amsat-bb] Re: Antenna Polarization Question
- Original Message - From: "Thomas Doyle" To: Sent: Saturday, September 15, 2012 8:47 PM Subject: [amsat-bb] Antenna Polarization Question > I was listening to a couple of guys on FO-29 having a nice chat about > satellite antenna polarization. They were trying to figure out what > type of polarization FO-29 used. They looked at the picture of FO-29 > on the AMSAT web site and decided that it was not circular. Someone > told me that it was circular so I started looking for information. > Found this page by WD0E which is quite nice. > > http://www.amsat.org/amsat-new/information/faqs/pswitch.php > > Is there a more current page that contains this type of information. > > tnx W9KE Tom Doyle Hi Tom, W9KE For the antenna polarization of FO-29 please read belove: --- AMSAT NEWS SERVICE BULLETIN 254.S1 FROM AMSAT HQ SILVER SPRING, MD, September 10, 2012 TO ALL RADIO AMATEURS BID: $WSR-254.S1 FO-29 JAS-2 Catalog number: 24278 Launch Date: August 17, 1996 Mode and Antenna Polarization: V: RHCP U: RHCP i8CVS Note: Following my experience on FO-29 I can add the information belowe: FO-29 is RHCP circularly polarized both in uplink and downlink and has a fixed sense both up and down, but because of its orbit geometry and motion, continuously good signals through it for an entire pass can only maintained if the antennas ground station sense is switched, RHCP to LHCP and vice versa in 70 cm and 2 meters usually several times and on both uplink and downlink and so polarization switching relays on board of both up and down antennas are recommended. Read please my articles about polarization switching published on the AMSAT-Journal March/April 2007 and May/June 2007 73" de i8CVS Domenico ___ 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
[amsat-bb] Re: Antenna Polarization Question
Domenico, Thanks for the reply. I am slowly building my sat station back to what it was back in the day when I had a pair of KLM antennas with polarization switching. I have recently added a switchable polarization 70 cm antenna to my current station and am amazed at how often during an FO-29 pass it is necessary to change polarization. My memory is not what it should be but I do not remember as much switching being necessary when using AO-10 era sats. Perhaps they were more stable or the pass was so long that it did not seem like it required as much switching. "In 1911, Albert Abraham Michelson discovered that light reflected from the golden scarab beetle Chrysina resplendens is preferentially left-handed." After reading this I wondered if it is possible to create a reflector for RF that would do something similar to what this tiny insect does without even trying. When I asked how to change the polarization sense of a lindenblad antenna I was going to build the author of the article told me that it was not necessary to switch it because there were so many reflections it would not matter. Perhaps a controlled reflective surface would work. tnx & 73 W9KE Tom Doyle On Sat, Sep 15, 2012 at 3:00 PM, i8cvs wrote: > - Original Message - > From: "Thomas Doyle" > To: > Sent: Saturday, September 15, 2012 8:47 PM > Subject: [amsat-bb] Antenna Polarization Question > >> I was listening to a couple of guys on FO-29 having a nice chat about >> satellite antenna polarization. They were trying to figure out what >> type of polarization FO-29 used. They looked at the picture of FO-29 >> on the AMSAT web site and decided that it was not circular. Someone >> told me that it was circular so I started looking for information. >> Found this page by WD0E which is quite nice. >> >> http://www.amsat.org/amsat-new/information/faqs/pswitch.php >> >> Is there a more current page that contains this type of information. >> >> tnx W9KE Tom Doyle > > Hi Tom, W9KE > > For the antenna polarization of FO-29 please read belove: > --- > AMSAT NEWS SERVICE BULLETIN 254.S1 > FROM AMSAT HQ SILVER SPRING, MD, September 10, 2012 > TO ALL RADIO AMATEURS > BID: $WSR-254.S1 > > FO-29 JAS-2 > Catalog number: 24278 > Launch Date: August 17, 1996 > > Mode and Antenna Polarization: > V: RHCP > U: RHCP > > i8CVS Note: > > Following my experience on FO-29 I can add the information > belowe: > > FO-29 is RHCP circularly polarized both in uplink and downlink > and has a fixed sense both up and down, but because of its orbit > geometry and motion, continuously good signals through it for an > entire pass can only maintained if the antennas ground station sense > is switched, RHCP to LHCP and vice versa in 70 cm and 2 meters > usually several times and on both uplink and downlink and so > polarization switching relays on board of both up and down antennas > are recommended. > > Read please my articles about polarization switching published on > the AMSAT-Journal March/April 2007 and May/June 2007 > > 73" de > > i8CVS Domenico > -- Sent from my computer. tom ... ___ 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
[amsat-bb] Re: Antenna Polarization Question
- Original Message - From: "Thomas Doyle" To: "i8cvs" Cc: "Amsat - BBs" Sent: Saturday, September 15, 2012 10:34 PM Subject: Re: [amsat-bb] Antenna Polarization Question > Domenico, > > Thanks for the reply. I am slowly building my sat station back to what > it was back in the day when I had a pair of KLM antennas with > polarization switching. I have recently added a switchable > polarization 70 cm antenna to my current station and am amazed at how > often during an FO-29 pass it is necessary to change polarization. My > memory is not what it should be but I do not remember as much > switching being necessary when using AO-10 era sats. Perhaps they were > more stable or the pass was so long that it did not seem like it > required as much switching. > < snip > > > tnx & 73 W9KE Tom Doyle > Hi Tom, W9KE Using AO-10 and in general HEO satellites like AO-13 and AO40 switching polarization was less necessary than using LEO satellites because most of the time the satellite antennas were oriented toward the earth with a small squint angle so that the polarization changed very slowly mostly due only to the Faraday polarization rotation when the wave passed through the ionosphere. BTW the above HEO satellites were spinning over the Z axis generating the so called "spin modulation" wich sounded like WOW...WOW.WOW.WOW Only the AO40 downlink at 2401 MHz was less affected by the polarization rotation due to Faraday effect and less affected by the spin modulation. Hope that some time in the future the HEO satellite P3E will be placed in orbit ! 73" de i8CVS Domenico ___ 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
[amsat-bb] Re: Antenna Polarization Technical Question
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 wrote: > > Hi Tom, > >I thought fo-29 was transmitting circular. Would not surprise me if I was > wrong:) > > Andy, >kn6za > > ___ > 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 -- Sent from my computer. tom ... ___ 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
[amsat-bb] Re: Antenna Polarization Technical Question
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: tomdoyle1...@gmail.com > To: kn...@hotmail.com > CC: amsat-bb@amsat.org > > 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 wrote: > > > > Hi Tom, > > > >I thought fo-29 was transmitting circular. Would not surprise me if I > > was wrong:) > > > > Andy, > >kn6za > > > > ___ > > 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 > > > > -- > > Sent from my computer. > > tom ... ___ 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
[amsat-bb] Re: Antenna Polarization Technical Question
> 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 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
[amsat-bb] Re: Antenna Polarization Technical Question
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 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 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
[amsat-bb] Re: Antenna Polarization Technical Question
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 wrote: Hi Tom, I thought fo-29 was transmitting circular. Would not surprise me if I was wrong:) Andy, kn6za ___ 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 ___ 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
[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 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
[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. There are two perspectives in answering this. 1. You used the word "maintain," which implies the ability of the spacecraft to control its attitude. That's commonly done for commercial and military satellites, but rarely (if ever) done for amateur satellites. It's just too complicated and too expensive for amateurs to allocate the resources to make it happen. 2. You also asked why anyone would WANT to maintain the orientation like that. In a more general sense, recognize that not every satellite is a communications satellite, supporting communications with terrestrial stations. Scientific missions often have to point a body-mounted sensor somewhere, and the comm payload has to "adjust." For example, Hubble's main body IS the telescope, so it MUST point at the astronomical targets. For that mission, NASA paid for an articulated communications payload, but spacecraft don't always do that. 73, Steve W3HF ___ 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
[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 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 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
[amsat-bb] Re: Antenna Polarization Technical Question
Hi Thomas, W9KE In a separate email I have sent to you a very compreensive article explaining why during an orbit of a LEO satellite like FO-29 the changes in polarization is generated. 73" de i8CVS Domenico - Original Message - From: "Thomas Doyle" To: Sent: Saturday, August 04, 2012 4:46 PM Subject: [amsat-bb] Antenna Polarization Technical Question > I had a actual qso on FO-29 the other day and during the contact > circular polarization switching was discussed. > The station I was talking with described a very large change in > received signal strength when switching > between LHCP and RHCP. I have heard other people mention this and I > recall some change when using > AO-10 with my switchable KLM's back in the good old days. > > I have been trying to figure out why there would be such a big change. > Here is a collection of theories/questions. > I would appreciate comments on any or all of them. This is a bit > complex so a direct reply is probably best. > > - In a perfect world if the satellite antenna is linearly polarized > LH-RH switching would not make any difference. > > - In a real world it is unlikely that the ground station receive > antenna is truly circular. It is somewhat elliptical. > > Question: if the receive antenna has an elliptical pattern does the > angle of the major axis change when > switching LH - RH. > This is a complex question related to the nature of what caused the > elliptical distortion in the pattern. > Perhaps someone has measured this. If the angle of the major axis > receive antenna pattern changes when > switching between LH and RH and the satellite antenna is linearly > polarized this could account for some change > in received signal strength. Other than that I am at a loss to explain > why switching LH-RH on a receive antenna > would cause a large change in the strength of a signal received from a > linear antenna. > > > tnx & 73 W9KE Tom Doyle > ___ > 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 ___ 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
[amsat-bb] Re: Antenna Polarization Technical Question
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" To: ; 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 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 ___ 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
[amsat-bb] Re: Antenna Polarization Technical Question
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 " To: "Thomas Doyle" Cc: ; "andrew abken" 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 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 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 ___ 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
[amsat-bb] Re: Antenna Polarization Technical Question
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 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 " > To: "Thomas Doyle" > Cc: ; "andrew abken" > 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 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 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 > -- Sent from my computer. tom ... ___ 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
[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: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Bob Bruninga Sent: Saturday, August 04, 2012 3:25 PM To: Thomas Doyle Cc: amsat-bb@amsat.org; 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 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 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 ___ 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
[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" To: "'Bob Bruninga '" ; "'Thomas Doyle'" Cc: ; "'andrew abken'" 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: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On > Behalf Of Bob Bruninga > Sent: Saturday, August 04, 2012 3:25 PM > To: Thomas Doyle > Cc: amsat-bb@amsat.org; 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 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 AMSAT-BB@amsat.org. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subsc
[amsat-bb] Re: Antenna Polarization Technical Question
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:domenico.i8...@tin.it] Sent: Sunday, August 05, 2012 3:27 PM To: AMSAT-BB; Bob Bruninga ; kc6...@cox.net; 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" To: "'Bob Bruninga '" ; "'Thomas Doyle'" Cc: ; "'andrew abken'" 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: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On > Behalf Of Bob Bruninga > Sent: Saturday, August 04, 2012 3:25 PM > To: Thomas Doyle > Cc: amsat-bb@amsat.org; 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
