[amsat-bb] Re: STRaND1 polarity shift observation
Hi Ken, W7KKE The answere to your question is clearly described into the zipped article "Circular Polarization" by K4KJ, 5 MB long that I have sent to you in a separate email. 73" de i8CVS Domenico - Original Message - From: "Ken Swaggart" To: Sent: Monday, March 04, 2013 5:10 AM Subject: [amsat-bb] STRaND1 polarity shift observation > During my last pass at 0332Z, max elevation 45 degrees out over the Pacific, > I noticed that STRaND1 was stronger when I selected LHCP while approaching > TCA. After TCA, RHCP was stronger while it was receding. I believe this > cubesat uses a whip, so not sure what is causing this. > > Anyone have an idea why? > > Tnx, > Ken, W7KKE > CN75xa > > > ___ > 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: STRaND1 polarity shift observation
Domenico, Thanks for sending the K4KJ article. However my question was why does STRaND1, which only has a whip antenna, sometimes appear to exhibit circular polarity characteristics? I would expect a whip antenna transmitting from space to have the same signal strength on the ground using either RH or LH polarity on my receiving antenna. 73, Ken, W7KKE -Original Message- From: i8cvs Sent: Monday, March 04, 2013 00:42 To: Ken Swaggart ; Amsat - BBs Subject: Re: [amsat-bb] STRaND1 polarity shift observation Hi Ken, W7KKE The answere to your question is clearly described into the zipped article "Circular Polarization" by K4KJ, 5 MB long that I have sent to you in a separate email. 73" de i8CVS Domenico - Original Message - From: "Ken Swaggart" To: Sent: Monday, March 04, 2013 5:10 AM Subject: [amsat-bb] STRaND1 polarity shift observation During my last pass at 0332Z, max elevation 45 degrees out over the Pacific, I noticed that STRaND1 was stronger when I selected LHCP while approaching TCA. After TCA, RHCP was stronger while it was receding. I believe this cubesat uses a whip, so not sure what is causing this. Anyone have an idea why? Tnx, Ken, W7KKE CN75xa ___ 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: STRaND1 polarity shift observation
Hi Ken, You can experience the same effect from SO-50 when using circularly polarized antennas on ground. SO-50 also have linear antennas for the FM repeater. I must change between RHCP and LHCP to get maximum signal during a pass. Sometimes the difference is from zero to a very good signal. I think it is interaction between the antennas and the rest of the structure of the satellite combined with the passive attitude control and the angle you see the satellite in. 73 OZ1MY/Ib -Oprindelig meddelelse- Fra: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] På vegne af Ken Swaggart Sendt: 04 March 2013 17:03 Til: i8cvs; Amsat - BBs Emne: [amsat-bb] Re: STRaND1 polarity shift observation Domenico, Thanks for sending the K4KJ article. However my question was why does STRaND1, which only has a whip antenna, sometimes appear to exhibit circular polarity characteristics? I would expect a whip antenna transmitting from space to have the same signal strength on the ground using either RH or LH polarity on my receiving antenna. 73, Ken, W7KKE -Original Message- From: i8cvs Sent: Monday, March 04, 2013 00:42 To: Ken Swaggart ; Amsat - BBs Subject: Re: [amsat-bb] STRaND1 polarity shift observation Hi Ken, W7KKE The answere to your question is clearly described into the zipped article "Circular Polarization" by K4KJ, 5 MB long that I have sent to you in a separate email. 73" de i8CVS Domenico - Original Message - From: "Ken Swaggart" To: Sent: Monday, March 04, 2013 5:10 AM Subject: [amsat-bb] STRaND1 polarity shift observation > During my last pass at 0332Z, max elevation 45 degrees out over the Pacific, > I noticed that STRaND1 was stronger when I selected LHCP while approaching > TCA. After TCA, RHCP was stronger while it was receding. I believe this > cubesat uses a whip, so not sure what is causing this. > > Anyone have an idea why? > > Tnx, > Ken, W7KKE > CN75xa > > > ___ > 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 ___ 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: STRaND1 polarity shift observation
Ken, To add to what others have said, real CP antennas are not really circular. They are elliptical, due to slight differences in the lengths of the phasing harnesses, lack of isolation between the two sets of elements, etc. That means, even for a perfect linear antenna, directly on the axis, that if you rotate it there will be preferred directions. As you get further from the axis, the ellipticity becomes more pronounced. Throw in the fact that the spacecraft antennas may not, due to interactions, be perfectly linear, and it is not unexpected to see what you are reporting. A helix antenna, while not switchable, will be more nearly CP but will normally have a slight variation. 73s, Alan WA4SCA ___ 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: STRaND1 polarity shift observation
Hi Ken,W7KKE If STRaND1 has a circularly polarized crossed dipole antenna like that depicted in Fig 12 of the article "The Advantages of Circular Polarization for Amateur Satellite Ground Station " by K4KJ already in your hands than it is easy to understand why STRaND1 was stronger when you selected LHCP while approaching TCA and why after TCA, RHCP was stronger while the satellite was receding. Fig-12 shows that if two crossed dipoles are mounted over the same plane and are supplied with 90 degrees out of phase than the polarizazion is RHCP in one axial direction and LHCP in the opposite axial direction and this can explain why the signal was stronger when you selected LHCP while approaching TCA and why after TCA, RHCP was stronger while the satellite was receding. BTW unfortunately actually there are not official informations from AMSAT-UK about the polarization of the STRaND1 70 cm antenna and without this information it's very difficult to answere your question. 73" de i8CVS Domenico - Original Message - From: "Ken Swaggart" To: "i8cvs" ; "Amsat - BBs" Sent: Monday, March 04, 2013 5:02 PM Subject: Re: [amsat-bb] STRaND1 polarity shift observation > Domenico, > > Thanks for sending the K4KJ article. > > However my question was why does STRaND1, which only has a whip antenna, > sometimes appear to exhibit circular polarity characteristics? I would > expect a whip antenna transmitting from space to have the same signal > strength on the ground using either RH or LH polarity on my receiving > antenna. > > 73, > Ken, W7KKE > > -Original Message- > From: i8cvs > Sent: Monday, March 04, 2013 00:42 > To: Ken Swaggart ; Amsat - BBs > Subject: Re: [amsat-bb] STRaND1 polarity shift observation > > Hi Ken, W7KKE > > The answere to your question is clearly described into the zipped article > "Circular Polarization" by K4KJ, 5 MB long that I have sent to you in > a separate email. > > 73" de > > i8CVS Domenico > > - Original Message - > From: "Ken Swaggart" > To: > Sent: Monday, March 04, 2013 5:10 AM > Subject: [amsat-bb] STRaND1 polarity shift observation > > > > During my last pass at 0332Z, max elevation 45 degrees out over the > Pacific, > > I noticed that STRaND1 was stronger when I selected LHCP while approaching > > TCA. After TCA, RHCP was stronger while it was receding. I believe this > > cubesat uses a whip, so not sure what is causing this. > > > > Anyone have an idea why? > > > > Tnx, > > Ken, W7KKE > > CN75xa > > > > > > ___ > > 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: STRaND1 polarity shift observation
Hi Dom, Well this is not "official" but I can advise that the antennas on Strand-1 are both single 1/4 wave monopoles. They project from near the corners of the structure as indicated here http://www.google.co.uk/imgres?q=strand-1&hl=en&biw=804&bih=559&tbm=isch&tbnid=54d2HB8b425s7M:&imgrefurl=http://eandt.theiet.org/magazine/2012/03/satellite-expertise-above.cfm&docid=p-bcchRIAKhudM&imgurl=http://eandt.theiet.org/magazine/2012/03/images/640_strand-1.jpg&w=640&h=426&ei=6rI1UezVLoW0PNzugIgB&zoom=1&ved=1t:3588,r:0,s:0,i:80&iact=rc&dur=3695&sig=109122702080401960358&page=1&tbnh=166&tbnw=243&start=0&ndsp=10&tx=134&ty=96 sorry for the long link! I do not know whether the satellite attitude has yet been stabilised nor whether the solar panels have been deployed but there is not much sign of rapid signal strength changes during a pass. cheers Graham -Original Message----- From: i8cvs Sent: Tuesday, March 05, 2013 12:02 AM To: Ken Swaggart ; Amsat - BBs Subject: [amsat-bb] Re: STRaND1 polarity shift observation Hi Ken,W7KKE If STRaND1 has a circularly polarized crossed dipole antenna like that depicted in Fig 12 of the article "The Advantages of Circular Polarization for Amateur Satellite Ground Station " by K4KJ already in your hands than it is easy to understand why STRaND1 was stronger when you selected LHCP while approaching TCA and why after TCA, RHCP was stronger while the satellite was receding. Fig-12 shows that if two crossed dipoles are mounted over the same plane and are supplied with 90 degrees out of phase than the polarizazion is RHCP in one axial direction and LHCP in the opposite axial direction and this can explain why the signal was stronger when you selected LHCP while approaching TCA and why after TCA, RHCP was stronger while the satellite was receding. BTW unfortunately actually there are not official informations from AMSAT-UK about the polarization of the STRaND1 70 cm antenna and without this information it's very difficult to answere your question. 73" de i8CVS Domenico - Original Message - From: "Ken Swaggart" To: "i8cvs" ; "Amsat - BBs" Sent: Monday, March 04, 2013 5:02 PM Subject: Re: [amsat-bb] STRaND1 polarity shift observation Domenico, Thanks for sending the K4KJ article. However my question was why does STRaND1, which only has a whip antenna, sometimes appear to exhibit circular polarity characteristics? I would expect a whip antenna transmitting from space to have the same signal strength on the ground using either RH or LH polarity on my receiving antenna. 73, Ken, W7KKE -Original Message- From: i8cvs Sent: Monday, March 04, 2013 00:42 To: Ken Swaggart ; Amsat - BBs Subject: Re: [amsat-bb] STRaND1 polarity shift observation Hi Ken, W7KKE The answere to your question is clearly described into the zipped article "Circular Polarization" by K4KJ, 5 MB long that I have sent to you in a separate email. 73" de i8CVS Domenico - Original Message - From: "Ken Swaggart" To: Sent: Monday, March 04, 2013 5:10 AM Subject: [amsat-bb] STRaND1 polarity shift observation > During my last pass at 0332Z, max elevation 45 degrees out over the Pacific, > I noticed that STRaND1 was stronger when I selected LHCP while approaching > TCA. After TCA, RHCP was stronger while it was receding. I believe this > cubesat uses a whip, so not sure what is causing this. > > Anyone have an idea why? > > Tnx, > Ken, W7KKE > CN75xa > > > ___ > 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 ___ 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: STRaND1 polarity shift observation
I can confirm the comments below. I use a RHCP QFHA and some times I abruptly lost the satellite, most of the time the fade-out of the signal is pronounced when the sat pass the TCA and then... you lost it... This weekend I going to build the LHCP version... El 04/03/13 11:51, Ib Christoffersen escribió: Hi Ken, You can experience the same effect from SO-50 when using circularly polarized antennas on ground. SO-50 also have linear antennas for the FM repeater. I must change between RHCP and LHCP to get maximum signal during a pass. Sometimes the difference is from zero to a very good signal. ___ 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
