I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the rotator without harm since it has the solid reflector behind the helix?
Bob W7OTJ (was WL7CQX)
That's pretty much what I did, though with different antennas. Also put the AO-40 dish on the other side of the rotor from the 23cm helix, so it went 70cm, 2.4gig, rotor, 23cm, 2m. Put things as far away from each other as you can, without running out of crossboom.
I was very concerned about having the 70cm beam (uplink) so close - inches - to the 2.4 ghz dish (downlink), but it was fine. Good input filtering in the 2.4 ghz Khune preamp, I guess. More recently, Mode L/v on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a lot less power on 23cm than I did with AO-40 on 70cm.
Greg KO6TH
Bob Hammond wrote:
I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the rotator without harm since it has the solid reflector behind the helix?
Bob W7OTJ (was WL7CQX) _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Greg,
what are you using for your 13 cm dish?
-Eric KI7LTT
On Mon, Nov 26, 2018 at 10:11 AM Greg D ko6th.greg@gmail.com wrote:
That's pretty much what I did, though with different antennas. Also put the AO-40 dish on the other side of the rotor from the 23cm helix, so it went 70cm, 2.4gig, rotor, 23cm, 2m. Put things as far away from each other as you can, without running out of crossboom.
I was very concerned about having the 70cm beam (uplink) so close - inches - to the 2.4 ghz dish (downlink), but it was fine. Good input filtering in the 2.4 ghz Khune preamp, I guess. More recently, Mode L/v on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a lot less power on 23cm than I did with AO-40 on 70cm.
Greg KO6TH
Bob Hammond wrote:
I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the rotator without harm since it has the solid reflector behind the helix?
Bob W7OTJ (was WL7CQX) _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Greg,
Do you use polarity switches on your yagis? If you do, is it worth the effort?
73s,
Bob W7OTJ
On Mon, Nov 26, 2018 at 10:08 AM Greg D ko6th.greg@gmail.com wrote:
That's pretty much what I did, though with different antennas. Also put the AO-40 dish on the other side of the rotor from the 23cm helix, so it went 70cm, 2.4gig, rotor, 23cm, 2m. Put things as far away from each other as you can, without running out of crossboom.
I was very concerned about having the 70cm beam (uplink) so close - inches - to the 2.4 ghz dish (downlink), but it was fine. Good input filtering in the 2.4 ghz Khune preamp, I guess. More recently, Mode L/v on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a lot less power on 23cm than I did with AO-40 on 70cm.
Greg KO6TH
Bob Hammond wrote:
I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the rotator without harm since it has the solid reflector behind the helix?
Bob W7OTJ (was WL7CQX) _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
On Fri, Dec 14, 2018 at 10:58 AM Bob Hammond propgrinder@gmail.com wrote:
Do you use polarity switches on your yagis? If you do, is it worth
the effort?
No and no.
I had polarity switching on long yagis back in AO-10 & AO-13 days and it was helpful. But for the LEO satellites we have now, it's rare to have a fade so deep that one can't copy. -- Mark D. Johns KØJM / MØGZO / ex-9H3DJ / ex-KØMDJ Brooklyn Park, MN USA EN35hd ----------------------------------------------- "Heaven goes by favor; if it went by merit, you would stay out and your dog would go in." ---Mark Twain
Greg,
73s,
Bob W7OTJ
On Mon, Nov 26, 2018 at 10:08 AM Greg D ko6th.greg@gmail.com wrote:
That's pretty much what I did, though with different antennas. Also put the AO-40 dish on the other side of the rotor from the 23cm helix, so it went 70cm, 2.4gig, rotor, 23cm, 2m. Put things as far away from each other as you can, without running out of crossboom.
I was very concerned about having the 70cm beam (uplink) so close - inches - to the 2.4 ghz dish (downlink), but it was fine. Good input filtering in the 2.4 ghz Khune preamp, I guess. More recently, Mode L/v on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a lot less power on 23cm than I did with AO-40 on 70cm.
Greg KO6TH
Bob Hammond wrote:
I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the
rotator
without harm since it has the solid reflector behind the helix?
Bob W7OTJ (was WL7CQX) _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views
of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Bob,
So that all may fully understand:
Most LEO’s use monopoles or dipoles (on VHF/UHF) which are actually linear and not circular polarization, but the birds are spinning and tumbling therefore the polarization can be H, V or any angle. If you use H or V pole at the ground station the fading may be as high at 30dB therefore it is recommended to use circular polarization at the ground station as maximum fade would be around 3 dB whatever the satellite polarization may be.
I suggest that you use RHCP without polarisation switch, except if you wish to spend some money to experiment with same. I have the possibility to switch polarization but it is not used at all.
Hope this help.
73
Jean Marc (3B8DU)
On Dec 15, 2018, at 1:40 AM, Mark D. Johns mjohns+K0JM@luther.edu wrote:
On Fri, Dec 14, 2018 at 10:58 AM Bob Hammond propgrinder@gmail.com wrote:
Do you use polarity switches on your yagis? If you do, is it worth
the effort?
No and no.
I had polarity switching on long yagis back in AO-10 & AO-13 days and it was helpful. But for the LEO satellites we have now, it's rare to have a fade so deep that one can't copy. -- Mark D. Johns KØJM / MØGZO / ex-9H3DJ / ex-KØMDJ Brooklyn Park, MN USA EN35hd
"Heaven goes by favor; if it went by merit, you would stay out and your dog would go in." ---Mark Twain
Greg,
73s,
Bob W7OTJ
On Mon, Nov 26, 2018 at 10:08 AM Greg D ko6th.greg@gmail.com wrote:
That's pretty much what I did, though with different antennas. Also put the AO-40 dish on the other side of the rotor from the 23cm helix, so it went 70cm, 2.4gig, rotor, 23cm, 2m. Put things as far away from each other as you can, without running out of crossboom.
I was very concerned about having the 70cm beam (uplink) so close - inches - to the 2.4 ghz dish (downlink), but it was fine. Good input filtering in the 2.4 ghz Khune preamp, I guess. More recently, Mode L/v on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a lot less power on 23cm than I did with AO-40 on 70cm.
Greg KO6TH
Bob Hammond wrote:
I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the
rotator
without harm since it has the solid reflector behind the helix?
Bob W7OTJ (was WL7CQX) _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views
of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Thanks Jean Marc. That is exactly the answer I was seeking. I have 2m and 70cm CP yagis with RHCP.
Bob W7OTJ
On Sat, Dec 15, 2018 at 7:44 AM Jean Marc Momple jean.marc.momple@gmail.com wrote:
Bob,
So that all may fully understand:
Most LEO’s use monopoles or dipoles (on VHF/UHF) which are actually linear and not circular polarization, but the birds are spinning and tumbling therefore the polarization can be H, V or any angle. If you use H or V pole at the ground station the fading may be as high at 30dB therefore it is recommended to use circular polarization at the ground station as maximum fade would be around 3 dB whatever the satellite polarization may be.
I suggest that you use RHCP without polarisation switch, except if you wish to spend some money to experiment with same. I have the possibility to switch polarization but it is not used at all.
Hope this help.
73
Jean Marc (3B8DU)
On Dec 15, 2018, at 1:40 AM, Mark D. Johns mjohns+K0JM@luther.edu
wrote:
On Fri, Dec 14, 2018 at 10:58 AM Bob Hammond propgrinder@gmail.com wrote:
Do you use polarity switches on your yagis? If you do, is it worth
the effort?
No and no.
I had polarity switching on long yagis back in AO-10 & AO-13 days and it was helpful. But for the LEO satellites we have now, it's rare to have a fade so deep that one can't copy. -- Mark D. Johns KØJM / MØGZO / ex-9H3DJ / ex-KØMDJ Brooklyn Park, MN USA EN35hd
"Heaven goes by favor; if it went by merit, you would stay out and your dog would go in." ---Mark Twain
Greg,
73s,
Bob W7OTJ
On Mon, Nov 26, 2018 at 10:08 AM Greg D ko6th.greg@gmail.com wrote:
That's pretty much what I did, though with different antennas. Also
put
the AO-40 dish on the other side of the rotor from the 23cm helix, so
it
went 70cm, 2.4gig, rotor, 23cm, 2m. Put things as far away from each other as you can, without running out of crossboom.
I was very concerned about having the 70cm beam (uplink) so close - inches - to the 2.4 ghz dish (downlink), but it was fine. Good input filtering in the 2.4 ghz Khune preamp, I guess. More recently, Mode
L/v
on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a lot less power on 23cm than I did with AO-40 on 70cm.
Greg KO6TH
Bob Hammond wrote:
I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the
rotator
without harm since it has the solid reflector behind the helix?
Bob W7OTJ (was WL7CQX) _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views
of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions
expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
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Bob,
Sure it will work fine for nearly all birds.
73
Jean Marc (3B8DU)
On Dec 15, 2018, at 8:08 PM, Bob Hammond propgrinder@gmail.com wrote:
Thanks Jean Marc. That is exactly the answer I was seeking. I have 2m and 70cm CP yagis with RHCP.
Bob W7OTJ
On Sat, Dec 15, 2018 at 7:44 AM Jean Marc Momple <jean.marc.momple@gmail.com mailto:jean.marc.momple@gmail.com> wrote: Bob,
So that all may fully understand:
Most LEO’s use monopoles or dipoles (on VHF/UHF) which are actually linear and not circular polarization, but the birds are spinning and tumbling therefore the polarization can be H, V or any angle. If you use H or V pole at the ground station the fading may be as high at 30dB therefore it is recommended to use circular polarization at the ground station as maximum fade would be around 3 dB whatever the satellite polarization may be.
I suggest that you use RHCP without polarisation switch, except if you wish to spend some money to experiment with same. I have the possibility to switch polarization but it is not used at all.
Hope this help.
73
Jean Marc (3B8DU)
On Dec 15, 2018, at 1:40 AM, Mark D. Johns <mjohns+K0JM@luther.edu mailto:mjohns%2BK0JM@luther.edu> wrote:
On Fri, Dec 14, 2018 at 10:58 AM Bob Hammond <propgrinder@gmail.com mailto:propgrinder@gmail.com> wrote:
Do you use polarity switches on your yagis? If you do, is it worth
the effort?
No and no.
I had polarity switching on long yagis back in AO-10 & AO-13 days and it was helpful. But for the LEO satellites we have now, it's rare to have a fade so deep that one can't copy. -- Mark D. Johns KØJM / MØGZO / ex-9H3DJ / ex-KØMDJ Brooklyn Park, MN USA EN35hd
"Heaven goes by favor; if it went by merit, you would stay out and your dog would go in." ---Mark Twain
Greg,
73s,
Bob W7OTJ
On Mon, Nov 26, 2018 at 10:08 AM Greg D <ko6th.greg@gmail.com mailto:ko6th.greg@gmail.com> wrote:
That's pretty much what I did, though with different antennas. Also put the AO-40 dish on the other side of the rotor from the 23cm helix, so it went 70cm, 2.4gig, rotor, 23cm, 2m. Put things as far away from each other as you can, without running out of crossboom.
I was very concerned about having the 70cm beam (uplink) so close - inches - to the 2.4 ghz dish (downlink), but it was fine. Good input filtering in the 2.4 ghz Khune preamp, I guess. More recently, Mode L/v on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a lot less power on 23cm than I did with AO-40 on 70cm.
Greg KO6TH
Bob Hammond wrote:
I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the
rotator
without harm since it has the solid reflector behind the helix?
Bob W7OTJ (was WL7CQX) _______________________________________________ Sent via AMSAT-BB@amsat.org mailto:AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views
of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb http://www.amsat.org/mailman/listinfo/amsat-bb
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I would add to this that there is one workhorse satellite on orbit that is circular and changes with location. In the northern hemisphere FO-29 is RHCP when to the south of the station and LHCP when to the north. It makes a very large difference.
In addition, while cubesats of the 1U to 3U size typically use a whip (linear) because there isn't real estate for anything circular, for 6U and larger a canted turnstile is a better choice and is circular. In that case they are typically wired for RHCP when the antenna ends faces earth but if it tumbles or flips the sense will change. When facing away it will be LHCP to the ground station.
This question has been rattling around for at least since the 1990 AMSAT-NA microsats (which were canted turnstiles on the UHF downlink). For those satellites the downlink was RCHP in the northern hemisphere and LCHP in the southern, except for LO-19 which was reversed. I wrote a paper on this for the 1991 AMSAT Space Sympoisum (or it might have been 1992). So I tend to suggest that folks just getting started with a hand held antenna a linear antenna is fine because they are a bit lighter and less cumbersome to handle, and less expensive. But if you are building a fixed "base" station I still suggest including sense switching. It will make a large difference with FO29 and you will be ready for the next one that uses circular. Given there are probably 100 in various stages of design and construction and rides are plentiful it seems worth the investment.
Jim
Jim White, WD0E jim@coloradosatellite.com On 12/15/2018 8:44 AM, Jean Marc Momple wrote:
Bob,
So that all may fully understand:
Most LEO’s use monopoles or dipoles (on VHF/UHF) which are actually linear and not circular polarization, but the birds are spinning and tumbling therefore the polarization can be H, V or any angle. If you use H or V pole at the ground station the fading may be as high at 30dB therefore it is recommended to use circular polarization at the ground station as maximum fade would be around 3 dB whatever the satellite polarization may be.
I suggest that you use RHCP without polarisation switch, except if you wish to spend some money to experiment with same. I have the possibility to switch polarization but it is not used at all.
Hope this help.
73
Jean Marc (3B8DU)
On Dec 15, 2018, at 1:40 AM, Mark D. Johns mjohns+K0JM@luther.edu wrote:
On Fri, Dec 14, 2018 at 10:58 AM Bob Hammond propgrinder@gmail.com wrote:
Do you use polarity switches on your yagis? If you do, is it worth
the effort?
No and no.
I had polarity switching on long yagis back in AO-10 & AO-13 days and it was helpful. But for the LEO satellites we have now, it's rare to have a fade so deep that one can't copy. -- Mark D. Johns KØJM / MØGZO / ex-9H3DJ / ex-KØMDJ Brooklyn Park, MN USA EN35hd
"Heaven goes by favor; if it went by merit, you would stay out and your dog would go in." ---Mark Twain
Greg,
73s,
Bob W7OTJ
On Mon, Nov 26, 2018 at 10:08 AM Greg D ko6th.greg@gmail.com wrote:
That's pretty much what I did, though with different antennas. Also put the AO-40 dish on the other side of the rotor from the 23cm helix, so it went 70cm, 2.4gig, rotor, 23cm, 2m. Put things as far away from each other as you can, without running out of crossboom.
I was very concerned about having the 70cm beam (uplink) so close - inches - to the 2.4 ghz dish (downlink), but it was fine. Good input filtering in the 2.4 ghz Khune preamp, I guess. More recently, Mode L/v on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a lot less power on 23cm than I did with AO-40 on 70cm.
Greg KO6TH
Bob Hammond wrote:
I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the
rotator
without harm since it has the solid reflector behind the helix?
Bob W7OTJ (was WL7CQX) _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views
of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Jim,
I tend to disagree about having polarization switch at the base station (costing several hundreds $, just a questions on own means) for improving signal (already good and only 3 dB loss/fading), except from only few birds.
I take the example you stated, FO-29 is so strong that even with a magnetic 1/4 wave whip of the roof of my car I made QSO’s 59+ both ways. You rightly advised that one may start with handhelds, this works for many sats including FO-29 and fully agree.
I would really appreciate that you send me your paper on this subject and I will surely have some learning there, this is the beauty of the hobby sharing experiment and experience make one and all better eventually.
Have a nice end of WE.
Jean Marc (3B8DU)
On Dec 15, 2018, at 8:09 PM, Jim White jim@coloradosatellite.com wrote:
I would add to this that there is one workhorse satellite on orbit that is circular and changes with location. In the northern hemisphere FO-29 is RHCP when to the south of the station and LHCP when to the north. It makes a very large difference.
In addition, while cubesats of the 1U to 3U size typically use a whip (linear) because there isn't real estate for anything circular, for 6U and larger a canted turnstile is a better choice and is circular. In that case they are typically wired for RHCP when the antenna ends faces earth but if it tumbles or flips the sense will change. When facing away it will be LHCP to the ground station.
This question has been rattling around for at least since the 1990 AMSAT-NA microsats (which were canted turnstiles on the UHF downlink). For those satellites the downlink was RCHP in the northern hemisphere and LCHP in the southern, except for LO-19 which was reversed. I wrote a paper on this for the 1991 AMSAT Space Sympoisum (or it might have been 1992). So I tend to suggest that folks just getting started with a hand held antenna a linear antenna is fine because they are a bit lighter and less cumbersome to handle, and less expensive. But if you are building a fixed "base" station I still suggest including sense switching. It will make a large difference with FO29 and you will be ready for the next one that uses circular. Given there are probably 100 in various stages of design and construction and rides are plentiful it seems worth the investment.
Jim
Jim White, WD0E jim@coloradosatellite.com On 12/15/2018 8:44 AM, Jean Marc Momple wrote:
Bob,
So that all may fully understand:
Most LEO’s use monopoles or dipoles (on VHF/UHF) which are actually linear and not circular polarization, but the birds are spinning and tumbling therefore the polarization can be H, V or any angle. If you use H or V pole at the ground station the fading may be as high at 30dB therefore it is recommended to use circular polarization at the ground station as maximum fade would be around 3 dB whatever the satellite polarization may be.
I suggest that you use RHCP without polarisation switch, except if you wish to spend some money to experiment with same. I have the possibility to switch polarization but it is not used at all.
Hope this help.
73
Jean Marc (3B8DU)
On Dec 15, 2018, at 1:40 AM, Mark D. Johns mjohns+K0JM@luther.edu wrote:
On Fri, Dec 14, 2018 at 10:58 AM Bob Hammond propgrinder@gmail.com wrote:
Do you use polarity switches on your yagis? If you do, is it worth
the effort?
No and no.
I had polarity switching on long yagis back in AO-10 & AO-13 days and it was helpful. But for the LEO satellites we have now, it's rare to have a fade so deep that one can't copy. -- Mark D. Johns KØJM / MØGZO / ex-9H3DJ / ex-KØMDJ Brooklyn Park, MN USA EN35hd
"Heaven goes by favor; if it went by merit, you would stay out and your dog would go in." ---Mark Twain
Greg,
73s,
Bob W7OTJ
On Mon, Nov 26, 2018 at 10:08 AM Greg D ko6th.greg@gmail.com wrote:
That's pretty much what I did, though with different antennas. Also put the AO-40 dish on the other side of the rotor from the 23cm helix, so it went 70cm, 2.4gig, rotor, 23cm, 2m. Put things as far away from each other as you can, without running out of crossboom.
I was very concerned about having the 70cm beam (uplink) so close - inches - to the 2.4 ghz dish (downlink), but it was fine. Good input filtering in the 2.4 ghz Khune preamp, I guess. More recently, Mode L/v on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a lot less power on 23cm than I did with AO-40 on 70cm.
Greg KO6TH
Bob Hammond wrote:
I'm putting the following antennas on an 8-foot fiberglass crossboom:
M2 2MCP8A, 143-148 MHz C{ Gulf Alpha 70cm 8x8 CP WiMo Helix 23
I'm not sure how to calculate the proper spacing on the crossboom. I assume the 2m antenna should go on one end and the 70cm antenna on the opposite end. Can I mount the 23cm helical antenna very near the
rotator
without harm since it has the solid reflector behind the helix?
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Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
participants (6)
-
Bob Hammond -
Eric Garner -
Greg D -
Jean Marc Momple -
Jim White -
Mark D. Johns