M2 LEO pack - which polarization to use
In the past I saw a lot of discussion on if it was better to use RHCP or LHCP, but today most of the LEO satellites use linear polarization.
I may be mistaken but the only LEO satellite that I know of that uses circular polarization is SO50, which uses LHCP for the 70 cm downlink.
I am in the process of replacing a dual band linear antenna with the M2 LEO pack. I was thinking about setting the 70 cm antenna for LHCP and the 2M antenna for RHCP. This would maximize the downlink from SO50 but also give me a lot of attenuation between 2M and 70 CM which would help with desense.
I have a desense problem with my current Cushcraft antenna, even with a diplexer as a desense filter. For the LEO pack antennas I will not be using M2's aluminum boom, but instead have a 12 ft fiberglass boom.
Am I missing something or is this the "best" way to go? Most of my operation is thru the linear SSB band birds.
73,
Don K9AQ
Hi Don,
Your rational seems reasonable to me. And you can always change the 70cm to RHCP if needed....tho the first time, while on the ground, is easiest ;)
I learned the power of polarity with AO-51. Built an 8 turn G3RUH helix RHCP for 70 cm and wondered why it was so hard to hear the one transmitter. I put up an M2 with LHCP and WOW what a difference. Was fun being able to listen to both at the same time!
73, Mark N8MH
On Wed, Apr 7, 2021 at 6:47 PM Don Solberg dsolberg8132@gmail.com wrote:
In the past I saw a lot of discussion on if it was better to use RHCP or LHCP, but today most of the LEO satellites use linear polarization.
I may be mistaken but the only LEO satellite that I know of that uses circular polarization is SO50, which uses LHCP for the 70 cm downlink.
I am in the process of replacing a dual band linear antenna with the M2 LEO pack. I was thinking about setting the 70 cm antenna for LHCP and the 2M antenna for RHCP. This would maximize the downlink from SO50 but also give me a lot of attenuation between 2M and 70 CM which would help with desense.
I have a desense problem with my current Cushcraft antenna, even with a diplexer as a desense filter. For the LEO pack antennas I will not be using M2's aluminum boom, but instead have a 12 ft fiberglass boom.
Am I missing something or is this the "best" way to go? Most of my operation is thru the linear SSB band birds.
73,
Don K9AQ
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SO-50 is linearly polarized as far as I know. It has a 1/4 wave whip for transmitting. Circular polarization will help you avoid the need to match polarizations as it tumbles.
Lilacsat-2 has a circularly polarized downlink, but because the satellite tumbles, at any given point you might be receiving LHCP, RHCP, or linear polarization depending on its orientation. You can imagine it as a helical antenna tumbling around. So at some points you'll get fades unless you can flip your CP.
You're only stuck needing a specific polarization for satellites that are stabilized, for example if you want to receive NOAA APT.
-Stephen DeVience N8URE
participants (3)
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Don Solberg -
Mark L. Hammond -
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