"The antennas I see in the photos of satellites we work are whips. Is the polarization becoming "circularized" as it re-enters earth's atmosphere or something?"

Yep, that is exactly what is happening. It is called Faraday Rotation, and as the signal from the satellite passes through the ionosphere, all sorts of polarity changes can and do happen. A linear polarized satellite antenna (horizontal or vertical) can appear to be the opposite or somewhere in between. That's why folks rotate their Arrow or Elk antennas -- trying to match the polarity.

Using a circular polarized antenna helps a bunch -- it doesn't matter what the polarity of the linear satellite antenna happens to be at any moment in time.

But there is no free lunch -- Even a circular polarized antenna might need to be switched from Right Hand Circular Polarization (the default) to LHCP from time to time depending on what nasty thing the ionosphere is doing at any given moment. Changing the polarity switch might bring a S0 signal up to S5, a 30 dB improvement. I had that happen to me during a recent ARISS contact.

73, Bob, WB4SON

On Mon, May 30, 2016 at 8:25 PM, Doug Andrews [email protected] wrote:

I too have wondered about this. I have not had much trouble hitting SO-50 and some success on AO-85 with a 5 watt handheld and arrow antenna without turning it. Worth a try. DougKG7UNU

Sent from my Sprint Samsung Galaxy® Note 4.

-------- Original message -------- From: Ken Alexander [email protected] Date: 5/30/16 4:41 PM (GMT-08:00) To: [email protected] Subject: [amsat-bb] Polarization

I clipped this from another message because I didn't want to drag the discussion off course. It's a question I've been wondering about since getting into this a few short weeks ago.

I've also read (but haven't tried yet) about the trick of rotating the antenna 90 degrees on transmit, once you've established the best receive orientation.

73 de Bill, KG5FQX

So far, with SO-20 I have rotated my Arrow antenna for best reception of the downlink and don't think I've had too much trouble being heard. At the same time I have wondered whether I should twist the antenna when transmitting to orient the 2m elements to give the same polarization as in receive. I don't know if this is a good idea or not, and frankly I have enough trouble remembering calls and grids, tracking the satellite, adjusting frequency and switching back to the correct VFO to worry about one more thing.

I've seen that some commercial OSCAR antennas use circular polarization. The antennas I see in the photos of satellites we work are whips. Is the polarization becoming "circularized" as it re-enters earth's atmosphere or something?

Comments and observations would be most welcome!

73,

Ken Alexander VE3HLS, FN03

---

Sent via [email protected]. 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 [email protected]. 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

PCSAT spins at about 0.6 RPM and PSAT spins between 3 and 6 PM and you can decode the telemetry easily with a pen and paper to see what it is currently doing. http://aprs.org/psat.html

Even if a satellite did not spin at all, it would still rotate relative to you almost 180 degrees from horizon to horizon. Bob, WB4aPR

-----Original Message----- From: AMSAT-BB [mailto:[email protected]] On Behalf Of Ken Alexander Sent: Thursday, June 02, 2016 7:29 PM To: Bob Cc: AMSAT-BB Subject: [amsat-bb] Does SO-50 Tumble? Was: "Polarization"

So far, I am only active on SO-50 and I have to say I’m impressed with the reception quality with my TH-D72A and Arrow antenna. The Arrow requires only a twist to peak the signal to very good levels. I’m starting to notice a pattern where certain polarization angles produce the best results at different times during a pass. It would be interesting if this turned out to be repeatable…and it leads to my next question: How much (if at all) does SO-50 or any other satellite tumble during its orbit? I am assuming that the current breed of ham satellites aren’t large enough to house motors or other devices to control their attitude, which makes me think they must tumble somewhat.

Once again, thank you all for your forbearance as I mine your collective knowledge to bring myself up to speed!

73,

Ken Alexander VE3HLS

On May 31, 2016, at 1:51 PM, Bob [email protected] wrote:

"The antennas I see in the photos of satellites we work are whips. Is the polarization becoming "circularized" as it re-enters earth's atmosphere or something?"

Yep, that is exactly what is happening. It is called Faraday Rotation, and as the signal from the satellite passes through the ionosphere, all sorts of polarity changes can and do happen. A linear polarized satellite antenna (horizontal or vertical) can appear to be the opposite or somewhere in between. That's why folks rotate their Arrow or Elk antennas -- trying to match the polarity.

Using a circular polarized antenna helps a bunch -- it doesn't matter what the polarity of the linear satellite antenna happens to be at any moment in time.

But there is no free lunch -- Even a circular polarized antenna might need to be switched from Right Hand Circular Polarization (the default) to LHCP from time to time depending on what nasty thing the ionosphere is doing at any given moment. Changing the polarity switch might bring a S0 signal up to S5, a 30 dB improvement. I had that happen to me during a recent ARISS contact.

73, Bob, WB4SON

On Mon, May 30, 2016 at 8:25 PM, Doug Andrews <[email protected] mailto:[email protected]> wrote:

I too have wondered about this. I have not had much trouble hitting SO-50 and some success on AO-85 with a 5 watt handheld and arrow antenna without turning it. Worth a try. DougKG7UNU

Sent from my Sprint Samsung Galaxy® Note 4.

-------- Original message -------- From: Ken Alexander <[email protected] mailto:[email protected]> Date: 5/30/16 4:41 PM (GMT-08:00) To: [email protected] mailto:[email protected] Subject: [amsat-bb] Polarization

I clipped this from another message because I didn't want to drag the discussion off course. It's a question I've been wondering about since getting into this a few short weeks ago.

I've also read (but haven't tried yet) about the trick of rotating the antenna 90 degrees on transmit, once you've established the best receive orientation.

73 de Bill, KG5FQX

So far, with SO-20 I have rotated my Arrow antenna for best reception of the downlink and don't think I've had too much trouble being heard. At the same time I have wondered whether I should twist the antenna when transmitting to orient the 2m elements to give the same polarization as in receive. I don't know if this is a good idea or not, and frankly I have enough trouble remembering calls and grids, tracking the satellite, adjusting frequency and switching back to the correct VFO to worry about one more thing.

I've seen that some commercial OSCAR antennas use circular polarization. The antennas I see in the photos of satellites we work are whips. Is the polarization becoming "circularized" as it re-enters earth's atmosphere or something?

Comments and observations would be most welcome!

73,

Ken Alexander VE3HLS, FN03

---

Sent via [email protected] mailto:[email protected]. 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 _______________________________________________ Sent via [email protected] mailto:[email protected]. 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

_______________________________________________ Sent via [email protected]. 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

Most us passive magnetic stabilization and some sort of solar pressure induced spin. They "tumble" crossing the magnetic equator, and wobble elsewhere.

73, Drew KO4MA

On Jun 2, 2016, at 7:28 PM, Ken Alexander [email protected] wrote:

So far, I am only active on SO-50 and I have to say I’m impressed with the reception quality with my TH-D72A and Arrow antenna. The Arrow requires only a twist to peak the signal to very good levels. I’m starting to notice a pattern where certain polarization angles produce the best results at different times during a pass. It would be interesting if this turned out to be repeatable…and it leads to my next question: How much (if at all) does SO-50 or any other satellite tumble during its orbit? I am assuming that the current breed of ham satellites aren’t large enough to house motors or other devices to control their attitude, which makes me think they must tumble somewhat.

Once again, thank you all for your forbearance as I mine your collective knowledge to bring myself up to speed!

73,

Ken Alexander VE3HLS

...

On May 31, 2016, at 1:51 PM, Bob [email protected] wrote:

"The antennas I see in the photos of satellites we work are whips. Is the polarization becoming "circularized" as it re-enters earth's atmosphere or something?"

Yep, that is exactly what is happening. It is called Faraday Rotation, and as the signal from the satellite passes through the ionosphere, all sorts of polarity changes can and do happen. A linear polarized satellite antenna (horizontal or vertical) can appear to be the opposite or somewhere in between. That's why folks rotate their Arrow or Elk antennas -- trying to match the polarity.

Using a circular polarized antenna helps a bunch -- it doesn't matter what the polarity of the linear satellite antenna happens to be at any moment in time.

But there is no free lunch -- Even a circular polarized antenna might need to be switched from Right Hand Circular Polarization (the default) to LHCP from time to time depending on what nasty thing the ionosphere is doing at any given moment. Changing the polarity switch might bring a S0 signal up to S5, a 30 dB improvement. I had that happen to me during a recent ARISS contact.

73, Bob, WB4SON

On Mon, May 30, 2016 at 8:25 PM, Doug Andrews <[email protected] mailto:[email protected]> wrote:

I too have wondered about this. I have not had much trouble hitting SO-50 and some success on AO-85 with a 5 watt handhel