About 10 years ago got interested in sat radio and bought a Left Circular Quadrifilar Helix Antenna which got good review in QST. Didnt use it and now retired and trying to get on sat. Evidently most ham sats are right circular and depending on what I read. there is a 30db OR 3db loss going from one circular polarization to another. Which is it?
Thanks Roger N3RC
Hi Roger,
Going from left to right, or right to left, with both sides being circular is in that 30db loss realm. I recall it being more like 20db, but once you get in that range, a few db either way kind of doesn't matter. In practice it's not quite that bad, since in practice nothing is perfectly circular, but, yeah, not a recipe for success.
Crossing circular (either handed) with linear is 3db, I believe. Or was it 6? Anyway, not impossibly bad. Hopefully you also have a preamp at the antenna, which will offset a lot of this. If not, I'd invest in one, regardless of the polarization topic.
I have a pair of switchable beam antennas for satellite work. My observation is that most of the newer satellites these days appear to be linear, and I've noticed that while there appears to be some difference between right vs left on the ground, crossed with their linear signals, most of the time it's not fatal. Either can work for at least part of the pass.
Bottom line is that you've got a workable antenna. Try it and see what you get.
Greg KO6TH
Roger Cooper wrote:
About 10 years ago got interested in sat radio and bought a Left Circular Quadrifilar Helix Antenna which got good review in QST. Didnt use it and now retired and trying to get on sat. Evidently most ham sats are right circular and depending on what I read. there is a 30db OR 3db loss going from one circular polarization to another. Which is it?
Thanks Roger N3RC _______________________________________________ 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
Roger / Greg,
Greg is correct the CubeSats appear to be mostly linear polarized. Using a RHCP or LHCP polarized ground antenna will limit your "satellite tumble" loss to 3db. I also have x-pol yagis and using CP on CubeSats makes operation a little easier but you give up a minimum of 3db on RX and TX However, satellite operation is not really weak signal and there is usually plenty of link margin. I agree, using 2m and 70cm preamps will greatly enhance your satellite experience.
I have used both switchable linear x-pol yagis and RHCP yagis on CubeSats and FO-29 / AO-7. They both work - RHCP (circular) will minimize the deep signal nulls as the satellite tumbles. Be careful, I think FO-29 is a CP satellite so you need to pick the correct uplink sense. Linear will be ok FO29.
This is the beauty of the handheld Arrow yagi. The human brain / ear combination directs this low gain linear polarized yagi to exactly the correct polarization everytime without the 3db CP penalty. The only problem with the Arrow is that you need to be outside in the rain and snow for every satellite pass. :) BTW - I have seen Arrow yagis mounted on Az/El rotors but now you lose the polarization correction.
It's ham radio - try everything!
73 - Paul - W2HRO
On Fri, Oct 7, 2016 at 2:00 PM, Greg D ko6th.greg@gmail.com wrote:
Hi Roger,
Going from left to right, or right to left, with both sides being circular is in that 30db loss realm. I recall it being more like 20db, but once you get in that range, a few db either way kind of doesn't matter. In practice it's not quite that bad, since in practice nothing is perfectly circular, but, yeah, not a recipe for success.
Crossing circular (either handed) with linear is 3db, I believe. Or was it 6? Anyway, not impossibly bad. Hopefully you also have a preamp at the antenna, which will offset a lot of this. If not, I'd invest in one, regardless of the polarization topic.
I have a pair of switchable beam antennas for satellite work. My observation is that most of the newer satellites these days appear to be linear, and I've noticed that while there appears to be some difference between right vs left on the ground, crossed with their linear signals, most of the time it's not fatal. Either can work for at least part of the pass.
Bottom line is that you've got a workable antenna. Try it and see what you get.
Greg KO6TH
Roger Cooper wrote:
About 10 years ago got interested in sat radio and bought a Left Circular Quadrifilar Helix Antenna which got good review in QST. Didnt use it and now retired and trying to get on sat. Evidently most ham sats are right circular and depending on what I read. there is a 30db OR 3db loss going from one circular polarization to another. Which is it?
Thanks Roger N3RC _______________________________________________ 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
Theoretically, going from right hand to left hand circular polarization results in an infinite loss. However, in practice, the loss is generally around 20 dB although, in certain circumstances, it can be as high as 30 dB, or more.
It is the same going between vertical polarization and horizontal polarization. Theoretically infinite but in practice more like 20 dB.
Going from linear polarization to either left hand or right hand circular polarization results in a 3 dB loss. Glen, K9STH Website: http://k9sth.net
From: Greg D ko6th.greg@gmail.com To: Roger Cooper rogern3rc@gmail.com Cc: amsat-bb@amsat.org Sent: Friday, October 7, 2016 1:00 PM Subject: Re: [amsat-bb] Loss Between Right and Left Circular
Hi Roger,
Going from left to right, or right to left, with both sides being circular is in that 30db loss realm. I recall it being more like 20db, but once you get in that range, a few db either way kind of doesn't matter. In practice it's not quite that bad, since in practice nothing is perfectly circular, but, yeah, not a recipe for success.
Crossing circular (either handed) with linear is 3db, I believe. Or was it 6? Anyway, not impossibly bad. Hopefully you also have a preamp at the antenna, which will offset a lot of this. If not, I'd invest in one, regardless of the polarization topic.
I have a pair of switchable beam antennas for satellite work. My observation is that most of the newer satellites these days appear to be linear, and I've noticed that while there appears to be some difference between right vs left on the ground, crossed with their linear signals, most of the time it's not fatal. Either can work for at least part of the pass.
Bottom line is that you've got a workable antenna. Try it and see what you get.
participants (4)
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Glen Zook -
Greg D -
Paul Andrews -
Roger Cooper