Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
if the satellite is running RHCP and you have LHCP the VHF/UHF Manual handbook says 20 -30dB which is a lot! having spent ages getting a homebrew polarity control box to work just right, I can honestly say it was well worth the effort! regards Gus M0IKB ----- Original Message ----- From: "Tim Tapio" [email protected] To: [email protected] Sent: Friday, September 19, 2008 1:58 PM Subject: [amsat-bb] Polarity questions
Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
Sent via [email protected]. 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
....I agree with Gus. And the difference is 20-30 dB depending upon the construction, reflections, lobes of antennas and other complex parameters.
In general a Cross-Yagi which appears a very good circularity, then rising easily to 30 dB between RHCP-LHCP.
Tim, also keep in mind, by using CP the fading is much less and never the signal has too much "deep" . Having in mind that the LEOs changing quite often the polarization, I believe the switching between RHCP-LHCP is mandatory, if always you looking for good RX-TX conditions . A mere example was the last pass of AO-7 over my QTH . During the ascending orbit it was 5 S-units without preamp and almost close to TCA the signal dropped down to Zero (Q5). By changing my antenna to the opposite polarization, it was again 5 S-units. That is a great difference on receiving.
So, If you want just to play with LEOs and you are not looking for the optimum, you can do it by using stable polarization. However it's compromise and manytimes you will wonder why the satellite is too weak and some other times "booming".
73, Mak SV1BSX
----- Original Message ----- From: "Angus" [email protected] To: [email protected] Sent: Friday, September 19, 2008 5:29 PM Subject: [amsat-bb] Re: Polarity questions
if the satellite is running RHCP and you have LHCP the VHF/UHF Manual handbook says 20 -30dB which is a lot! having spent ages getting a homebrew polarity control box to work just right, I can honestly say it was well worth the effort! regards Gus M0IKB ----- Original Message ----- From: "Tim Tapio" [email protected] To: [email protected] Sent: Friday, September 19, 2008 1:58 PM Subject: [amsat-bb] Polarity questions
Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
Sent via [email protected]. 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 [email protected]. 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
Roughly 20-dB, assuming the signal is pure circular polarization. If it is linear, then -3 dB. 73, Ed
At 04:58 AM 9/19/2008, Tim Tapio wrote:
Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
Sent via [email protected]. 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
Tim, let me tell you my experience. I use the old Cushcraft AOP-1 antennas. 10x2 elements on 2 meters, and 8x2 on 440.
I have them in an X pattern, and I can hear and transmit to the birds pretty much throughout the entire pass.
These antennas are old, and were designed during the days of AO-10 & AO-13. But I have restored them, and they still work great for me today (except for DO-64). It amazes me that I can drop my output to 5 watts and still hear myself loud and clear on AO-7 as it gets close to LOS.
I would concentrate most of all on good quality coax. I use LMR400, about 80 feet of it, with a TS-2000. I don't use a preamp and my antennas are up about 25 feet and I have a blast!
73 de W4AS Sebastian
On Sep 19, 2008, at 8:58 AM, Tim Tapio wrote:
Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
Tim Tapio wrote:
Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
Sent via [email protected]. 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
The difference between RHCP and LHCP is 20 dB
The difference between Horizontal and Vertical Linear is 20 dB
The difference between (RHCP or LHCP) and (Horizontal or Vertical) is 3 dB
Ryan, NF0T
On Fri, September 19, 2008 16:58, Ryan Butler wrote:
Tim Tapio wrote:
Hi Tim,
How much signal reduction is there as the result of having the wrong circular polarization?
The difference between RHCP and LHCP is 20 dB
The difference between Horizontal and Vertical Linear is 20 dB
The difference between (RHCP or LHCP) and (Horizontal or Vertical) is 3 dB
If I understand right, you only get 3db extra when using CW/CCW but I have also read somewhere that you also lose 3db when running CW/CCW so why use Circulair polarisation and not just Horizontal or Vertical pol.
Ryan, NF0T
73's Jan / PE0SAT
By having circular polarisation that matches the satellite (RHCP or LHCP but the same polarity) you have very little QSB fading during the pass of the satellite. Using my own system I normally start a pass on Horizontal as the satellite is at AOS and then when it rises switch to the correct circular polarity and as the satellite gets near to LOS I am back on horizontal polarity with good quality signals through the entire pass. try listening to a NOAA weather satellite on 137mhz on a fixed polarity antenna i.e V or H and for some of the pass the signal is very good but as the signal changes polarity the signal drops down into the noise and through the satellite pass you will get these peaks and troughs of signals. This is why if possible it is best to use circular or better still have the ability to switch polarity during the pass. regards Gus ----- Original Message ----- From: "pe0sat" [email protected] To: [email protected] Sent: Friday, September 19, 2008 7:02 PM Subject: [amsat-bb] Re: Polarity questions
On Fri, September 19, 2008 16:58, Ryan Butler wrote:
Tim Tapio wrote:
Hi Tim,
How much signal reduction is there as the result of having the wrong circular polarization?
The difference between RHCP and LHCP is 20 dB
The difference between Horizontal and Vertical Linear is 20 dB
The difference between (RHCP or LHCP) and (Horizontal or Vertical) is 3 dB
If I understand right, you only get 3db extra when using CW/CCW but I have also read somewhere that you also lose 3db when running CW/CCW so why use Circulair polarisation and not just Horizontal or Vertical pol.
Ryan, NF0T
73's Jan / PE0SAT
Sent via [email protected]. 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
When deciding is Circular worth it, look at your local terrain. Reflections are the opposite polarity. If there are large buildings or mountains that create reflections as the satellite travels there will be a large amount of QSB from the add/subtract of the signal and the reflections at the antenna. Circular to circular reduces the reflections by more than 20dB, and also reduces rotational fading from the satellite spin. If you are out on a prairie or 20 miles out to sea you most likely will not need circular polarization.
Art, KC6UQH
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Angus Sent: Friday, September 19, 2008 1:19 PM To: [email protected] Subject: [amsat-bb] Re: Polarity questions
By having circular polarisation that matches the satellite (RHCP or LHCP but
the same polarity) you have very little QSB fading during the pass of the satellite. Using my own system I normally start a pass on Horizontal as the satellite is at AOS and then when it rises switch to the correct circular polarity and as the satellite gets near to LOS I am back on horizontal polarity with good quality signals through the entire pass. try listening to a NOAA weather satellite on 137mhz on a fixed polarity antenna i.e V or H and for some of the pass the signal is very good but as the signal changes polarity the signal drops down into the noise and through
the satellite pass you will get these peaks and troughs of signals. This is why if possible it is best to use circular or better still have the ability to switch polarity during the pass. regards Gus ----- Original Message ----- From: "pe0sat" [email protected] To: [email protected] Sent: Friday, September 19, 2008 7:02 PM Subject: [amsat-bb] Re: Polarity questions
On Fri, September 19, 2008 16:58, Ryan Butler wrote:
Tim Tapio wrote:
Hi Tim,
How much signal reduction is there as the result of having the wrong circular polarization?
The difference between RHCP and LHCP is 20 dB
The difference between Horizontal and Vertical Linear is 20 dB
The difference between (RHCP or LHCP) and (Horizontal or Vertical) is 3 dB
If I understand right, you only get 3db extra when using CW/CCW but I have also read somewhere that you also lose 3db when running CW/CCW so why use Circulair polarisation and not just Horizontal or Vertical pol.
Ryan, NF0T
73's Jan / PE0SAT
Sent via [email protected]. 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
Theoretically, it's 'infinite', but out in the real world, expect around 20~25dB loss from being completely cross-polarized. When I was doing commercial satellite work, if we could get 26~27dB we were happy, but this was with rigidly controlled satellites and commercial ground stations. Between linear and circular, expect about 3dB loss. Jim KQ6EA
--- On Fri, 9/19/08, Tim Tapio [email protected] wrote:
From: Tim Tapio [email protected] Subject: [amsat-bb] Polarity questions To: [email protected] Date: Friday, September 19, 2008, 5:58 AM Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
Sent via [email protected]. 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
A follow-up question --
I'd like to homebrew a circularly polarized antenna. Does anyone have a favorite relay switch to use for this application? A lot of them seem not to be weather-proof. It seems BNCs would make good connectors, but I'd be interested in opinions on this, too.
73, Bruce VE9QRP
On Fri, Sep 19, 2008 at 1:34 PM, Jim Jerzycke [email protected] wrote:
Theoretically, it's 'infinite', but out in the real world, expect around 20~25dB loss from being completely cross-polarized. When I was doing commercial satellite work, if we could get 26~27dB we were happy, but this was with rigidly controlled satellites and commercial ground stations. Between linear and circular, expect about 3dB loss. Jim KQ6EA
--- On Fri, 9/19/08, Tim Tapio [email protected] wrote:
From: Tim Tapio [email protected] Subject: [amsat-bb] Polarity questions To: [email protected] Date: Friday, September 19, 2008, 5:58 AM Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
Sent via [email protected]. 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 [email protected]. 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
----- Original Message ----- From: "Tim Tapio" [email protected] To: [email protected] Sent: Friday, September 19, 2008 2:58 PM Subject: [amsat-bb] Polarity questions
Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
Hi Tim, K4SHF
The above matter has been discussed many time on this BB by the way the following article is strongly recommended because it answere to your question with easy.
"The Advantages of Circular Polarization" by K4KJ Sept-12-1975 ARRL Technical Symposium, Reston Virginia
The above article is available in two zipped files on request off line to everyone is interested on it.
73" de
i8CVS Domenico
participants (11)
-
Angus -
Art McBride -
Bruce Robertson -
Edward Cole -
i8cvs -
Jim Jerzycke -
pe0sat -
Ryan Butler -
Sebastian -
SV1BSX -
Tim Tapio