At 09:23 AM 9/20/2008, n3tl@bellsouth.net wrote:
I don't-at-all disagree with the concept that working AO-27, AO-51 and SO-50 isn't terribly difficult with a handheld station. Frankly, that has really (and pleasantly) surprised me. However, I do believe that adjusting polarity when hand-holding the Arrow provides improved performance during many passes.
It makes a big difference in many cases.
73 de VK3JED http://vkradio.com
On Sep 19, 2008, at 11:24 PM, Tony Langdon wrote:
At 09:23 AM 9/20/2008, n3tl@bellsouth.net wrote:
I don't-at-all disagree with the concept that working AO-27, AO-51 and SO-50 isn't terribly difficult with a handheld station. Frankly, that has really (and pleasantly) surprised me. However, I do believe that adjusting polarity when hand-holding the Arrow provides improved performance during many passes.
It makes a big difference in many cases.
I'm kinda sitting here chuckling that people have "opinions" on how physics works. :-)
Tony's right: Of course polarity makes a difference. It's well proven physical science at this point in our RF history.
When the physics don't match the real-world experience, look for variables that might be affecting the test.
For example, most FM receivers aren't linear in their response from "noisy" to "quieting" on weak-signals.
If the satellite is moving, rotating, and generally "messing up" the test, it's hard to always see the results of polarity changes -- mix in trying to do it by hand, and different people's tolerance for listening through noise, different receiver sensitivities, higher and lower gain antennas, and pretty soon -- the whole test is pretty non- objective.
Some people may say "not switching polarity works fine" and on a particular day, with a particular rig, antenna, satellite orientation or motion, and a different set of between the ears DSP filters (ears) than the next person, their perception may be accurate for their experience -- but it doesn't change the physics... 20 dB loss is still 20 dB of loss due to a polarity mismatch.
This is just the difference between the practice of radio communications, and the hard science of it all...
-- Nate Duehr, WY0X nate@natetech.com
On 20 Sep 2008 at 0:56, Nate Duehr wrote:
This is just the difference between the practice of radio communications, and the hard science of it all...
Or it is the difference between the engeneers and the real world...lets say they are right and the world have to adapt and when something goes wrong it's not an error by a faulty application of their plans.
I will soon have 2 41 elements 2.4ghz beam installed one vertical the other horizontal and i will be able to switch between them. On 2.4 AO- 51 there is a strong QSB effect is it coming from polarity change? or from the satellite thumbling? Could be i will be able to eliminate one variable.
Did any one try to feed 2 antennas through a splitter with one vertical and the other horizontal? Is this can solved this polatity question?
"-"
Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe WAC BASIC CW PHONE SATELLITE
At 01:53 AM 9/20/2008, Luc Leblanc wrote:
On 20 Sep 2008 at 0:56, Nate Duehr wrote: ======snip
Did any one try to feed 2 antennas through a splitter with one vertical and the other horizontal? Is this can solved this polatity question?
"-"
Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe WAC BASIC CW PHONE SATELLITE
Sent via AMSAT-BB@amsat.org. 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
Luc if both antennas are identical and have equal length feedlines to the splitter, the result is slant polarization (linear pol slanted at 45-degrees if one antenna is vertical and the other horizontal). You are better running each antenna to a coaxial switch and chosing either one (not both).
73, Ed
On Sep 20, 2008, at 2:07 PM, Edward Cole wrote:
At 01:53 AM 9/20/2008, Luc Leblanc wrote:
On 20 Sep 2008 at 0:56, Nate Duehr wrote: ======snip
That was a weird snip... made it look like my comments were left in that question and statement from Luc.
I do have a question for the polarity gurus, however...
When *transmitting* circular vs. linear polarity, are the apparent losses the reverse of the numbers being used for receiving? I am inclined to think that has to be true.
Or to put it as a question: With all else being equal, including antenna gain numbers...
How much more power has to be put into a circularly-polarized antenna versus a linearly polarized one of the same gain, to have a distant station receive the same signal if they're linearly polarized?
I'm purposely coming at this from the "other" direction... the transmit side, instead of what is seen at the receiver.
This is mostly a mental exercise to see if I "get it". So if it's a goofy way to analyze it, ignore that for a moment...
-- Nate Duehr, WY0X nate@natetech.com
At 02:29 AM 9/21/2008, Nate Duehr wrote:
... I do have a question for the polarity gurus, however...
When *transmitting* circular vs. linear polarity, are the apparent losses the reverse of the numbers being used for receiving? I am inclined to think that has to be true. ...
How much more power has to be put into a circularly-polarized antenna versus a linearly polarized one of the same gain, to have a distant station receive the same signal if they're linearly polarized?
Hi Nate,
This is a perfectly good question, Try this:
Let's say you have a horizontal RX antenna down range.
At the TX side, you have a horizontal and a vertical antenna and they are quadrature phased so they make circular polarization.
Now your tx can put out 100 watts. The 100 watts gets split equally between the horizontal and vertical antennas so you are putting 50 watts into the horizontal and 50 watts into the vertical.
The RX antenna down range doesn't know you are sending circular! Since it is horizontal, it only responds to the horizontal signal. It doesn't even see the vertical signal and it couldn't care less about the phasing. It sees the 50 watts you put into the horizontal antenna. The 50 watts you put into the vertical antenna is just wasted.
Now imagine you disconnect the vertical TX antenna and put all 100 watts into just the horizontal antenna. Now the RX antenna down range sees the 100 watts you put into the horizontal antenna versus the 50 watts you did before so you are up 3dB.
So, circular to linear, you wasted half your power and you lose 3dB.
Any good?
73, Tony AA2TX
Nate, The advantages of circular when both antennas are circular is not the 3 dB gain, but the ability to except the rotation of the antenna without signal change and cancellation of the first reflection (reduction of multipath fading) which produces steady signals. Yagi types are subject to receiving reflections from the side and are only circular polarization on the on axis lobe. Off axis reverse circular rejection is limited to the forward gain and side lobe rejection of a Yagi antenna. Helix and QFH antennas are circular over the entire envelope. The use of dish reflectors on frequencies of 1.2 GHz and above is recommended. There are several designs, one in an old AMSAT Journal of a patch feed and polarity switch that works well as a RH/LH circular feed for the popular TVRO satellite dishes that are abundant.
Art, KC6UQH
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Nate Duehr Sent: Saturday, September 20, 2008 11:29 PM To: AMSAT BB Subject: [amsat-bb] Re: Polarity questions
On Sep 20, 2008, at 2:07 PM, Edward Cole wrote:
At 01:53 AM 9/20/2008, Luc Leblanc wrote:
On 20 Sep 2008 at 0:56, Nate Duehr wrote: ======snip
That was a weird snip... made it look like my comments were left in that question and statement from Luc.
I do have a question for the polarity gurus, however...
When *transmitting* circular vs. linear polarity, are the apparent losses the reverse of the numbers being used for receiving? I am inclined to think that has to be true.
Or to put it as a question: With all else being equal, including antenna gain numbers...
How much more power has to be put into a circularly-polarized antenna versus a linearly polarized one of the same gain, to have a distant station receive the same signal if they're linearly polarized?
I'm purposely coming at this from the "other" direction... the transmit side, instead of what is seen at the receiver.
This is mostly a mental exercise to see if I "get it". So if it's a goofy way to analyze it, ignore that for a moment...
-- Nate Duehr, WY0X nate@natetech.com
_______________________________________________ Sent via AMSAT-BB@amsat.org. 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
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Great answers guys... that made it perfectly clear!
Nate WY0X
----- Original Message ----- From: "Luc Leblanc" lucleblanc6@videotron.ca To: amsat-bb@amsat.org Sent: Saturday, September 20, 2008 11:53 AM Subject: [amsat-bb] Re: Polarity questions
I will soon have 2 41 elements 2.4ghz beam installed one vertical the other horizontal and i will be able to switch between them. On 2.4 AO- 51 there is a strong QSB effect is it coming from polarity change? or from the satellite thumbling? Could be i will be able to eliminate one variable.
Did any one try to feed 2 antennas through a splitter with one vertical and the other horizontal? Is this can solved this polatity question?
"-" Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe WAC BASIC CW PHONE SATELLITE
Hi Luc, VE2DWE
A two port power splitter 1/4 wavelenght electrically long at 2400 MHz with characteristic impedance of 36 ohm is only 31 mm long and probably due to the intrusion for the lenght of three N connectors will not make the impedance transformation between 25 ohm of both antennas in parallel to 50 ohm of your transmission line.
If you have available a 1/4 wavelenght two port power divider for 435 MHz you can readily use it as a quik test because 2400 / 5 = 480 MHz wich is not too much far away from 435 MHz
Since the ratio by 5 is an odd numbar then the impedance transformation between 25 ohm to 50 ohm can be accomplished with a small increase in VSWR
If the above test is encouraging then you can cut the above 435 MHz power divider to resonate exactly at 480 MHz.
To get CP don't forget to make one coax line 1/4 electrical wave longer than the other one or to shift one antenna 1/4 wave free space behind the other one with respect to the satellite...........a very difficult affair at these frequencies.
In my opinion it would be better to use two helix antennas one RHCP and the other one LHCP switching polarity with only one coax relay.
Have fun
73" de
i8CVS Domenico
Luc, You loose 3 dB if you are not circular. Phasing YAGI antennas at 2.4 GHz is very difficult, YAGI antennas must be identical and have the exact same phase center. You would be better off to use a 18" dish and a patch feed, or a helix. I am not sure that AO-51 is circular polarized on 2.4 GHz. Art, KC6UQH -Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of i8cvs Sent: Saturday, September 20, 2008 4:54 PM To: Luc Leblanc; AMSAT-BB Subject: [amsat-bb] Re: Polarity questions
----- Original Message ----- From: "Luc Leblanc" lucleblanc6@videotron.ca To: amsat-bb@amsat.org Sent: Saturday, September 20, 2008 11:53 AM Subject: [amsat-bb] Re: Polarity questions
I will soon have 2 41 elements 2.4ghz beam installed one vertical the other horizontal and i will be able to switch between them. On 2.4 AO- 51 there is a strong QSB effect is it coming from polarity change? or from the satellite thumbling? Could be i will be able to eliminate one variable.
Did any one try to feed 2 antennas through a splitter with one vertical and the other horizontal? Is this can solved this polatity question?
"-" Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe WAC BASIC CW PHONE SATELLITE
Hi Luc, VE2DWE
A two port power splitter 1/4 wavelenght electrically long at 2400 MHz with characteristic impedance of 36 ohm is only 31 mm long and probably due to the intrusion for the lenght of three N connectors will not make the impedance transformation between 25 ohm of both antennas in parallel to 50 ohm of your transmission line.
If you have available a 1/4 wavelenght two port power divider for 435 MHz you can readily use it as a quik test because 2400 / 5 = 480 MHz wich is not too much far away from 435 MHz
Since the ratio by 5 is an odd numbar then the impedance transformation between 25 ohm to 50 ohm can be accomplished with a small increase in VSWR
If the above test is encouraging then you can cut the above 435 MHz power divider to resonate exactly at 480 MHz.
To get CP don't forget to make one coax line 1/4 electrical wave longer than the other one or to shift one antenna 1/4 wave free space behind the other one with respect to the satellite...........a very difficult affair at these frequencies.
In my opinion it would be better to use two helix antennas one RHCP and the other one LHCP switching polarity with only one coax relay.
Have fun
73" de
i8CVS Domenico
_______________________________________________ Sent via AMSAT-BB@amsat.org. 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
__________ Information from ESET NOD32 Antivirus, version of virus signature database 3458 (20080921) __________
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At 04:56 PM 9/20/2008, Nate Duehr wrote:
Tony's right: Of course polarity makes a difference. It's well proven physical science at this point in our RF history.
Indeed. :)
If the satellite is moving, rotating, and generally "messing up" the test, it's hard to always see the results of polarity changes -- mix in trying to do it by hand, and different people's tolerance for listening through noise, different receiver sensitivities, higher and lower gain antennas, and pretty soon -- the whole test is pretty non- objective.
Well, I had a pretty good way of determining polarisation. I used to hand rotate the antenna through 180+ degrees, and there WAS a definite peak and null, as you'd expect. This required frequent adjustments, as the polarisation would shift significantly during a pass.
Some people may say "not switching polarity works fine" and on a particular day, with a particular rig, antenna, satellite orientation or motion, and a different set of between the ears DSP filters (ears)
I can copy just about anything this side of white noise, but if I can improve the signal, I will. :)
73 de VK3JED http://vkradio.com
participants (7)
-
Anthony Monteiro -
Art McBride -
Edward Cole -
i8cvs -
Luc Leblanc -
Nate Duehr -
Tony Langdon