Hi Andrew, That is exactly to be expected. 435.300 MHz is RHCP and 435.150 MHz is LHCP. Happy New Year 73 OZ1MY Ib ----- Original Message ----- From: "Andrew Rich" vk4tec@people.net.au To: "Amsat-Bb@Amsat. Org" amsat-bb@amsat.org Sent: Tuesday, January 01, 2008 10:12 AM Subject: [amsat-bb] 70cm Yagi and AO-51
Gudday
I tried a crossed offset yagi on the one boom.
When I threw just one part of the yagi on the boom, AO-51 was really good,
Now I am finding that with the second yagi on the boom I am seeing a big drop between 435.300 and 435.150 voice / data.
I think I might remove the second yagi from the common boom and add it to
a
new seperate boom
Comments ?
I think I am getting -20db due to the cross polar RHCP LHCP with the data
The voice is great , the data is down in the mud
--
Andrew Rich VK4TEC vk4tec@people.net.au http://www.tech-software.net
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
If I have this correct.
1. LHCP recieved on a RHCP can knock your signal down by some 20dB 2. LHCP matched with LHCP will result in a good signal.
So how does a linear antenna equate when receiving a circular signal ?
And the other way around, a circular receiving a linear signal ?
---------------------------------------------------------------------------- Andrew Rich VK4TEC
Andrew Rich kirjoitti:
So how does a linear antenna equate when receiving a circular signal ?
And the other way around, a circular receiving a linear signal ?
In the optimal situation there should be about 3dB attenuation. When circular is pointin off the other station the attenuation can be bigger.
Tnx for SKN qsos today for all Europeans.
Rolf Moberg oh6kxl
Hi Andrew, All,
First of all, Happy New Year!
A circular polarization is made of two orthogonal linear polarizations. This is why two crossed yagis (each one transmitting and receiving only linear polarization) realizes a circular polarized antenna. RHCP ad LHCP results by phase-shifting of + or - 90 degrees one of the two signals. If these two signals have exactly the same amplitude, and the phase shift is exactly 90 degrees we have an ideal circular polarized signal, this means that the so called "polarization vector" rotates on a perfect circumference. Of course this in reality is not possible, and our polarization many times can be like an ellipsis (or a potato HI).
So speaking practically, if your antenna has the wrong circular polarization (RHCP instead of LHCP) in theory you should not receive nothing! In reality, as the signal polarization has not a perfect circular shape, the actual attenuation can be as high as plenty of tenth of dB...
On the other side, if you use a linear polarized antenna to receive a circular polarized signal, you will loose one half of the power of the signal (no matters if right or left handed), as the circular polarization is made in equal parts by two linear polarized signals. So this means -3dB (At least, in theory...).
Last but not least, if you use a circular polarized antenna to listen to a linear polarized signal, you won't see any difference than using a linear polarized antenna. In this case you can have an advantage, as the signal polarization can even rotate during its travel, so you'll not have additional losses.
Hope this helps.
Happy 2008 to All.
73s
Simone - IW1FYV
2008/1/1, Andrew Rich vk4tec@people.net.au:
If I have this correct.
- LHCP recieved on a RHCP can knock your signal down by some 20dB
- LHCP matched with LHCP will result in a good signal.
So how does a linear antenna equate when receiving a circular signal ?
And the other way around, a circular receiving a linear signal ?
Andrew Rich VK4TEC
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
3-dB down each way. For satellite reception this is not too bad. However, some satellite's circular pol (CP) signals are elliptical (have some linear component) if they have a squint angle with the ground station. Thus the use of the linear-pol Arrow and the "Arrow Wave" works quite well.
In the past being able to switch sense in CP helps because satellite squint can result in a reverse of polarity sense. Then you have AO-51 that utilizes opposite sense CP on different frequencies to improve isolation in the onboard receivers.
HNY & 73, Ed - KL7UW
At 06:54 AM 1/1/2008, Andrew Rich wrote:
If I have this correct.
- LHCP recieved on a RHCP can knock your signal down by some 20dB
- LHCP matched with LHCP will result in a good signal.
So how does a linear antenna equate when receiving a circular signal ?
And the other way around, a circular receiving a linear signal ?
Andrew Rich VK4TEC
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
73, Ed - KL7UW ====================================== BP40IQ 50-MHz - 10-GHz www.kl7uw.com 144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w DUBUS Magazine USA Rep dubususa@hotmail.com ======================================
Andrew, Theoretical circular to linear loss is 3dB either LH or RH vs any angle of linear polarization. A linear polarized antenna rotated in the field of a circular polarized wave will show no change with rotation. The amount of variance that is measured on circular antennas comes from the pattern of the circular antenna being elliptical and not circular. This is refered to as the axial ratio and in practice anything less than a 3 dB varance is considered good. A standard helix antenna is typically 4-5 dB. This is a +/- value in addition to the 3 dB loss for cir to lin conversion.
Art KC6UQH ----- Original Message ----- From: "Andrew Rich" vk4tec@people.net.au To: "OZ1MY" oz1my@privat.dk; "Amsat-Bb@Amsat. Org" amsat-bb@amsat.org Sent: Tuesday, January 01, 2008 7:54 AM Subject: [amsat-bb] Re: 70cm Yagi and AO-51
If I have this correct.
- LHCP recieved on a RHCP can knock your signal down by some 20dB
- LHCP matched with LHCP will result in a good signal.
So how does a linear antenna equate when receiving a circular signal ?
And the other way around, a circular receiving a linear signal ?
Andrew Rich VK4TEC
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
----- Original Message ----- From: "Andrew Rich" vk4tec@people.net.au To: "OZ1MY" oz1my@privat.dk; "Amsat-Bb@Amsat. Org" amsat-bb@amsat.org Sent: Tuesday, January 01, 2008 4:54 PM Subject: [amsat-bb] Re: 70cm Yagi and AO-51
If I have this correct.
- LHCP recieved on a RHCP can knock your signal down by some 20dB
- LHCP matched with LHCP will result in a good signal.
So how does a linear antenna equate when receiving a circular signal ?
And the other way around, a circular receiving a linear signal ?
Andrew Rich VK4TEC
Hi Andrew, VK4TEC
Read please my article "Switching four Polarizations on a 70 cm Crossed Yagi"
Part-1 in AMSAT-Journal March/April 2007 Part-2 in AMSAT-Journal May/June 2007
Switching from Horizontal to Vertical and from RHCP to LHCP from the shak using 4 small coax relays antenna mounted you will get the better polarization match between the signal actually received from the satellite and your antenna system. In addition mounting the elements in X configuration over the boom you get Horizontal and Vertical polarizations for best performance in tropo communications.
If you cannot find the above articles please let me know.
73" de
i8CVS Domenico
participants (7)
-
Andrew Rich -
Edward Cole -
i8cvs -
kc6uqh -
OZ1MY -
Rolf Moberg -
Simone T