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
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