An Introduction to Circular Polarization (
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- Опубликовано: 21 мар 2024
- I was asked on a livestream to talk about the circular polarization of radio waves. Watch to learn more about the confusing and complicated topic of circular polarization, how it effects antennas and gets effected by the ionosphere.
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#amateur radio
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#antenna
#CircularPolarization
#polarization
#ionosphere
#radiowaves
#magneticfield
#eletricalfield
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Easy to understand explanation of polarization. A subject not usually addressed on ham radio RUclips channels. Thanks again for another great video
Much appreciated!
You did a great job Dave, explaining a very complex topic. I'm now reading the ARRL's book "Propigation and Radio Science", it's a great way to get drowsy, but also very interesting at times. Your depth of knowledge is often astounding.
This is one of the most interesting Ask Dave videos! Great topic, and explained well. Thank you.
Glad you enjoyed it!
Thanks Dave. This is quite helpful.
Great and informative video as always, Dave! If I may add a note from the broadcast radio world, the most common place you'll experience circularity polarized signals (in the U.S. at least) is FM radio. Originally FM broadcasts were horizontally polarized, but when car radios began including FM in the 1960s, they realized vertical polarization would have been better for both multipath interference and for the car's antenna placement. But horizontal was already the standard. The solution? Circularly polarize the signal! Car radios could use a vertical antenna, home receivers could keep using horizontal rooftop antennas, and portable radios could position the antenna any way that was convenient, just as you describe receiving skywave signals. Some common types of FM transmitting antennas producing circular polarization include the double-crossed dipole, the ring and stub, and occasionally the Lindenblad. Building one of these antennas might be a fun experiment for hams using 2 meters.
The BBC in the UK has the same problem and did a lot of research into this in the 1960s to 1980s. As in the US, horizontal polarisation was originally chosen, partly due to its greater immunity to ignition interference from cars from the 1940s-50s! However, car radios and portable transistor radios with vertical antennas forced a rethink. Interestingly, they did not pick a circular polarisation path but a 'mixed polarisation' path where both horizontal and vertical polarisations are transmitted but without the guaranteed 90 degree phase difference. There are a few BBC research papers on the subject that have been released and are publicly available.
Thanks to both of you for the information. The history adds a nice perspective. 73 from Dave
I remember back in the 70s we did not know the difference between right hand and left hand circular polarization.
Back then, I had not even heard of circular polarization. 73 from Dave
Back in the 50's we were glad to get our home made rigs to work. Being made on a wooden base and junk parts from old radios.
I do remember those days. I my first real transceiver was a Heathkit hw16. All tubes, of course. By the time I got my general, the Japanese Invasion was well underway. I Purchased a Yaesu FT 201. Nice Radio, with just three tubes.
📡 Your Way Too Ham Wise 📡
😎Thanks From Rick KN6UTF😎
You’re welcome. 73 from Dave
Many amateur satellites radiate circular polarization, and the number is growing. For example, the IO-117 satellite radiates circular polarization (RHCP). Right Hand Circular Polarization (RHCP) is the standard. Dave is incorrect when he says that the ground station needs to transmit LHCP to communicate with a RHCP satellite. Does the tread on a screw change polarization when viewed from the other end? Another point is that all polarization is elliptical. Linear and circular are just two special types of elliptical.
I Disagree. Let’s take the example of a screw being screwed into a piece of wood. Think of a simple spiral antenna. One transmitting, you point your thumb in the direction of the traveling wave. On transmit that is the opposite direction in which it receives. So it transmits say left-hand circular polarizationBut it will receive right hand circular polarization.
Well explained and good video. Question, how does a loop antenna polarize? 73, KF0NNQ.
Loop antennas have linear polarization. You can choose whether vertical or horizontal by where you feed it. You can find more explanations about this in the antenna book or online. 73 from Dave
Is there such a thing as a broadband circularly-polarized receiving antenna? The crossed-antennas trick requires picking a specific frequency (or at least a band), but can we replace the passive 1/4λ phasing stub with something active? For that matter, are there any transmitters that will do the phasing in-radio, letting you use two runs of coax to the antennas, and do the phasing either digitally or with some other electronics?
Yes, there are "broad" band CP antennas. For example, a Helix antenna is CP and with a relatively broad (2:1) bandwidth. There are even omnidirectional CP antennas, such as the Quadrifilar (QFH) helix antenna. There are phasing networks for antenna systems that allow the use of multiple antennas and phase adjustment. See the MFJ-1026. (This unit is intended to do noise canceling but can just as easily do signal addition.)
@@RB9522I guess by 'broadband' I actually mean 'multiband'. I don't have the space to put up four different antennas...
The antennas themselves could be fans or enlist traps, but the 1/4λ is a bit of an obstacle when trying to get the same antenna to do both 40 and 10...
I do have a Loop on Ground, which is very much horizontally polarized, and a "QRM remover" which doesn't help much with problems at my QTH, but perhaps if I lofted a second loop and used the QRM remover as a phase adjuster, I could read weaker signals better.
Thank you. N0QFT Glen