Antenna cross polarization loss demonstration
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- Опубліковано 29 вер 2024
- This is a quick video demonstrating cross polarization loss with linear and circular antennas. Marc (FPV Goose) came up with this test set up to measure element orientation after the antenna covers were installed and it really shows how well the system works.
I love these type of videos Alex, can you make more educational videos on antennas and all the mysteries of how they work?
I gotta question about fpv on water. Fpv boat specifically. What are your thoughts on best frequencies and antenna's for control and fpv on water where you have a fixed height but want to get some range?
This is where linear shines! That system I had on my test bench is perfect for this. An HD dipole (which consequently works well for analog and is super cheap) coupled with a BiQuad does really well.
Thanks for the reply. I will do a test when i get my boat finished with CP and linear. At the moment the only linear ones i have are rubber duckies.
of course, because especially if you're on salt water, that becomes the other half of the antenna... a friend of mine who used to live on the intracoastal down here in florida, had a hbtv5 at the end of his dock and WOW .... his rx was a huge improvement..... now of course this is for even lower frequencies 20/40/80m but the same rules still apply to some degree... having a real dipole antenna is always better than a monnopole where it's using the vtx as the other half of the antenna
What's the antenna to the right? He said "linearly polarized hd dipole" I think? But I can't find something named like that online. Looks like a sleeve dipole maybe?
And that's why I put my linear antenna on a gimbal with it's video transmitter. Now it's always straight up and down.
Is there any reason for not running a circularly polarized antenna on a rc transmitter all the time besides size and fragility?It looks like it is a no-brainer but i have never seen anybody doing it other than you.
I have found using CP on control yields great results. If you can deal with the size, use a CP omni.
Thanks for your answer.I am going to build a spw for my transmitter.
Awesome as usual Alex, thank you!
thanks for the video
You have some good videos. I am an EMC engineer so naturally want to nitpick some of the things you are doing with the analyzer. Overall though I really like your show.
thank you very much ....it helped me a lot understanding about polarization.
Nice video Alex. Thank you for the demonstration.
CP antenna for the crossfire? would it be too big?
hi Alex, great vid explanation as usual, may I know what VNA is that? is it FieldFox agilent as you used before?
Yes. Same Agilent Field fox.
Now overlay some AR on that bish.
Thanks for sharing You B Crazy now.
Hi, I was wondering how the antenna would still be able to receive anything when tx is vertical and rx is horizontal. The electrons of the receiver would only move up and down, but not left and right. So they would not create a current.
You ask a devastating key question, well done.
If both the transmit and receive antennas are ideal (e.g. zero thickness wires, perfect-shaped horn made of zero thickness metal, etc.) then yes the crosspolar voltage gain would be 0 (-infinity dB). Expect real-world antennas to support some surface currents in the orthogonal plane.
The issue is more interesting when a collimating reflector is involved.
Off-axis reflectors can also couple a crosspolar signal to a copolar signal; imagine an off-axis passive wire oriented at 45 deg illuminated by V-pol or H-pol. The wave scattered by the off-axis wire will have 45 deg polarization, thereby coupling to both V-pol and H-pol.
So if you have a linear on the TX side, you either need to fly upright all the time, or use a circular on the RX side and get lesser signal loss when off angle? This would explain why the dipole TX antenna has been working so much better than expected with circular on the goggle / RX side.
Is there any advantage to Left vs Right circular on the RX side if the TX is Linear? I've been running LHCP just figuring it would better reject the RHCP signals that most of the other pilots are transmitting with. The reality is I don't notice a significant difference. The omni is a Mad Mushroom on the RCHP setup and an Airblade on the LHCP setup.
You can certainly bank and turn. it is steep banks where the signal gets weak... and even then, unless you also point the null at yourself you are usually ok.
The circular on the goggle is likely working better simply because of the cross polarization issue if I had to venture a guess.
So when will you test a model reciever with a CP antenna? I would assume that the rssi wouldn't fluctuate as much with it.
For the most part, yes.
Is this effect reduced for lower frequencies? Like 1280 MHz?
It is changed. Not necessarily reduced, though.
what about running a dipol vertically... wouldn't that be cool... I mean the left right bank would still hurt but with quads that leaning forward for speed that would be a big win since the "how much tilt will I be at most of the time" question would be irrelevant, right? :)
For the most part, yes. However, you still have the multipathing issue to fix.
Sort of. The tilt of the antenna needs to be 90 degrees off from the camera to retain vertical orientation. Quads do not bank like airplanes, so this is less of a problem. However, many quads run at a 45 degree angle of attack and if you figure the radiation plot of the antenna as well as the 3 db polarization loss, that can result in 20% signal strength.
Thanks again IBC
This gets more confusing by the day. If you had to choose only one type/model of antenna to fly around a wooded area, what would it be?
Ions. Hands down the best for woods flying. On the RX, I'd run a Crosshair. If not possible, then an Ion again.
IBCrazy, what about in the other hypetrain where you use linear antenna (they call it snowman) for their VTx and use CP antenna for their VRx?
There are rare occasions where mixing CP and LP is beneficial. However, in most cases, it is better to use the same polarization on both ends.
I've always felt that a linear transmit and high gain CP Rx antenna like the Crosshair is the best way to go if you want a super light Tx setup. I run a small piece of 30AWG wire as an antenna and my video is fine =P
Top, thanks A.
If I'm running diversity. Should I use two linear or one linear and one circular.
I would just stick to one type of polarization, linear or circular. I see no reason to mix them.
Ill just use two dipoles on my receiver if im using one on the tx.
What about Connex and MIMO? Would you recommend the linear or CP version of your panel antenna for racing? The digital signal also benefits from multi pathing, so that complicates things even more.
Connex and MIMO are different... sort of... I have played with CP and LP for the Connex and found that the linear goes significantly farther. However, the clarity and ability to fly behind objects and trees is far better with circular. Mixing them doesn't work well on the connex.
Do you do transmit with both RHCP and LHCP or consistent all the way through? That's the kind of info I was looking for, thanks for the response!
I just stick to one polarization type (usually LHCP). There is a rare scenario to mix them to bend a signal around a corner, but I almost never use this.
great video Alex. Do you have any solutions to replace a linear antenna with an omnidirectional? I just got a baby hawk and it's a ton of fun. But I would like a better antenna on it. I can solder really well if I have to solder on an antenna myself
he sells cloverleaf antennas soldered to coax, and all youd have to do is cut the coax, then solder it to fit onto the baby hawk vtx. at least thats what i would do
cookie4524 ,Hey thanks for the info. I'll have to check RMRC for it.
I miake a micro antenna with a small cable for this. Tiny Whoop and RMRC sell it.
Thanks Alex! That is by far the best visual explanation I've ever seen. Keep doing what you do.