circular polarization for mobiles....

[Gummybear]

Is it possible?

Do they even make a dual polarization ant's for mobiles?

Does anyone know about CP?


I am very interested in Cp for the moment. tried to post a pic but got this instead: Your images may only be up to 550 pixels wide. very un straight. this message is PC for the masses of cbrt.

['Doc]

For any half way normal mobile use, circular polarization would do you no good at all.
- 'Doc

[626]

Ok doc....

Why

['Doc]

Do you know of anyone else using it? And believe it or not, there's a left and right hand polarization. Which to use? How about losses from cross polarization? Vert/horz/circular? What benefit would there be? If your vehicle ever assumes a motion where circular polarization would be a benefit, oh are you in trouble anyway...
- 'Doc

[626]

Well, I was hoping for something a little more technical. Ive come to expect thorough posting from you Doc. Teach me what you know.

I understand the losses associated with receiving vertically polarized RF radiation on a horizontal antenna and vice versa. But, I am under the impression that circular polarization is received equally by vertical and horizontal antennas. Or, antennas that are both vertically and horizontally polarized like some field expedient dipole designs (inverted L). I realize that the aforementioned antenna is a base antenna.

In addition, I was hoping to hear your explanation on how the circular polarization is affected by "skipping" off of the ionosphere. Does it change polarization from this reflection?

Finally, your vehicle would have to roll very fast, on the order of Mhz to effect a circular polarization of Rf from a vertical mobile antenna.

???
GUNNY

['Doc]

And the biggy is the relative size of a circular polarized antenna for 27 Mhz on a mobile, along with the care and feeding of the thing.
I think you will find that most 'CP' antennas are very useful at VHF and above. Not so useful below VHF, primarily because of practical aspects. Can it be done? Sure. Is it practical? Sorry, no it isn't. At least, not on my truck. You wanna do it? Hey, knock yourself out!
- 'Doc


Sorry to disappoint you Gunny, but I've just never had enough of a use for a 'CP' antenna to learn much about them. I would have to look for information about them like most other people would. I know a tiny bit about them, but that's it.

[Red Warrior]

Let's consider three types of polarization, vertical, horizontal and circular. The first two seem to be well understood by this forum. The third, circular, can have two components, left hand circular and right hand circular. An antenna like a cubical quad can receive circular polarization and when used with a diversity combiner can theoretically result in a 3dB gain (under perfect conditions). For this gain to be realized both the transmitter and receiver must be operating in circular mode. Most CB folks encounter circular polarization as a result of the ionisphere changing the characteristic during skip conditions.

For a mobile to take advantage of this one would need to mount a horizontal and vertical antenna and use a diversity combiner to resolve signal ambiguity. The reason this is not commonly done is due to the difficulty in antenna construction to work in the mobile environment and the cost of diversity combiners.

Circular polarization and diversity combiners are common in satellite and military communications.

[Gummybear]

Thanks guys! I guess I will have to try harder to come up with something that is a actual improvement over a plain jane omni directional vert. ant.


Thanks Doc and red for explaining CP better. And thanks Gunny for pushing for a answer.

[626]

Thanks guys,

I appreciate the follow up. Hey 818 I talked to motormouth on the phone. One cool cat.

GUNNY

[Red Warrior]

Thanks guys,

I appreciate the follow up. Hey 818 I talked to motormouth on the phone. One cool cat.

GUNNY

Yep I like to call him Overkill. He is 100%.

[Gummybear]

Are there any antenna builder's willing to help me?

useful links: [Please login or register to view this link]
[ external image ]

[Gummybear]

What are your thoughts on this as well? The link tells about it.
[Please login or register to view this link]

[ external image ]

['Doc]

Opinion about the second example.

This one is designed for 87 - ?? Mhz use, and is about 1m x 1m x 1m in size. 27 Mhz is about 1/3 of that frequency, so will be about three times as large. So, about 9ft x 9ft x 9ft in size. I think that would be sort of 'pushing' it for a typical mobile antenna.
They didn't specify how they came about their gain figures so that sort of makes me wonder about them. For example, did they include that typical -1.? loss in gain because of the circular polarization thingy or not? If not, then the total loss is something like 3 dBd from the git'go. I'm just not too sure a reduction in 'fading' would be worth a 3 dBd loss, would it?

I'll make you a deal! If you will get other people to use them, and if you will pay for the materials needed, I'll make as many as you want. Oh yeah, it'll cost one '6-pack' per antenna! Howzat for a deal, huh? There'll be some upper limit on the number made, but I'll betch'a it'll be more than the number of people you can talk into using them on a mobile! Oh! No choice in the matter, every one of them will be painted pink!
- 'Doc

[Gummybear]

'Doc, you are a riot. I understand your point...way too big to drive around with. Do CP antenna's really have to be as big the ones I am finding?

I was under the impression that there are two different ways to achieve CP. Electric length and physical length. So if we satisfied the electric length like fiberglass whips do it could be a lot shorter right?

I understand that a out of step co phase harness is used to create left hand or right hand CP.( I am not perfectly clear on the math of this.) I understand that the radials have to be 90* apart in order to work as well. I am just not following why a smaller antenna can not be made to work.

I hope you can explain it as I would like to fully understand CP and how to make it. I would not mind having you make them, just not the 9x9 model. I would not care that it was pink either. I am one hell of a sell's men, at the age of 22 I became the outside sales Pro for a major company. I bet I could sell the 9x9x9x9x9x9 model to "dedicated" radio operators with the stipulation that every model be setup for RHCP. That way everyone will realize the benefits of CP.

['Doc]

...double post. Sorry 'bout that.

['Doc]

Size.
Basically it's the same problem as reducing the size of any antenna. At some point, the losses just out weigh any benefits. As in efficiency, or having the same radiation pattern, etc. What's that point? I have no idea. Size/length is always frequency dependent. Lots of things are practical in the Ghz ranges that are very impractical at HF.
Really wanna get 'fancy'? Try looking up a 'bifilar' or 'quadrafilar' antennas. They're typically classified as 'space craft' antennas, and are a bit more suitable than just 'plain' circular polarized antennas. They're circular polarized too, and not -that- much smaller, but some.
And if you are waiting for me to explain the physics of circular polarization, OH are you in trouble!
- 'Doc

Just for grins go look at this.

[Please login or register to view this link]

[Gummybear]

hey 'Doc, how about this idea? [Please login or register to view this link]


It is used for weather satellite stuff. I am not clear though on how the signal radiates from it but it looks cool...

['Doc]

Ah ha! 'Quadrifilar' antenna!
Scale it up from 137 Mhz to 27 Mhz. Close to 5x all dimensions. Keep reading, lots of fun to tune!
- 'Doc

[Gummybear]

Oh, and I am not looking for you to explain quantum physics to me, just CP.

I have been reading a lot about CP and understand what I think to be a decent amount on it now.

I would like to design a antenna that is for mobile purposes and maybe actually have some real world benefits, like CP would if everyone used it.

What would the quad. that I posted above look like size wise for 11 meter?

['Doc]

I figure it would be real close to the size of a 500 gallon hot water heater. Give or take 50 gallons or so, sort of. How am I supposed to know that stuff?

Each of those vertical 'elements' are a 1/4 wave length before being bent/twisted. Take it from there. I'm too lazy.
- 'Doc

[626]

Ok Gummy you wanna spin your head a bit? The antenna below is a DDRR antenna. It can be made quarter wave and is mounted horizontally above a groundplane. Get this.... IT IS VERTICALLY POLARIZED!!


Directional Discontinuity Ring Radiator.

[ external image ]

['Doc]

Gunny,
Just guessing from the picture, I'd have to say that DDRR was for UHF. One for 11 meters would probably be about the size of a car's roof, or a little larger, sort of. Ought'a fit good on top of a pickup's bed cover. Not exactly 'stealthy'. Might even be able to turn a luggage rack into one? they are about as effective as a typical 1/4 wave antenna, but not quite.
I read several articles about them lots of years ago, even thought I might try one. Hasn't happened yet. Oh well, lots of things I haven't tried yet.
- 'Doc

[Gummybear]

Keep them coming guys! I am loving this so far. Oh 'Doc, I emailed john something(figure to protect his identity) from the site of the quadriflar helicoidal antenna he said: Hi Samual...

Mobile on 11 meters? Wow, that would be quite spectacular!

It would measure about 4 meters (13 ft?) high, and 1.5 meters (5')
diameter. Of course it would be possible, but you'd have to take a lot of
care when passing tunnels and under trees

Seriously, it wouldn't make much sense, because quite surely, the other
party will have linear polarization (horizontal or vertical), and you'd be
throwing 30% of your power away.

John

So the way this is looking I am missing something...I mean how do other antenna companies make small antenna's???

[Gummybear]

I understand that whip's are wire wound around the fiberglass stick, so the wire is a lot longer than the finished product.

I understand that coils cut down on size, but are a compromise on performance. SO say I did try to make the quad. antenna mentioned above, If I added a coil to each beam then I could shorten it... but the coils would have to be taller than around as to not make contact with the other beams....Sounds like I am building a F***in wind chime....And who knows if the original function of CP would still work or if it would improve...

Any idea's? I want to build a mobile CP antenna, plain and simple.

['Doc]

... have you ever given any thought to FRS, or MURS, maybe?
- 'Doc