900Mhz turnstile on video tx?

[Holski77]

The turnstile is a great antenna, so why is it only used for UHF mostly?
Its low profile makes it great for flying wings.
I should be able to make one for my video transmitter without any trouble right?

I am thinking that a SPW would be good on the receiver, crosshair or helical for a directional?

[iPeel]

Firstly, I'm not sure that it is a great antenna. IBCrazy brought it to the RC community and confesses himself that he mostly uses Dipoles and that they outperform the turnstile, he only uses a turnstile on one of his planes and it's not a long range airframe. Sure the antenna fits nice and snug against the body of the plane, but that does't make it the greatest at receiving signals as it is likely to run close and parallel to carbon spars / servo wires / noisy supply rails etc. You are better off having an RX antenna which holds itself away from stuff like that and presents itself proud of anything that could get in between it and the line of sight to the transmission.

Secondly, I think the turnstile is an antenna best suited for reception, not transmission. You are talking about using it on a TX?

Thirdly, it would not be a good antenna for reducing reflections, which is why people use CP antennas.

In conclusion, I think it would be a bad choice for a VTX antenna, you are much better off with a Skew / Bluebird / Mad mushroom / other CP antenna.

[Holski77]

It is possible though?

Correct me if I am wrong but i thought a turnstile was a CP antenna.

I think there would be a niche for this antenna, especially around the lower frequencies where external antennas become larger.
I am just looking to compromise a little on 900Mhz impressive range while achieving easy 5.8 form factor.
I realize that a lot of people don't have any problem with large external antennas and neither do I.

But, when it comes to the impressive directional receiver antennas people are making today, your could pick up a video signal from a rubber ducky from an impressive distance, why not a turnstile? Turnstiles avoid polarizations issues and multipathing, and a good helical could reach out and grab the signal.

What makes it a bad transmitter antenna? Is it too hard to match the SWR?

Because IBcrazy is nice enough to post instructions that a monkey like me could follow, I have made some 1040 blue beams myself and they brought me to a mile on HK fpv gear. But as I am building my 3 turn helical, I can't help but think of other options. Doing it from scratch, a turnstile would be a lot easier to construct than another cloverleaf or SPW.

[iPeel]

No, the turnstile is a horizontally polarised antenna in it's designed orientation, it's not a circular polarised antenna.

[Coyote]

Well yes and no, the Turnstile is LCHP and RHCP at the same time due to the sequence delays the signal comes out from each corresponding dipole, although its used normally with a linear receiver antenna because its not true circular.

[Holski77]

:o Mind blown

So there is almost no benifit to using circular/linear on the other end?

[Coyote]

There is ........... But it comes with a price.

If you had circular on the plane and linear on the ground you could then bank the plane and instead of getting breakup ( up to -26dbi ) you get with linear you would get no loss so no break up in the picture.

The pay off is you would loose 3dbi straight away which is quite a lot, then you would loose multipath rejection that circular to circular give you