RCMF Donations

Enjoy using RCMF? How about a wee donation to help us keep you in the style to which you've become accustomed?

Welcome to RCMF. Please login or sign up.

July 02, 2020, 13:34:38 pm

Login with username, password and session length

Cloverleaf and Skew-planar antennas

Started by Mike_T, November 26, 2013, 00:45:36 am

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Mike_T

These appear to be the latest must-have for FPV applications. 

Any reason why they could not (or should not) be used on our tx's and rx's for normal control applications?

gtv

They are used on the video downlink which is normally 5.8ghz which has poor penetration and multi path problems, the skews help with this the it can reduce the range that is why we don't use thenon control, just the video. 


Phil_G

All 'gain' aerials work on a 'rob Peter to pay Paul' basis, meaning you cant have gain in one direction without losing signal strength in another.  An extreme example would be a high-gain yagi which would entail aiming it accurately at the model and following it throughout the flight because of the lack of signal just a few degrees off the beam.  Clovers work by flattening the 'donut' pattern, they remain omnidirectional but in a more 2-dimensional sense - the signal above and below the plane of the aerial is much reduced to give a greater omni-directional horizontal gain. 
Cheers
Phil

Mike_T

So, better coverage, but less overall range?

I'm aware of the 5.8G use for video - and the way range issues are overcome  :''

Phil_G

November 26, 2013, 12:16:23 pm #5 Last Edit: November 26, 2013, 12:20:03 pm by Phil_G
Only in the horizontal plane Mike, assuming the aerial is vertical.  A model directly above would see a very weak signal. You might think this is an unlikely occurrence but slope-soarers do it all the time!    The band makes no difference, 5.8, 2.4, whatever, the principle is the same, just the size of the aerial changes.

gtv


Mike_T

Quote from: Phil_G on November 26, 2013, 12:16:23 pm
Only in the horizontal plane Mike, assuming the aerial is vertical.  A model directly above would see a very weak signal


Doh!  Now I'm struggling to see the difference between a skew-planar's radiation pattern and the standard aerial's 'doughnut'.  From what you say Phil, it seems to me that there is little practical difference? $%&


Phil_G

November 26, 2013, 22:18:07 pm #8 Last Edit: November 26, 2013, 22:36:13 pm by Phil_G
To use the donut analogy, the diameter is made bigger by squashing it.
A steam-rollered donut if you like - wider than the normal radiation pattern (ie the gain) but less radiation in the arc above & below the horizontal than a standard donut:
[attach=1]
This is a side-on view of the radiation pattern. Straight out, the clover has more gain. At for example a 45 degree incline from the horizontal it has less. However from the top view, both have a circular pattern, ie both are omnidirectional.  This is very much simplified as its not actually a circle as there are 4 or 5 lobes (like petals?).  The other thing is the clover has circular polarisation - it doesnt matter if the receiving end is horizontal or vertical, though ideally its another clover.
Maybe one of the reasons its not used from the RC link is the number of nulls. The standard aerial has only one - end on. The clover has nulls between every lobe as well as end-
on.  Its swings & roundabouts, peter & paul  :af

Mike_T

Thanks Phil  :af

Given that the 'petals' overlap and are inclined, it would seem to me that this would help 'fill in' the nulls?

Also, the FPV guys appear to use a cloverleaf at one end and a skew-planar at the other (I really should google this, I know...)

Phil_G

November 27, 2013, 15:05:40 pm #10 Last Edit: November 27, 2013, 20:37:32 pm by Phil_G
yes, a true null is zero signal, in this case a null would show reduced signal, or no null at all with overlapping lobes.  But the gain in the horizontal plane is at the expense of the vertical component.  Perfect for model boats, cars and long distance (& hence low elevation) fpv models, not so good for a slope-soarer hanging into wind vertically above you!



onewinglow

December 03, 2013, 10:58:29 am #12 Last Edit: December 03, 2013, 11:07:07 am by onewinglow
The main reason for using these aerials is that the radiation patern is circularly polarised (CP 'right hand' or 'left hand') thus reflected signals are very significantly attenuated at the Rx as they are the opposite rotation to the transmitted signal. Their gain (?) is normally about 1dBi - 2dBi, much the same as a standard Rc Tx omni.
This may help http://beta.ivc.no/wiki/index.php/Cloverleaf_FPV_antenna
More if required.
HTH

Phil_G

December 03, 2013, 12:34:19 pm #13 Last Edit: December 03, 2013, 13:52:37 pm by Phil_G
Quote from: onewinglow on December 03, 2013, 10:58:29 am
The main reason for using these aerials is that the radiation patern is circularly polarised (CP 'right hand' or 'left hand') thus reflected signals are very significantly attenuated at the Rx as they are the opposite rotation to the transmitted signal.
Thats very true Allan and is a good thing for 'real time' analogue signals like video or voice.
Its all very interesting though and maybe worth a try, I might have a go as they're easy enough to make, then maybe try it in a disposable foamy!
Cheers
Phil

onewinglow

Phil,
Its been tried by some of the FPV community with no discernable improvements. The use of a centre fed halfwave on the Rx can show a slight range improvement over the commonly used free space quater wave. But, as normally the range of RC systems exceed the users eyesight there seems little point unless one wishes to fly (illegally) out of sight. If flying OOS then a directional Tx aerial, with gain, would be used as one would be flying in a limited area of sky and not be concered with beam width or low signal to the rear. Additionally, an improvement is to remotely mount the RC Tx aerial on an additional tracking unit paralleld up to the video Rx tracking unit.
I'm going too far off thread topic, time to stop.