Windsurfer

[N017RW]

IMO, the only function the parabolic reflector does is to block other unwanted interferences around the RC's antenna. Yes, it does boost the signal, but all it does is to reflect noise towards the AC, so, it's only boosting noisy signal.
This is becuase there is a gap of 1-2 cm between the reflector and the anetenna, which is enough to throw the reflected signal out-of-phase from the direct signal transmited between the Tx and Rx. (Out-of-phase signal = noise).
I think it really depends on where you are using it, it's probably more effective in an urban setting than in the middle of wilderness.

The focal point (or in this case 'plane') is a function of the parabola's dimensions. It is independent of the frequency (wavelength).
GENERALLY all r/c antenna systems are subject to multi-path and some use this to their advantage with spatial diversity and/or MIMO configurations.

 

[dchao]

it's the 5.8g one the wind surfer is sitting on.
mimo assums you have more than one antenna, our 5.8g tx has only one, there is no spatial diversity.

 

[N017RW]

Diversity, MIMO... It's an example of using multipath to an advantage.

The parabolas, if properly designed and placed collect and focus the photons just like some flashlights do (such as Maglites).

 

[Paul Sw]

The windsurfer is just a parabolic reflector and becomes part of the antenna system. It concentrates the beam in one direction instead of the donut shape from the stock vertical dipole. The distance from the dipole to the reflector should be ¼ wavelength or about 3cm. The wave travels ¼ wavelength toward the reflector, is reflected with a ½ wave phase shift and travels ¼ wavelength back to the dipole where it combines, in phase, with the forward going wave. It does not “concentrate noise”.


As far as directivity is concerned, many seem to greatly exaggerate the amount of directivity, that is how accurately you must point the controller at the A/C (aircraft). The beamwidth is usually defined as the angle between the two points where the signal drops to one-half, or 3db. It is given, in degrees, by the equation 60 X Wavelength / dimension of antenna. Thus for an 8 cm antenna the half-power beamwidth is 60 X 12.5cm / 8cm = 94 degrees, hardly a “spotlight as opposed to a searchlight”. Although you must face is the direction of A/C and not turn your back.


The increased range to be expected from a windsurfer can be calculated from its increased gain. At best, it takes the radiation that would be transmitted behind you and combines it with the forward radiation, possibly doubling the signal strength toward the A/C. Since the signal always falls off as the square of the distance, if the signal doubles you would get the same signal at a range sqrt(2) further or 1.2 further. A 20 % increase in range seems to be about what most report.

Paul

 

[N017RW]

The dipole or active element needs to be at the parabolic focal point or plane when using a WS.

It is completely independent of wavelength.

However the parabola design should allow the distance between the active element and reflector to be several wavelengths when possible for maximum efficiency.

Due to the size constraints with the r/c controller it may not be possible to achieve maximum design efficiency.

Again there is no wavelength specificity for a parabola, it is the FOCAL point which must be observed for maximum efficiency.

All waves entering and reflected to the focal point will be in phase.

 

[Paul Sw]

You are exactly correct that the dipole must be at the focal point. I was really responding to post #19 where he thought the gap between the dipole and reflector created noise because of out of phase reflections.

 

[Kevinisme]

DIY your own 1 to test...

 

[solentlife]

If 'dchao' was right - which we know he isn't ... it would mean that we can throw away all our Satelite TV dishes ... digital internet dishes .... as well as our 'Windsurfers' !!

Oh and also the military and commercial direction finding gear !!

I had range increase from about 600m to over 1500m .. on good days over 2000m with my P3S and Argtek antenna system.
I decided to put together two windsurfers I had doing nothing into one tall unit to place behind the 5.8Ghz Argtek antenna ............... 4800m !!

Nuff said I think !!

Nigel

 

[dchao]

If 'dchao' was right - which we know he isn't ... it would mean that we can throw away all our Satelite TV dishes ...

solenlife, I really do not care what you think. Go study how a parabolic antenna works before you come back.
If you have a look at your sat dish, the feed antenna is facing away from the source and aiming at the dish, it's not omni-directional like your RC antennas. Maybe if you've made your windsurfer like a sat dish, that would work better.
I still standby my original opinion, the direct signal which the antenna receives is a lot stronger than reflected ones, and the reflected signal are most likely to be very weak or out-of-phase "noise" which are useless. The reflector is more for blocking unwanted signal than as a reflector.
If the "parabolic" reflector is so effective, can you tell me why a old CD can also be used as a windsurfer and just as effective? And why doesn't your windsurfer require a precision aiming just like a sat dish?
I have found my windsurfer to be totally useless in a rural area, but quite useful if there is a lot WiFi in an urban setting. YMMV.

 

[N017RW]

Actually, any reflector will
improve signal so please post your data to support that a CD, etc., is JUST AS effective as a parabola.
Your dish point has merit but is not mutually exclusive with the cylindrical parab./dipole combo.
There are technical reasons why a tv dish requires precision because of the LNA/LNB design, signal polarity, aperture, etc.

I appreciate skepticism but not claims without data or reviewable materials.

Link: index

 

[Paul Sw]

The reason a satellite TV antenna needs to be accurately pointed is the much narrower beamwidth. K-band with a wavelength about 2 cm is often used for satellite TV. Referring to my post #24, the beamwidth for a 40 cm diameter TV reflector operating at 15 GHz is 60 x 2cm/40 cm = 3 degrees. This can be compared to the approximate 90 degree beamwidth of a windsurfer.

Paul