Antenna Alternatives
Antennas now has its own section in the Forums
There are alternative antenna choices for your UAV when space is a consideration. RHCP antennas are without doubt one of the best choices you can make for your video and telemetry signals. I had wanted to use a RHCP antenna for telemetry for my X-8 but the choices I had come across were pretty space demanding. Surfing the web doing some antenna research I ran across these wheel antennas from Kent Britain WA5VJB, a fellow amateur radio operator. www.wa5vjb.com He's got some really useful designs other than the wheel.
I purchased 2 of the 900 mhz variety for the telemetry, one for in the X8 and one for the ground station . Since the plan is to install all antennas within the X8 these are a great space saving choice over the current offering of cloverleaf antennas. The 900 mhz wheels measure about 4.5 inches in diameter, somewhat smaller than a CD ROM and only slightly thicker. The best part being they are only $ 12.00 each. They can be fed with coax directly or as seen in the photograph you can solder a circuit board SMA connector of your choice to the center in the holes provided.
These wheel antennas are considered to be horizontally polarized at the plane of the horizon however as your UAV gains altitude the wheel antenna emits a cross polarized signal. Here is a quote from hamtv.com “Around 1990 the first launch of a balloon borne payload in the Denver, Colorado Area took place sporting a Little Wheel as the radiator for the on-board ATV transmitter. It was found to work quite well and had some interesting attributes that were previously undisclosed. Those being that the Wheel antenna although being a horizontal radiator on the horizon displayed properties of cross polarization above and below the array - similar to two in phase horizontal dipoles. This worked to the advantage of the ground station by employing a circularly polarized antenna (Helix) - also a fixed horizontal antenna directly below at the launch site would not see the up to -30 dB nulls as the balloon rotated. The horizontally polarized tracking antennas (Yagis) were receiving a signal of constantly changing polarity as the payload rose to an altitude at which it would start to drift away from the launch site and the horizontally polarized tracking antennas would become more effective due to the horizontal polarization emitted from the sides of the Wheel. The pattern of the Wheel is within +/-0.5dB of being a perfect circle in the E-plane. In the H-plane the pattern is +/-35 degrees of the horizontal axis of the antenna. These figures equate to ~ 4.28 dBic gain or 6.38 dBdc. The dBic gain above and below the array is somewhat indeterminable due to the fact that the circular polarization exhibited is quasi-circular or cross polarized; however, it responds to a Helix in a manner consistent with the gain of a pair of like sense Helices in a system looking at one another. ”
This antenna does radiate well (60% efficient) and also radiates well in the second and third harmonics so take precautions to provide filtering for your transmitter.
You’ll want to use a “Wheel” antenna on each side of your link as losses will result if mated to just a dipole when your UAV is overhead. Just mount it in a horizontal position at each end of the link. If it fits inside your UAV that’s great but it could also be mounted flat on the wing as well.
Holes are provided for SMA circuit board jack mount
or direct connection to coax.
This link shows the antenna being tested in a 3D pattern.
http://www.youtube.com/watch?v=vVW9jZG1vI0&feature=player_detai...
i'll post my actual installation once I get there.
Keep experimenting with radio, get your tech license, it's easy and you'll be contributing not only to this great hobby but ham radio as well.
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Comment by Kevin Brown on October 6, 2012 at 6:02pm -
Very Cool antennas, Thanks for the source you would thing you could get something like this in the US
KI4SCC
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Comment by Flying Monkey on October 6, 2012 at 7:45pm -
That's pretty neat! Too bad they don't have that one in 5800 or 2400... :(
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Comment by Geoffrey Preston on October 6, 2012 at 7:55pm -
He has a wheel antenna for 2400 mhz, I think it's only $6.00, so $12.00 for the set
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Comment by Flying Monkey on October 6, 2012 at 9:35pm
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Oh, guess I didn't look close enough... I might try that 5800 patch, but I still wish there were more options out there for 5.8ghz. Anyways, nice find!!
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Comment by Brent on October 6, 2012 at 10:25pm -
I like L-com Antennas and Amplifiers. Lots of antennas to choose from including LHCP and RHCP in 900, 2.4 and 5.8 bands. Reasonably priced and great technical help and returns. Used them for 11 years and the original equipment is still operational.
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Comment by Veikko Vierola on October 7, 2012 at 3:05am -
That is very cool, got anything for 433MHz?
BTW, how do you get the antenna sending only with part B or is the antenna sending with the full length (A+B) of the copper cord on the PCB?
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Comment by peppe on October 7, 2012 at 5:20am -
hi guys
the best "match" is using a vertical bent-dipole (on board) and an helix axial-mode (on ground)
for short distance, a circular-pol patch or a quadrihelix is allowable @ ground station
Big Wheel is essentially a horizontal pol, omnidirectional antenna. Poor antenna
no circular components because no delay lines between arms.
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Comment by Geoffrey Preston on October 7, 2012 at 7:15am
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@ Veikko Vierola
Here is a photo that thru transparency shows the trace on the reverse side of the board. It is
3 full wave sections.
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Comment by Geoffrey Preston on October 7, 2012 at 7:35am
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@ peppe
If the elements were half wave there would need to be 180 degree phasing lines between the elements to get circular polarization. However these are full wavelength elements and this antenna is a more 2 dimensional representation of the cloverleaf or skew planar wheel which are circularly polarized either right or left depending on the direction of the winding (current). If I had a choice between polarization of strictly dipoles I would choose horizontal over verticle on crowded bands where most everything is transmitted vertically, the 30 db inherent loss over difference in polarization would be of great benefit. This is why it is important to use like antennas. Receiving a vertically polarized signal with a helix versus receiving it with another helix results in loss of signal strength.
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Comment by peppe on October 7, 2012 at 8:11am
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@ geoffrey
tnx Geoffrey for replying, but I disagree.
180 degrees is the same polarization.... we are talking about vectors 2 dipoles at 90° must to be feed with 90°delay (phisical, electric or a summa of both).... in the 3 elements of wheel I cannot see any delay, so, no plane of vectors change, and no circular pol.
we are speaking of airplanes, so, very different attitude. The best antenna is isotropic antenna, but..... it doesn't exist.... the only way to get closer is a bent-dipole, that is a little worse than a dipole, but no "holes"....(almost)
loss between hor and vert pol 18dB
loss between LH and RH circ pol 30dB
loss between linear pol. and circ. pol. 3dB (signals always present)
I don't like cloverleaf or skew planar (they are not circular polarized, they just have some vectors in different planes, it's not the same)
finally, the best couple is bent-dipole+helix (or circular patch), that is what is used in aeronautical, military and space applications.....
I'm sorry for my poor english..... I hope to talk about more and better
Peppe
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