Hey All,

I was just doing a bit of reading and noticed that the Goof Proof Patch (SEEN HERE) and upscaled for 900mhz ends up at just over 10" (or 263mm)

However the ones that are readily available online like these http://www.rangevideo.com/index.php?...products_id=17 are all 8.5"

Why the difference in size?? I am curious.

Cheers
-J

Originally Posted by The_Mongrel

Why the difference in size??

Subscribed. I have both antennas and I've wondered the same thing.

Cool!! I was glad it was not just me!!

The mediums between the receptor and reflector are different, thus effectively changing the velocity of propagation of the wave. Patches are a strange antenna, as they don't seem to follow the rules of the simple dipole.

The Goof proof patch uses an air medium. Commercial patches use some sort of material between the plates. I don't know what it is, though.

-Alex

Plus with the corners trimmed off it makes it circular polarized. http://www.cst.com/Content/Applications/Article/245

Originally Posted by Martin Y

Plus with the corners trimmed off it makes it circular polarized. http://www.cst.com/Content/Applications/Article/245

Well that has another completely different size again!!

The key is in a material constant called "velocity factor", usually found in the cables specs.
Simply put, the size of the antenna in open air, must be divided by the velocity factor when using other insulator between elements. But in reality is more complicated, a more scientific paper can be found here.
On the site of this guy you can buy very large band log period antennas (900-2600Mhz ! ) made on PCB, at a very low price, $12, small dimensions (12 * 13 cm), and impressive specs.
The medium of some comercial antenna is PCB too, and the size difference can be seen here, on the GP patch site. The price of commercial patches comes more from the case and cabling than the antenna itself.

PCB = Printed Circuit Board
Most PCB patches have the ground plane on one side of the board, and
the driven element on the other, so the gap is determined by the thickness
of the board which is quite small, thus all the other dimensions have to scale
down accordingly.

The difference between GP Patch and the one on the page above
is not only the dieletric (air versus styrofoam) but the spacing between elements
and total gain. The page above doesn't say what their desired gain is, but you
can see their larger air gap version has a significantly higher gain than their
styrofoam version.

ian

I want to try one of these out. I have Thomas' revision of the GP patch and it calls for 0.060" aluminum ground plane and 0.12-0.20" copper or brass for the element. I would think the ground plane thickness could be about anything, but what about the element. Thicker vs thinner? Copper vs brass? I can get 0.030 or 0.005 locally but how will these work?

After testing a commercially available patch for $60 - the performance is worth every dollar in my opinion.

Cheers
-J

Originally Posted by The_Mongrel

After testing a commercially available patch for $60 - the performance is worth every dollar in my opinion.

Cheers
-J

all commercial 900mhz antennas are linear polarization. i would prefer to buy a commercial circular polarisation antenna, but I will need to build the GP patch.

Or perhaps you sell circular 900mhz patch Mongrel ?

Hmm... I thought circular polarisation was no good for what we want.

Hmm... Maybe I am confused.

You are confused.

When two linearly polarized antennas are rotated 90 degrees from each other
they can experience a -20 to -30 dB drop in signal strength. Every 6 dB
represents a 50% reduction in effective range.

When a linearly polarized antenna transmits to a circularly polarized antenna it
experiences a constant -3dB loss but it's the same at all rotational angles.
That makes circularly polarized antennas good for tracking moving/turning targets.
You don't see more of them in use, simply because most commercially available
antennas are designed for stationary operation so they they'll just line em up
with each other and avoid the -3dB drop.

ian

Originally Posted by VRflyer

all commercial 900mhz antennas are linear polarization. i would prefer to buy a commercial circular polarisation antenna, but I will need to build the GP patch.

Or perhaps you sell circular 900mhz patch Mongrel ?

Have a look at the PDF of an CP patch I have just ordered. The company has lots of re-sellers near you. I'm paying too much for mine but it's a special order in Oz cause no-one uses them.

I'm getting this model for it's size and weight, perfect for P&T. It's not big on gain, actually only about 2-3dBi when you take into account the constant -3dBi but my intention is not long range, It's for penetration. I don't have a huge mountain to fly up, in fact my area is flat as. I like the low and fast style, so I hope this CP patch will work well when I'm below the tree line's while about 500m out.

Here's hoping anyway, will post any findings when it gets here.

Geo

I'm hoping someone has an answer to this. I set up and milled a patch out as using these dimensions
http://www.webx.dk/rc/video-wireless/PATCH4.pdf

the element is not centered on the reflector in this one but on the original gp document it is but the element is not square. is this thing supposed to be symetrical? which is correct?