DIY Patch Antenna

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tfish

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This is not a build thread, although I am making a couple of these.

There are a couple of sites that show you how to build simple patch antennas. You need to do some simple math to figure of the size of things for 900mhz.

I think the first one has already been posted in one of the Eggfinder threads and maybe even on his webpage.
https://www.rc-cam.com/gp_patch.htm
and
https://www.rcgroups.com/forums/showthread.php?t=1292451

In one of the threads they use some 26 gauge Galvanized sheeting , Homedepot Lowes etc. I bought the 26 Gauge and it's pretty flimsy. I'd try to find something thicker. 26 gauge might work well for the size of antennas they are making. When you scale them up to handle 900 MHz they get pretty big, and flimsy out of 26 gauge. Using either of these sites to build a patch antenna will make your antenna about 8-10 inches in size.

The other thing to research are the SMA connector or connectors need to get it from the antenna into the EggFinder LCD. It made me go nuts trying to figure out what to order. I ended up going with a SMA Female RIGHT Angle Solder PCB Mount RF Connectors for the antenna. And a SMA Female to RP-SMA Male RIGHT Angle RF Connector Adapter to adapt to the EggFinder LCD. Joint the 2 with a short cable I had. I've not received all the parts yet and I may still be going crazy.

Just a heads up.

Tony
 
Thanks for the link. I have thought about building a patch antenna but have never gotten around to it. I like the fact that it can be built with no coax cable to keep the system noise figure low.

In one of the threads they use some 26 gauge Galvanized sheeting

Tony

This seems like a very poor choice of material for any antenna. Copper would be a much better though expensive choice. Brass would be a second choice, not as good as copper but better than steel.
 
Looks like the ground plane would need to be a little over 11.15" square on a side. If going without using coax cable, would need to build a little tray/support for the EF or LCD receiver as I don't expect the connector would be able to carry the load. But boy oh boy I bet the additional reception range would be considerable. Since I've read were a person achieved 18k' with a decent duck antenna, this could stretch it further. Kurt
 
For specialized or hard-to-find connectors and connectors with coax, I recommend Pasternack -
https://www.pasternack.com/
They are NOT cheap, but they are very good. I've used them in several research projects needing RF connector assemblies.
 
We ran a two pairs of patches at Balls this year.
Pairs set to add together for gain and two different frequencies - work very well!
 
The beamwidth on 900Mhz is wide enough for in flight tracking of the NMEA trackers with the patch antenna. A 900Mhz Yagi technically has a much narrower beamwidth which makes in flight aiming more difficult. That said, once the rocket is down and generally in a fixed position (as long as the wind isn't blowing it all over the place) the Yagi can increase the ground footprint because it's easier to aim at the generally fixed target transmitter.

Now on the 70cm (420 - 450Mhz) band, 1.25 meter (219 - 225mhz) band and 2 meter (144 - 148Mhz) band, the beamwidth of a Yagi is sufficiently wide enough to be used for in-flight rocket tracking hence you see people using them there. A 3 element Yagi on 2 meters has pretty long elements but it's
doable. 1.25 meter the elements are shorter and on 70cm the elements are shorter still making a 7 element Yagi workable there though 5 elements is
generally sufficient.

For sport flying just to be able to find the rocket, stock antennas are sufficient. If one is a "live data" fanatic, anything to increase the receiving gain or power output will increase the chances of successful decoding of the NMEA sentences coming off the tracker. Why you can't get every single position received would take a long discourse to explain but in reality all it takes is one successful position report just before the rocket touches down and you'll get it back. Hence the reports of folks successfully finding fincans sticking out of the ground on totally sight unseen ballistic flights. If the position is received before the rocket hits, proceed to that point and the rocket (remains) will likely be in that general area. Kurt
 
The beamwidth on 900Mhz is wide enough for in flight tracking of the NMEA trackers with the patch antenna.
I thought I would be clever and point the 435MHz version up (slightly off vertical) and the rocket would just fly into the more sensitive part of the beam pattern as it ascended. I was expecting enough signal when the rocket was on the pad for the link but I ended up being very disapointed and surprised. Link was not working on the ground with that antenna attitude.

Now I just use an omni-directional antenna for the lower flights if I do use the patch I track the rocket position manually. It's easy to do when using a tripod.
 
Yea - the receive pattern sucks at the horizon.
We use them to track & record the FLIGHT phase unattended.
More directional antennas are used during recovery.
No antennas are needed to find the pad. ;-)
 
I've mounted my patch on a 10 foot pole: https://www.rocketryforum.com/threads/missile-works-rtx.126340/page-11#post-1615206. Scroll down and you'll see the picture. I have no trouble on the horizon reception. Just lower it backwards to track the rocket up. Even if you can't see the descent, you can eyeball the position by referring to the altitude and distance on the LCD screen and point the patch accordingly. Get a nice report at the last known position and ditch "the patch on a pole" and use a stock omni or a Yagi for the recovery. Kurt
 
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