FPV ray gun

by Tinfoil_Haberdashery | April 22, 2014 | (17) Posted in Projects

Hello everyone. Though it's not quite done yet, I wanted to share my most recent project: A 900mhz FPV groundstation.

I wanted to build a long-range antenna for my 900mhz FPV system. I was very inspired by David Windestål's "overkill" FPV groundstation, but didn't have any G10 fiberglass or a CNC machine. What I did have was oak, so I decided to go with a slightly different aesthetic--an aesthetic that says "I'm Captain Nemo in a cowboy hat".

Almost all the wood used for this build is 1/4" oak, milled from a tree that fell on a friend's property. The handles are made from some oak chair legs I found at Home Depot. It's held together pretty much entirely with 2-part epoxy. I designed the grip to emulate that of a chainsaw, which is also a heavy tool of a similar shape that must also be wielded with extreme precision.

I built the antenna using I.B. Crazy's guide. The helix is 3/16" copper tubing and the reflector plate is made of aluminum with copper foil laminated to both sides. I could've used a solid copper plate, but this would've been heavier and much more expensive. I had originally intended to use bare aluminum, but found that impossible to solder, so I decided to laminate it with copper for practical and aesthetic purposes.

The copper pipe endoskeleton not only provides handles with which a spotter can aim the antenna, it also protrudes from the bottom to form a support. This serves two purposes: It keeps the weight of the unit from resting on the delicate reflector plate, and it cants the antenna up at an angle so it can be used just sitting on the ground.

Yes, it's a jumble in there. I'll try to hit all the major points of what's going on; I've got two 900mhz receivers, one hooked up the the helical antenna and the other to a SMA female port on the top of the box (currently outfitted with an omnidirectional CP antenna). The red circuit board is a Range Video diversity controller. At the back, you can see a gold panel mount plug; this is a stereo plug I've wired up to send power and signal to my screen or goggles via just one 3.5mm stereo cable. It's also got 10 amber LEDs which were originally supposed to function as a power meter but ended up simply as an indicator lamp when it became clear that my knowledge of circuitry wasn't up to the task.

The side panel is held on with magnets that secure to the 4 steel tabs at each corner of the enclosure.

Here's a shot of the rising sun ornament with the LEDs lit. Also seen is the newly-installed knife switch, which isn't in the other images.

This is a close-up of the antenna connection and impedance matching solution. I did an impressively awful job soldering it, but for all that, it works phenomenally. The range and penetration is vastly greater than what I was getting with the omnidirectional antenna.

Finally, I wanted the unit to be fully tripod-mountable, so underneath the plate for the receivers there's a T-nut threaded to accept standard tripod mounts. The thing weighs 7 lbs. (3 kilos) and it's a little ungainly, but it works.

And when I'm not using it for flying, it's a great costume piece!

COMMENTS

Hasersys on May 9, 2014
Just curious, hopefully I didn't miss it some where but what made you go with more turns in the antena? Is that do to the diversity you are running. I could have this all wrong but, the more turns the more narrow the band is? The less the wider the band? I have one similar to your build but on 1.2 or 1080 to be exact, I will have to look into doing the diversity like you have I like your build it is amazing, and looks super cool.
Log In to reply
Tinfoil_Haberdashery on May 9, 2014
Yeah, the more turns, the narrower the beamwidth. In this case (as near as I can calculate based on Wikipedia) we're looking at a half-power beam width of 127 degrees or so. This means (I think) that your signal strength will drop by between the dead center of the helix and 127 degrees off that mark in any direction. David Windestål's groundstation (with 3 turns) has a half-power beam width of 180 degrees.

If I'm honest, the number of turns I picked was pretty arbitrary. I wanted as long a range as I could get while still having the station be a manageable size, AND have something with aesthetically pleasing proportions. 6 turns was the result.

The narrower beam does get you an increase in range. According to the best data I can find and Alf's Max Range Estimator spreadsheet, my antenna gets about 150% the range it would if it had three turns.


Log In to reply
Hasersys on May 10, 2014
Well you have succeeded! Your antennas aesthetics are unbelievably pleasing. I am very interested in your antenna. I hope you keep us updated, and I hope i do not miss the post!
Log In to reply
MT Alex on May 10, 2014
Well done, I really like the way it turned out, very steam punkish.
Log In to reply
Jeffry Rice on May 10, 2014
very steampunk!
Log In to reply
Zatoichi on May 10, 2014
Dude Well Done! It is a very creative piece o kit. Thumbs way up.=D
Log In to reply
Zatoichi on May 10, 2014
I want to see it in action!
Log In to reply
ztoon on May 13, 2014
me too...a little youtube video?
very nice work.
Log In to reply
stephen on May 11, 2014
Awsome steam punk. Great job and looks the part
Log In to reply
galaxy engineer on May 18, 2014
I love the departure from the normal look! This is a utilitarian look of the turn of the century. I agree wholly with Steam Punk comments. I have built a couple of what I thought were cool looking ground stations and wrote some articles on them but I am jealous of this one and humbly bow to the master! Very well done!
Log In to reply
Jeffry Rice on May 10, 2014
last pic made Lolz, keep it up!

Log In to reply
N8rox on June 8, 2014
nice job

Log In to reply

You need to log-in to comment on articles.


FPV ray gun