Antennamania

As promised in my last post, here is a small write up on my long night of antenna building last night. Partly inspired by a perceived need to boost our FPV range and partly inspired by an ever-growing list of things I really didn't want to do, I decided to build some antennas. This was my first foray into antenna building and it all still seems to be black magic to me, so I stuck with the very well put together tutorials by IBCrazy (Alex Greve, pretty much the undisputed leader in FPV antenna development). Over the past few weeks and months I have thought a lot about antennas and what we want out of ours, so when I decided to build some, I had a decent idea of what I wanted. I wanted to make a highly directional 1.3 GHz FPV antenna for our receiver, a 1.3 GHz FPV transmitter antenna with good long range strength, and a more directional antenna for our UHF (433 MHz) RC transmitter. Below are my antenna choices.

For the directional receiver antenna I decided on the biquad. To me it was appealing because it is simple, elegant, fairly easy to build, and has 11 dBi gain (effectively doubling the range of the 8 dBic patch antenna). Below is a picture of the antenna; find the link to IBCrazy's tutorial a the bottom.

1.3 GHz Biquad antenna. 11 dBi gain. Using RG58 coax, 10 ga solid copper wire, and steel sheet.

For the video transmitter antenna I decided on a simple half wave dipole. My reasons were simple, the antenna has a toroidal radiation pattern which puts its radiation out in a 360 degree beam but not vertically up or down (which would be wasted energy for us). It is also exceedingly simple to build.

1.3 GHz half wave dipole. 2.15 dBi gain. Using RG-316 coax, 18 ga stranded wire, and a protoboard.

For the UHF transmitter antenna I decided on a Moxon. This is basically a Yagi with no parasitic elements (only a driven element and a reflector). It is ideal because it is, again, pretty easy to build and significantly more directional than the stock antenna. It has a gain of 5.75 dBi. This one is still a work in progress, as I decided to prioritize the FPV antennas. I'll get picture of it up here as soon as its done.

When it was all said and done, this is what the plane looked like. The GoPro is mounted using 2 velcro straps passed through holes cut in the FPV plate. The dipole was mounted on the left side of the nose (right from this point of view) just below the GoPro.

The transmitter and battery were mounted to the bottom of the FPV panel using velcro. This made for a very compact package which can be readily removed from the aircraft.

Video transmitter antenna tutorial (includes 2 types of half wave dipole and the inverted vee)
Biquad video receiver antenna tutorial
Moxon antenna tutorial (includes 3 and 4 element Yagis as well)

UPDATE: The BiQuad is an amazing antenna. It, along with an RMRC 1.3 GHz rx, RMRC 800mW 1.3 GHz tx, vertical half-wave dipole, high pass filter on the rx, and low pass filter on the tx gave us 12.8 km of absolutely rock-solid video. We were flying in clear conditions 250 m AGL with the rx antenna 2 m AGL. We lost Dragonlink 433 MHz connection and were forced to turn around before getting so much as a hint of degradation on the video.