Finding Models with an Omnidirectional Antenna

Losing models is a pain, and the smaller they are, the easier they are to lose.

There are expensive devices that will detect which direction your craft is in, but even if they were cheaper, tiny models can't carry such things.

Here's a video I took earlier today when my Nano QX FPV went down in a field and I needed to get it back.

The technique centers around the fact that "omnidirectional" antennae aren't truly omnidirectional. The cloverleaf and dipole antennae that most people use for FPV can't sense anything directly above or below them, as seen in this diagram:

As you can see, the sensitivity of the antenna (indicated by the distance of the blue line from the center) is greatest out to the sides and drops to basically nothing along the axis of the antenna.

Knowing that this is the case, we can point the axis of the antenna out toward where the model might be and sweep it back and forth, watching the video feed as we do so. When the null is pointed at the model, the video will break up, as seen in this silly cartoon:

This will give you an idea of which direction your model is in so you can get closer. As you're moving in the direction indicated, sweep a few more times so you don't accientally go too far.

You can also use a similar technique with a radio that provides telemetry, such as the FrSky Taranis. Point the radio's antenna out where you think the model might be and sweep in the same way, watching the RSSI for a dip.

Remember, the cone of null signal is very narrow, so you may have to move it up and down some as well as side to side.

I hope this article helps some of you recover craft that would otherwise stay lost. Happy flying!