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significantly more range. There are two basic types of commonly used directional antennas for
rocketry applications, the panel antenna and the Yagi. A panel antenna is basically two
conductive sheets of a certain size, separated by a space; the forward-facing panel is connected
to the antenna signal lead, and the opposite panel (which is usually a little bit larger) is
connected to ground. They are relatively easy and cheap to make, and the gain and
directionality can be controlled by varying the sizes of the panels. They typically have a
beamwidth of 30° to 120°, depending on the gain and bandwidth (how sharply the antenna is
tuned to your specific frequency). A Yagi antenna looks like a stick with perpendicular
“sticks” coming out of it, they are a high-gain antenna but tend to be very directional. Yagis
are very popular for beacon type rocket finders, because you need to find out as closely as
possible where the source of the signal is.
In our case, you want the antenna on the transmitter to be an omnidirectional antenna, since the
signal needs to propagate in all directions because the rocket is moving so the radio signal may
be moving around in relation to the antenna. An omnidirectional antenna ensures that you will
get a good signal regardless of the orientation of the rocket (unless it’s directly overhead).
Therefore, there’s not much point in messing with the antenna that comes with the TX board,
unless you have to use an external antenna (for example, because you have a carbon fiber
rocket). In that case, you will want to get an omnidirectional antenna with a RP-SMA
“pigtail”, so it can be connected directly to the RP-SMA connector on the TX board.
You can also use a “rubber duckie” type antenna that screws directly onto the RP-SMA
connector on the Eggfinder TX board. Some of these antennas will improve your transmit
range, but be careful when you look at the specs; if the gain is over 5 dB, chances are that the
beamwidth is narrower too, so you may have trouble picking up the signal as the rocket gets
close to you, even though it’s technically stronger.
The receiver antenna is where you’re going to be able to make the most range improvement.
Using a higher-gain directional antenna, it’s possible to get twice the range of the standard
stick antenna, at the cost of having to point the receiver’s antenna in the general direction of
the rocket. A panel antenna is ideal for this purpose, because it has a good balance of gain and
beamwidth; you don’t want the bandwidth to be much less than about 60°, or you may have
trouble getting a signal if your rocket goes out of sight and you don’t know which way it went.
We’ve used commercial panel antennas such as this one made by Arc Wireless:
http://www.streakwave.com/mmSWAVE1/Video/ARC-PA0910B01.pdf
This particular model has 10dB gain with a 60° beamwidth, which is ideal for picking up the
Eggfinder RX’s signal from out-of-sight rockets. It costs under $20. You can also make your
own panel antenna, there are some good references out there on the Internet, such as
http://www.rc-cam.com/gp_patch.htm
which shows you how to make a patch antenna for under $5.
With any external antenna, you will need some kind of cable between the antenna and your
Eggfinder RX board. You may need to put some kind of connector on the antenna side of the
cable, particularly for a commercial antenna; for example, in the case of the Arc Wireless panel
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