Eggtimer Rocketry Eggtimer TRS Assembly Manual page 37

Eggtimer TRS Antenna Options
The Eggtimer TRS has pads for either a permanent "stick" antenna or a RP-SMA edge
connector for a removable/remote antenna. Your choice of antenna will depend largely on
your rocket, how you plan to mount it, and how much range you need.
The standard Eggtimer TRS ¼ wave "stick" antenna is very simple and produces decent gain
without being directional (i.e., the signal strength is pretty much the same in all directions).
We have maintained a line-of-sight range of over 8,000' with this antenna, we think that most
people will find that this simple antenna will suit their needs just fine if your primary goal is to
get good enough GPS data to help you easily find your rocket. It's relatively small, very
lightweight, and easy to build.
In some cases, however, you may need to use a different antenna, or a remote antenna (for
example, if you have a carbon fiber rocket; you can't mount an antenna inside a CF rocket
because they block RF signals). You will also need to use an external antenna if you are
planning to mount the Eggtimer TRS in a AV bay with allthreads. If you want to track your
rocket's flight as accurately as possible or if you are intending to fly over 10,000', you may
need to use a higher gain antenna, such as a 5 dB dipole antenna. In that case, you will want to
go with the RP-SMA connector option.
Note that any antenna that you get must have an RP-SMA MALE connector on it; this
connector has INSIDE threads with a JACK in the center of the connector. It must also be rated
for the 900 MHZ band, NOT 2.4 GHz. Be careful what you buy, we have seen some eBay-
type vendors that are selling 2.4 GHz "WiFi" antennas for use with 900 MHz systems. They
"will" work, but they are certainly not optimal, and would most likely produce less range than
the stick antenna. Also, be sure that it's a RP-SMA antenna; we've seen some vendors selling
standard SMA antennas but calling them RP-SMA. Finally, we recommend that you don't buy
an antenna unless the vendor has the data sheets for it, showing the SWR and the beam pattern.
An optimal SWR for a 900 MHz band antenna would have a center frequency of about 915
MHz, with a SWR in the low 1's at that frequency. If the graph doesn't look like that, it's
probably a wideband antenna and you need to look elsewhere.
Note: You MUST use an "omnidirectional" antenna on the Eggtimer TRS board. The gain on
the antenna must be 6 dB or less. Do NOT use a "directional" antenna; they only work in one
direction, so if your rocket isn't pointing in your direction you're not going to be able to pick
up a signal.
Typical antennas that you might use are the Linx Technologies ANT-916-CW-QW or ANT-
916-CW-HWR-RPS, they're about $10 from major electronic distributors. The first one is a ¼
wave antenna, the second is a ½ wave antenna, which is a bit longer but will give you higher
gain.
Directions for installing a RP-SMA connector are at the end of this manual; the following
instructions are for the "stick" antenna, and can be skipped if you are going to use a connector.