The radio is basically a Morse code FM transmitter. The low data rate of Morse code demands only 10% of the satellite’s power budget to reach a ham radio on earth.
The dipole antenna design was chosen for its simplicity and its non-direction-selective radiation pattern.
Requirements:
- Signal strength sufficient for reception by typical ham radio on earth
- Less than 20% consumption of total available power
- Receptivity independent of spacecraft orientation
- Transmitting in license-able band
Specifications:
- 100 mW BeeLine EIRP FM transmitter
- Transmitting at 435 MHz, in the Amateur Radio Satellite Service Primary World-Wide Band
- Dipole Antenna has 1.7 dB of gain with omnidirectional radiation pattern
- 13 cm length for each antenna pole (=1/4 transmitting wavelength)
The primary ground station for EquiSat will consist of a receiving antenna and recorder device located at Brown University. This ground station is in development and will be able to continuously monitor EquiSat’s transmissions when the satellite is in range.
Meanwhile, EquiSat is designed so that ham radio operators will also be able to receive signals. This will be tested and accomplished using the Arrowhead Arrow II Antenna connected to the FUNCube Dongle. This combination of receiver antenna and driver/software has been successfully used by ITUPSat, which is currently flying the same BeeLine radio transmitter that EquiSat is using. It is important to note that any ham radio receiver-antenna setup will be able to receive transmissions if it is tuned correctly.
Because the antenna’s two poles must be longer than the side length of the cube (13 cm vs. 10 cm), the antenna is launched coiled on the top of the satellite and tied down with nylon fishing line. The fishing line is intersected by a thin piece of nichrome heating element that is heated electrically once in space to melt the nylon and deploy the antenna. The antenna is made from highly elastic nickel-titanium, so it easily springs into position when released, much like measuring tape.
Here is diagram showing how the nylon fishing line will be cut by the nichrome heating elements, releasing the antenna, and the fastener that will be used to mount the antenna to the satellite.
Antenna Fastener: The dipole antenna leads will go through the fastener, and the antenna ends will be secured but the fastener’s top edges.
Dipole Antenna: Leads on right connected to coaxial cable, nitinol antennae on left
Coming Soon…
