PJON 3 dollars 5km range packet radio
To build a real open-source PJON packet radio able to communicate up to 5km you need only a couple (for
SIMPLEX mode) or two couples (for
HALF_DUPLEX mode) of cheap 315/433Mhz ASK/FSK transmitter / receiver modules (the total cost should be around 2/3 dollars) and the PJON library.
Please be sure of the regulations your government imposes on radio transmission over these frequencies before use.
The maximum detected range was experimented launching a balloon with a small payload containing the packet radio transmitting its position every minute. The maximum range obtained was slightly more than 5 kilometers. Two couples of STX882 and SRX882 were used as transceivers. If you choose these modules, remember to set
HIGH the pin
CS on the receiver before starting reception. Also other similar modules were tested succesfully (315/433Mhz).
OverSampling physical layer, synchronous acknowledge can reduce the maximum range, on certain media, so if you detect reduced range performance in
HALF_DUPLEX compared to a mono-directional or
SIMPLEX communication, and you can do without
ACK, configure the absence of it after the packet transmission.
HALF_DUPLEX mode have shown that it seems better to keep isolated the two antennas, using two different, not connected elements to transmit and receive. The first suggested antenna design is a wide beam pseudo half-wavelength dipole antenna made by two 345mm long conductive elements, one connected to ground and the other connected to the input or output pin.
A more directional, compact and long range antenna design is the pseudo half wavelength wip antenna. Can be easily crafted with two 345mm long insulated wire sections wrapped with each other every 5mm, one is connected to ground and the other to the input or output pin. This design helps because of its strong ground plane, often necessary to have decent results with these modules.