Is it possible to create a digital link over a kilometer in length using the nordic parts available here? One-way link is ok, bidirectional is preferred. Communication speed of 2Kbps should be enough, 4 Kbps preferred.
I think the answer is no, but wanted to be sure I did not miss something
with highly directional antennas, I bet you could do it. I know that off the shelf wifi routers with high-gain/directional antennas have been made to do 20 miles or more.
one of the nodes (the transmitter) will be moving over 100 mph. No directional antennas 
100% clear line of sight? If yes, you can do the math and find out, for various choices of antennas.
It is doable, with $$$$ for antennas and starting with 50-100mW transmitters.
If non-line of sight: no.
Speed is not an issue low bit rates.
I’ve obtained almost a mile with a pair of 802.15.4 XBee modules, 60mW each, one end iwth 5.6dBi omni, the other with a zero gain PCB antenna. If one end had, say, a 14dBi antenna, a mile would work. If both ends had this much gain, well, you see. Key though is the right kind of bandwidth and modulation. Lower speed, lower bandwidth is always better. 802.15.4 uses O-QPSK which is very tolerant of multipath. Doppler from speed isn’t an issue at the chip rates in '15.4.
YOu can do a link budget spreadsheet easily enough and do what-if with antennas, path loss versus distance, etc.
dmitrygr:
one of the nodes (the transmitter) will be moving over 100 mph. No directional antennas
nothing like putting all the data in the original post. any other “minor” issues you haven’t mentioned?
sorry. Yes, always line of sight. Xbee modules ara available here in those power levels?
dmitrygr:
sorry. Yes, always line of sight. Xbee modules ara available here in those power levels?
where’s “here” ?
The radiated power is mostly from your choice of antenna not the radio itself, though the XBee PRO at 50mW is a good start. If legal in your country. The regulations likely limit the radiated power. In the US, the rules say you can radiate higher power with more directional antennas; there’s a formula.
This should be trivial!
Simply build a tracking radar that controls a gyrostabilized platform that can always keep a high gain antenna pointing at the receiver as the transmitter moves and there you go!
Guy I work with built one of these for military aircraft 20 years ago: it’s a solved problem. :twisted:
In order to boost the performance, you could consider a 2.4GHz power amplifier.
Here is a link to one manufactured by SST. http://www.semiconductorstore.com/cart/ … oduct=9404
Might not get you 1km, but it will definitely increase performance.
Good luck.
-Brian