Communication range testing.
Well, communication protocol done. Now core BT module (cubesat/lunar modem) is capable to work in modes:
(a) 3 frequencies listening; 3 frequencies for transmit; 2 from 3 majority bits correction, bits shifting correction fix for preamble lost; synchronization of a frequency switch; lost switch frequency correction; adjust frequency on temperature drift.
(b) 1 frequency listening; 1 transmitting; the same functionality as on (a) but switching is disabled.
(c) 1 frequency listening; 3 transmitting; again same functionality; that will be main mode for a cubesat and lunar probe.
(d) 3 frequency listening; 1 transmitting; difference from (a) that it will be 3 receivers monitoring 3 frequency but transmitting goes over 1 frequency. That mode will be on ground station – to maximize probability for cubesat/lunar probe to get less noisy data;
In mode (d) instead of processing and fixing packets inside micro processor data will be tunneled to a PC and fix of data can be done locally on a more powerful desktop, or distributed to network of a computers for simultaneously error correction (for such process can be used screen savers with instant win notification for a Team Plan B supporters).
Mode (c) allow to have transfer data from cubesat/lunar probe without delay for frequency switch synchronization. That can increase data transfer from 50 kbit/sec to 70-80. Transfer date for upload is not critical. Another reserve is tweaking core module from 250kbs to 1mbs – that can give increase of a speed up to 160kbs for download data from cubesat/lunar probe, for sure such increase will require more computer power after ground station processing, and will make a sense only with good network of a “fixing” packets screen savers.
Why to invent a communication protocol? Usually 99% of a time of software development spend (lost) on following standards. Needs to do something fast == ignore standards and write from scratch (see code at http://www.adobri.com/misc/STM_BT/STM_BTCM.c).
Range test, two helical antennas, one for Cubesat prototype 3 turns http://www.shapeways.com/model/322768/small_2_4ghz_antena__for_cubesat_.html?gid=sg85851, another for a ground station with 1/3 of a turns on 3D printed antenna http://www.shapeways.com/model/322767/2-4ghz-antena.html/?material=6, transmitting power 1mWt, LNA 12dB. Normally that is a Bluetooth with a range of 10m. Testing on 25m == OK, testing on 100m == OK, but it shows that best reception will be with antennas pointing 10-15 degrees up instead of direct pointing (do not judge seriously = truly speaking designers was zero experience in antenna’s design), test over water at False Creek at Vancouver did not show good reception – looks like ground or water disturb signal, lifting tripod with transmitter and receiver manually just 1m up improve communication. Problem was corrected on a 5 block near Queen Elisabeth Park – road is strait, not much cars, hills from both side == manual holding and pointing allows to confirm communication over 450m.
That actually brings limits of a test for a ground station, the best place will be a Squamish Chief == face of cliff is around 700m and ground station has to be pointed with 45-60 degree to horizon.
Next step – amplifiers to increase power transmitting to 1Wt (in Canada allowed 4Wt), and mobile ground station assembly/functionality.