[time-nuts] Toy radiolocation and LORAN envelope
jleikhim at leikhim.com
Tue May 27 12:45:25 EDT 2014
I built some RF beacons for my friend's high power (TRIPOLI) rocketry
projects. We use a TELEVILT UHF wildlife tracking receiver from Sweden
(pricey) that operates in the 434 MHz ISM band. The transmitters are
LINX TXM-LR series transmitter chips with an 8 pin PICAXE processor. The
modulation is OOK (pulsed CW) for best signal to noise using the
TELEVILT narrow band receiver and its BFO.I will share some code
examples if interested. It was pretty simple. The FCC part 15 rules
unfortunately are restrictive on duty cycle so you need a ham license to
operate them. If I had gotten fancy and made them transpond upon
interrogation, it could probably be type accepted. The battery is a 3.2V
CR-123 type and could run weeks most likely at the duty cycle of 1 pps.
A smaller battery is certainly possible.
If I had to do it again, I would leverage one of the very tiny GPS
receivers that are for cellphones and simply packetize (APRS) the
location data and use an FM ISM transmitter. But I would cycle to a CW
mode periodically for the high sensitivity mode. This because, in
rocketry, the antenna is often obscured when the rocket body lands on
earth. It is quite noticeable when landing since the signal drops suddenly.
Leikhim and Associates
JLeikhim at Leikhim.com
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