[time-nuts] Toy radiolocation and LORAN envelope

Joe Leikhim jleikhim at leikhim.com
Tue May 27 16:45:25 UTC 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.

Joe Leikhim

Leikhim and Associates

Communications Consultants

Oviedo, Florida

JLeikhim at Leikhim.com



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