When operating SAT-portable, the automatic Doppler correction of 2xFT-818 can be conveniently performed by a #RaspberryPi Zero W running #Gpredict and #Hamlib. Proven solid and reliable in DXing over the last 2 years. Read on for details 🧵

#amsat #hamradio #amateurradio #hamr
Doppler adjustment can be made manually but beyond calling CQ things get cumbersome. An automated tracking allows to quickly hop between different stations in the very limited time of the pass. For DX skeds this setup brings you spot on on the transponder frequency. 2/8 #amsat
RasPi connects to the WiFi hotspot of my iPhone enabling control and time sync. RTCZero backs up the system time. 2x CH340 USB-TTL converters connect the FT-818s to the Pi through Zero4U hub. 3/8
#amsat #hamradio #amateurradio #hamr #raspberrypi
Precise timing is crucial for overhead passes and CW. When cell coverage is absent I plug a GPS dongle into the spare port of Zero4U to feed the GPS time to NTP. The only limitation: FT-818 can't change frequency during TX 4/8
#amsat #hamradio #amateurradio #hamr #raspberrypi
RealVNC offers excellent GUI access to the Pi from iPhone. I load two instances of rigtcl deamons via shortcuts (can be loaded at startup) and from here the workflow resembles that on a desktop. 5/8
#amsat #hamradio #amateurradio #hamr #raspberrypi
RasPi Zero W has the humblest specs in the line. Yet it is capable enough to have Gpredict track 6-7 sats at a time. I work more than 7 sats and overcome the CPU limitation by utilising the module feature of Gpredict. 6/8
#amsat #hamradio #amateurradio #hamr #raspberrypi
RasPi Zero W doesn't consume much energy. A 1500mAh 9.6V battery gets me through 12-15 passes of RS-44 (without GPS). There are lighter batteries. I use an inefficient linear regulator and hence bulky heatsink for all-weather operation. The switching ones I tried were noisy 7/8
Worth to note that this was a prototype that I continue to use as is. It is bulky. It can be optimised and dolled up. The extra circuity on the lower board is for audio switching and TX breaking for Doppler control. It works but I don't use it casually. 8/8
#amsat #raspberrypi

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