When I heard about a 1.3m prime focus dish offered for 40€ at a garage sale I couldn't help myself but buy it.
Since I played with the thought of receiving NOAA images on 1.7GHz this antenna seems to fit for that project, although it could be wider. At operation frequency the wavelength is about 180mm which could result in 25dBi gain (which is way better than a quiet long 22 element yagi-uda at about 15dBi). All values are calculated and so will vary in reality.
Stages for this project are:
1 - build rotor
2 - build controller unit (raspberry pi with rtl_tcp server for radio data, rotctld server, motor controller)
3 - build antenna (biquad antenna with an optional amplifier)
4 - testing
Right now I am building the azimuth/elevation rotator rack.
Right now this log only serves as a collection of ideas, here's what I plan as second step:
To control the hardware part, the next step is to build a controller unit.
It will hold a raspberry pi, a RTL-SDR stick, motor driver and software to glue all three together.
RF decoding will be done by a RTL-SDR Stick, radio data will be streamed by a rtl_tcp server running on the pi.
What I want is the controller to accept commands from the hamlib rotctl client. Therefore I'll be writing a python script listening to incoming tcp connections, rotctl_server.py (which will be avilable sometimes later under the file section of this project). This script then will call out via serial terminal to a controller-board (some arduino or PIC controller) which subsequently talks to some A4988 boards. I recently had the fortune working with these A4988's for another project and I like them, so they will be my first choice. They are able to deliver a decent current to stepper motors and allow for microstepping. And they are cheap. The dedicated driver board will support emergency-stop-, position- and end-switches for safety reasons. I don't want to damage the device, me or someone else because I made a mistake in programming.
Currently I'm fiddeling with Mark 3 of the rotor hardware.
At first I tried to drive elevation with a pulley which is way to wobbly so I scrapped it before even trying it out. I( will never use pulleys again if sub degree precision is needed.)
My second approach to elevation control was with a linear motor from a hospital bed. It looks promising.
It was then when I realized that it is a bad idea to rotate everything on a big wooden wheel on cheap wheels for azimuth control (this can be seen on the first image in the gallery) so right now I'm building the third Mark.
It will have a fixed bottom frame, azimuth rotation around a low friction ball bearing and elevation is rotated around another set of ball bearings mounted in a new steel frame.
This is a sketch for Mark 3, most of these parts are ready for assembly.
Once again, more photos will follow soon.
A minor update:
I tried to 3D print gears for el/az control. This turned out very bad, maybe because my 3D printing skills are too low or this process is just not right for this high torque, low speed, high accuracy application.
So.. now I'll order some solid metal gears (pun intended).