I’ve solved my problems… Well, there are still green clouds…
Haven’t made a post in a while, thought I’d do something about that.
So I’ve recently got back into dabbling with NOAA satellites, to that end I’ve setup a test antenna in my bedroom. Initially I was running a Cat5 network cable to it since I wanted to stream I/Q data to my PC and decode there, but it made having to leave my room a bit of a chore so away went that plan. The new plan is to perform everything locally on the Pi itself.
I’m starting to build a Lindenbald antenna. Starting out I’ve cut up some 1″ wide 25ft SAE tape measures from a Canadian Tire sale into four 78″ sections, and folding them like my AIS antenna into four folded dipoles centered approximately on 151MHz, why the odd frequency? NOAA sats are on 137MHz and AMSATs are in the 145MHz range? Well we are relying on the wide bandwidth afforded to us by large conductive surfaces and the folded dipole design.
The other benefit of using folded dipoles in this fashion is their high impedance of ~300ohms, we will be feeding all four elements in parallel with 1/4 wave (at 137MHz) twin lead (again 300ohms) to a single point giving us an impedance of 75ohms which is trivial to deal with from a receiver or transceiver point of view. I’m going to be hooking the twinlead up to some 1/8″ heliax because I got loads of it (and 1/2″ heliax) at the BARC 2016 Hamfest. You can also just as easily put a chassis connector at the deadline at this point for more modularity but that’s up to you.
Here is a quick and dirty guide to making a pretty decent receiving antenna.