Need some advice on physically connecting parabolic wifi grids for remote SDRs - Page 1
Forum section: electronics / rf-microwave

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: January 31, 2017, 09:48:24 pm
content: I started working for a local wireless ISP about a month ago, its a pretty tight company with only a few employees and a few contractors as needed. The owner is pretty generous especially with the gear he started with before he moved to using ubiquiti set ups with antenna/wireless interface/router all built in to the feed horn. What a slick way to save on install labor and feed line loss!Anyways he gave me some pretty long rolls of LMR400 and LMR600 already termed with N connectors, along with a ton of level 2 and level 1 ethernet cable this stuff is bada*s the level 2 has regular foil shielding along with a coax style braid on the outside and a special drain wire (i.e 24 gauge or smaller bare silver plated copper) that you wrap through an eyelet on shielded rj45 connectors. Lastly I scored a router with a custom branded Linux that is more impressive than dd-wrt the thing is this board has 3 gigabit Ethernet connectors and allows me to install up to 3 mini PCI MIMO wifi interfaces.Basically I want to take this gear and build 3 remote SDR stations linked wirelessly bout 10 to 15 miles apart. Each one will be running a feed line that connects to a custom board that has enough 6ghz SPDT RF relays to allow for the antenna types needed at that particular SDR station. This is all wirelessly connected because are local broadband sucks hard and SDR needs a fat pipe. Im looking to try 300Mbit N, 100MBit Ubiquiti radios, or later on maybe some SDR with wide bandwidth running proprietary digital protocols like a USRP utilizing its whole 80mhz channel width.So one station will be pretty simple, just a solar set up connected to a pi3 and RTL-SDR on top of a mountain right behind my house. The other two are at least ten miles away one is on top of a two story barn that has been converted to a recording studio, the other is about the same distance in a different direction on top of a 60ft crank tower. These two locations will be running off laptops of maybeparallella boards, which or basically pi sized super computers! These stations will most likely have airspy's with switchable microwave down converters along with a quad modulator chip for broadcasting data created in GNU radio.Right now in my yard Im in the process of moving a 12ft mesh C-Band dish with a linear actuator system for az, I would like to add some sort of elevation control but im not sure how. Secondly Im working on a bigger version ofthe horn of plentyI have access to mig/tig and plasma cutters at work so hopefully itll turn out nice. Then theres the standard 70cm yagis, adsb antenna etc etc.At the barn location I also want a big dish but this isn't my property, im beaming half of my upload bandwidth to my buddy as a trade for shop space. He builds pro tools plugins for a living and is sick of uploading 10gig at 500k on cable, so he was estatic to get 7mbit of my upload. Basically I need something big and light my idea is to connect 10-20 6ft wide by 4ft tall parabolic wifi grills to form on huge light "dish". I figure if I can accomplish this the reflector will be light enough to go on the roof and be able to be rotated with some motors from car windows and hi res encoders out of some old printers. So first of all is there any down side to making a big dish like this? Secondly how do grills differ from a tight mesh or solid dish, as far as signal? Lastly I originally thought I will use huge washers and bolts to connect all the grills, but that will mean he dishes will overlap a bit causing bumps that will ruin the perfection of the parabolic curves. Im trying to avoid having to use someone elses welder so I was wondering if maybe I could use propane or map gas torch and braze them together. I tested the grills and magnets stick to them so they arent aluminium im sure a small torch can heat the grills the edges are maybe the size of #8 wire or smaller. What I dont know is if regular plumping type soldiers will be structurally sound? Maybe there is a better way to do this? I plan to use the C-Band dish in my yard mostly for astronomy, and the grid dish on the barn for L and S band sats and if possible deep space probes.Sorry the post was long but i just wanted to share my grand plan for an over the top SDR system, and get any feedback on it. The only thing I see that needs improvement is the actual SDRs, but it will be a while before I can get a bunch of ettus radios, I have some test tools to replace first. Although for about 300 or so I could buy the same $160 AD9361 transceiver chip used on the USRP and then make a PCB that will just connect it to a parallella board, then I basically have a pretty good transceiver backed by a quad core arm running linux along with fpga fabric and an 18 core dsp chip.on a side note, im such an SDR nut im working on installing a Mac Mini in my car running linux with two airspy minis connected to my LCD head unit, so I can attach a few terabyte usb drives and record tons of signal for analysis!

author: ECEdesign
author_rank: Regular Contributor
timestamp: February 02, 2017, 04:32:40 am
content: Interesting thread, I am working with some USRPs they seem like pretty nice rigs. The Parallella board is new to me, seems pretty cool.