So we come to the final instalment of my current journey along the highways & byways of satellite observation and bring my story up to date. After the disaster that was the QFH antenna I stumbled across this post whilst searching for possible fixes, outlining a simple dipole build. “It can’t be this simple!” I thought to myself, after all the effort I put into the QFH build and now someone’s telling me I can get results with 2 short lengths of aluminium rod! Desperate to get my observation station back online I invested in a couple of 1m lengths of 4mm dia aluminium rod from the local B&Q (I had everything else I needed already) and set about the really simple build. The part that took the longest was the 3D printing of the mast mount.
The images below sum up how easy the build was …
Ironic how the longest post was about a failed antenna build and the shortest post about a successful one! I’m thinking of investing in a low noise amplifier next … after that I may look into a directional antenna assuming I have room to site it in my back garden (I’m thinking possibly not but it warrants further investigation).
Finally, my ground station is named MerCre1 (not too hard for those that know me to work out how I came up with it, plus I think it sounds a little like a name you’d give to a satellite 🙂 ). If anyone feels the urge to check out my observations on SatNOGS you can find me here.
A couple of people have asked about source files for the mast mount. I’ve created a zip file containing the original FreeCAD design file plus the STL & GCODE files, please feel free to download it here.
Thanks for reading, hopefully I’ve tempted 1 or 2 of you to join the fold.
And so begins the bitter sweet tale of Merv’s QFH antenna build … hang on in there until the end to find out why. By the way, I am in no way an expert in any of this. I am a complete noob so please feel free to leave a message if I’m talking rubbish anywhere in the post and I’ll get it corrected.
As you’d expect, there is a ton of useful info on the SatNOGS wiki pages. I’d recommend hitting the first menu option at the top of the page for their Build articles.
After a few observations of various satellite passes and delving into the SatNOGS forums to get a better understanding of what’s what I decided it would be interesting to capture the transmissions of the NOAA weather satellites. They are polar orbiting and pass North-South which fits in nicely with my urban location so I started searching for a suitable stationary antenna design (as opposed to a tracking antenna which is basically controlled by motors such that it can follow the satellite as it travels across the sky … this could be one for the wish list!). The design that kept appearing in my searches was the QFH or Quadrifilar Helix antenna … basically it promised excellent horizon to horizon gain (where you need it most as the distance from satellite to antenna is at its greatest) and minimal signal loss vertically (when the satellite is overhead and at its closest).
After much reading I plumped for the design from this site … disclaimer, without wanting to reveal the outcome of this endeavour, in no way am I laying blame at the doorstep of this website and the design contained therein!
And there it was, standing proudly atop my recently acquired aluminium mast waiting to receive it’s first signals from space. It even survived storm Ciara …
Despite all the effort I put in to produce what I thought at the time was a pretty awesome antenna it never received a thing, bupkis, nada, zero, zilch … empty waterfalls all the way! Early into my investigations of what might have gone wrong I discovered I’d wired the elements out of phase which meant rotating the wire connectors in the top of the antenna tube by 90° … fiddly but simple enough. Great excitement preceded great … disappointment as it still refused to work.
I spent a couple of weeks on and off trying to get to the bottom of the issue, trawling the Libre Space (and other) forums, checking continuity in the antenna, running various tests which had to be on a Linux machine (yet another challenge for someone who’s spent most of his working life supporting Windows!). It just wasn’t to be and the antenna is now sitting up in the roof space of my garage waiting for me to decide what to do with it. I invested a lot of time in the build and I’m loath to scrap it so I might come back to it when time allows.
In the meantime, the story isn’t quite over. Hang on in there for SatNOGS part IV – Return of the Satellite Signal … coming to a screen near you soon!
Before I start, a warning … this isn’t a step by step tutorial on how to make a slim jim antenna, it’s just an insight into how I made mine. I’ll include links to sites and resources where you can get detailed information as I go along.
I think it’s safe to say this is a pretty basic, omni-directional antenna. It’s certainly cheap and easy to make but, like all antennas, you need to keep your dimensions pretty accurate as the relationship between the effective length of the antenna and the wavelength of the signal you want to receive is critical to its operation (even more so with antennas that are used to transmit as well as receive … who remembers messing with SWR meters on their CB radio setup!).
If you haven’t already, swing by the HackSpace website, download yourself a free PDF copy of issue 18 and ‘turn’ to page 110 for a full article by the now almost legendary Mr Jo Hinchliffe! There you’ll find a full list of materials, a proper step-by-step construction guide and some handy links to further information online.
Without further ado, below are a few images outlining my antenna construction …
A while back I wrote a post about my ADS-B setup for tracking aircraft. Around the same time I’d read that it was possible to track and receive signals from satellites but I’d thought it must be far too complicated & involved to do such a thing … until I received my copy of issue 18 of HackSpace magazine that is!
For anyone interested in further reading I’d recommend following the link above and downloading the free PDF file so you can read up a little more on the background to SatNOGS and more detailed information on what is required to setup your own ground station …