We get by with a little help from our friends, specifically Adam Carlson.
Hello, my name is Adam Carlson and I am addicted to learning.
No really, I am, and that is the fun part! Because of my addictions to learning and creating things, engineering and design were a natural fit. If you couple this with a love of aviation, you get an aerospace engineer. Today, I work for GE Aviation designing jet engines, though because I love learning, I did not stop with aerospace engineering. In my free time, I have taken up learning other branches of engineering. I had, for many years, an interest in electronics. Back in about 2010, I was tired of people telling me that what I wanted to do in electronics was not hard, they just did not have time to help me. I asked myself, “How hard can it be?” (Yes, I know that this is a dangerous state of mind when coupled with a desire to learn.) So I set out to learn electrical engineering.
What in the world inspired this desire to learn electrical engineering, you might ask? Well in a few short words: RC submarines. You are probably wondering if I am just trying to pull one over on you, or if they come with working torpedoes. Yes, RC submarines are a real thing; yes, we do have submarine races (it is not just a euphemism); and yes, some can fire torpedoes. As I got more involved with the hobby, the more I saw the wonderful, mechanical claptrap that was used to control many of the systems in the boats. These systems, though, were often unreliable due to their mechanical nature and operation in hot and humid environments. I could see that these systems could easily be simplified and improved upon with the addition of electronics.
It was at this time that I came across SparkFun. It can be hard when you are trying to learn electronics from scratch. At the time, there were not a lot of resources that were easily available. Arduino was really just beginning getting legs, and had not yet achieved the recognition it has today. SparkFun, with its forum, was a great source of learning. Things like, do I use a linear or switching regulator? Where can I get a box of assorted components without having to pay a large sum of money and get 100 of everything?
These things may seem like simple questions to most, but to me at the time, they were not simple. Since then, I have progressed substantially, including becoming the editor of Electroschematics.com. I am currently designing a radio receiver (yes, this has been a very long project) for RC submarines. In the process I picked up a LimeSDR. These are fantastic devices at a really great price point. They have many advantages, including covering a very large bandwidth of signal spectrum. The downside is that it really is just a bare board without the nice finishings of a case. For my application, I plan to use this as a poor man’s VNA. To do this, I need to get a few u.fl to SMA cables, and a few bare SMA connectors to make a standards set (I plan to follow this link as a reference). The case will be 3D printed and lined with metallic tape to give the enclosure shielding properties.
Why go to all this length to get a VNA up and running? Well, for starters, I had a few hundred dollars that I could spare, but not a few thousand dollars to get a “real” VNA. Second, I am addicted to learning. Third, and this is the actual technical reason, submerged antennas not only are too long once submerged, but they go through a change in impedance. There are very few papers out there that will help calculate this. There is software that could be used, but once again, this type of software tends to be tens of thousands of dollars for a license, and that is hard to justify on a hobby budget. So instead, we will go back to old method of using basic principles to get close to a design solution, then use testing to refine that solution. I will let you know what I come up with once I am done.