A question about practical electrical engineering education - Page 1
Forum section: electronics / rf-microwave

author: profdc9
author_rank: Frequent Contributor
timestamp: April 29, 2020, 04:46:52 pm
content: This is kind of a strange question, but it's something I've been wondering for the past few days because I have been trying to use my downtime gainfully to teach myself RF engineering.I am a Ph.D. in Electrical Engineering from a top USA university in this area (University of Illinois at Urbana-Champaign). However, EE is quite a broad area, encompassing power electronics, signal processing, VLSI, etc. Being very physics and quantum oriented, I specialized in optics and lasers. However I have been interested in ham radio and was first licensed in 1992.But my area is very susceptible to cyclical boom and bust cycles and I have been at times needed to work in other areas. For the past four years I've worked in microwave engineering and got interested again in ham radio and got relicensed. But a lot of the gritty detail RF design work has been handled by those who are better at that, and I have done mostly signal processing.So now I am trying to teach myself RF engineering at home with my limited means and putting my projects at my github site hopefully to help others learn. I find myself making mistakes that I think are probably already known to experts in the area. For example, after a day of studying I figured out that emitter follower circuits have an issue with oscillation and need base resistors or some other resonance damping because the lead inductance to the base forms a Colpitts oscillator with the reverse transfer capacitance of the base, especially with UHF and microwave devices.This is not a big deal, but I wonder if others mostly learn the "hard way" like I do or if most of the experts learn what sounds like obvious stuff on the job. I took courses in circuits at the University decades ago and of course even if they went into that kind of detail at the time I probably wouldn't remember that.Anyways this is probably just complaining but not being a person who studied RF in detail in school I wonder how others came about this knowledge.

author: bob91343
author_rank: Super Contributor
timestamp: April 29, 2020, 05:26:10 pm
content: I hear you. As a graduate engineer, I have found most of my education at the workbench, not in books or schools.For example, I acquired a nanoVNA and spend much time playing with it, seeing how stray impedances work and measuring almost anything with it. I think this has to be the best learning tool I have ever used.I have what, to me, is an impressive array of first rate (albeit obsolescent) test equipment. I soend hours just playing with it. I have some very old gear that still works well, from Boonton Q meters to clip-on dc milliammeters and much other tube stuff. Spectrum analyzers, digital oscilloscope, VNAs, voltmeters, and so on. My total cost for this great stuff has been minimal due to the largess of friends and colleagues and occasional forays to swap meets and ebay.I play with ham radio a lot and just love working DX. About the only lack seems to be companionship to help me over some of the hurdles; my project list is far too long. Most people have strange misconceptions about electronics and even bigger knowledge gaps than I.I have some friends who are into these things as well but their interests seem to me to be trivial. I did convince a couple of guys to get nanoVNAs but only one seems to appreciate this wonderful tool.So hang in there and accept the loneliness that comes with all of these efforts. I am the only one I know who grins with pleasure when measuring a voltage to six digits. Or seeing a coil with a Q of over 500. Or measuring capacitance down into the femtofarads (a femtofarad is one-thousandth of a picofarad).

author: Grandchuck
author_rank: Super Contributor
timestamp: April 29, 2020, 05:49:08 pm
content: Definitely get a nano VNA and a copy of as many ARRL publications as you can. Also, learn to prototype using a copper circuit board and the dead bug style of mounting parts. Ordinary breadboarding is worse than a waste of time.

author: profdc9
author_rank: Frequent Contributor
timestamp: April 29, 2020, 06:31:46 pm
content: So actually I created my own VNA based on EU1KY's analyzer:https://github.com/profdc9/VNAThis project was started before hugen took NanoVNA and started to sell it. I have the performance of the VNA I designed really good now, because I think that the commercial NanoVNA has a number of problems with its design. Most people don't notice these problems but when measuring high impedances especially at high frequencies they become apparent. Also the SI5351A and the SA612 are used out of spec which I found to not work so well because I wanted something reproducible and reliable. But I have definitely learned much by creating this. I also want a design that is reproducible, especially with a known PCB layout and easily obtainable parts as many designs have become obsolete as parts have become unavailable and also one of problems with the NanoVNA has been the wide variation in quality. Also there has not been much attention to fixturing either which is needed for more precise measurements.I can do copper clad and dead-bugging as well as perf board. My manual skills are not the greatest and I spend many hours when I dead bug trying to diagnose bad connections. I use commercial PCB services, especially JLCPCB, extensively. I have been using Kicad because it is free, quite capable, and provides the means to make the designs I distribute reproducible and modifiable. Despite the ad you see in the browser above you (JLCPCB hasn't paid me for an endorsement, yet) their work is great and the main disadvantage is the relatively high cost of DHL shipping, so I try to bundle together several PCBs in the same order to share the cost. I just started to use their SMT assembly service, so it's costing me about $20 to assemble 5 small PCB's or so. The truth is that when I hand assemble something with SMT, I often spend many hours figuring out where I went wrong or have the cold solder joint or whatever, especially with fine pitch parts with many pins. They make it look so easy on the videos but I'm sure those videos are edited.I need to get a spectrum analyzer. I had a Siglent 200 MHz scope and a nice dual output 30 V 5 A power supply. But right now during the virus downtime I'm keeping busy and working on some goal-oriented projects as a way to keep learning.

author: Grandchuck
author_rank: Super Contributor
timestamp: April 29, 2020, 07:16:47 pm
content: Nice going! Your VNA results are impressive.I agree about the spectrum analyzer. The DSA 815 serves me well and I extended mine to 3 GHz with ebay parts. Crude but useful.

author: OwO
author_rank: Super Contributor
timestamp: April 30, 2020, 04:08:20 am
content: Quote from: profdc9 on April 29, 2020, 04:46:52 pmThis is common knowledge to most who has experience with analog circuit design, and yes it's one out of hundreds of things not necessarily taught anywhere and you have to figure out on your own. It's not restricted to emitter followers either, ordinary transistors in common-emitter configuration can also oscillate on its own. You would infer this from the stability analysis taught in university (K factor, stability circles, etc), but even that has limitations:https://www.eevblog.com/forum/rf-microwave/s-parameters-and-stability-analysis/The point is yes, you absolutely need to learn the fundamentals taught in university, but that's only half of it and the rest you have to figure out on your own the "hard way", often coming up with new methods as you go. A lot of "conventional wisdom" in this field are wrong, while a lot of it are correct but only a few will understand why. You can't be an RF engineer just blindly applying methods learned in class and following "best practices"; for example most will tell you that in a PLL you want to use just the right loop bandwidth to get the best phase noise, but in my VNA design I defied that and used the highest possible loop bandwidth, since I know that phase noise from the crystal, common to both the tx and rx synthesizers, get cancelled out upon mixing. If you had simply copied reference designs, followed appnotes, etc etc you'd end up with shit performance (verified on the first prototype).

author: DH1AKF_Wolfgang
author_rank: Contributor
timestamp: April 30, 2020, 08:49:36 pm
content: If you are interested in RF, Electronics and Ham- radio, I would suggest you to have a look into SDR (software defined radio).Also in the Cypress PSoC Microcontroller family. I myself had much fun with PSoC projects, also with Red Pitaya and now with Adalm Pluto.PSoC helps to design a lot of analogue and digital circuits on chip, without soldering iron...DD4WH made a nice SDR receiver with the TEENSY:https://github.com/DD4WH/Teensy-ConvolutionSDR/wiki/Links-&-ResourcesBest regards, Wolfgang (DH1AKF)

author: profdc9
author_rank: Frequent Contributor
timestamp: May 01, 2020, 02:35:28 am
content: I have been mostly using the STM32 family recently because it is so widely available and there are now manufacturers selling similar processors (e.g. GigaDevices). I used NXP for awhile but most of the stuff I wrote code for is now not recommended for new designs/obsolete (ARM7TDMI-based). I would like the stuff I put up to be able to be buildable for a long time if possible, as many previous VNA designs have become obsolete because their parts no longer can be sourced. Especially the STM32F1 / STM32F103CBT6 is so common and cheap nowadays that I use it if the application can get away with it.I spent a long time analyzing the phase noise of the VNAs and came to the conclusion that the best way to avoid cumulative phase error is simply to trigger the ADC off the IF signal directly. This allows for long integration times, similar to how a lock-in amplifier works. A lock-in amplifier is one such device where the cumulative phase error is removed because the signal used to modulate the signal is directly used to also demodulate it. In a manner of speaking, a VNA is just a lock in amplifier where the phase or delay of the reference (LO) signal is modulated relative to the reflected or transmitter signal (RF), and the interference between the reflected and reference signals (IF) is measured. This is exactly what is done in optical heterodyne interferometry. and works in the hundreds of THz frequencies. An optical interferometer can be set up as a "vector network analyzer" of optical components, measuring S11/S21 etc. This approach is also used at milimeter / terahertz frequencies for which a mixer is not available and only a square-law detector (like a Schottky diode) that can detect power is available. For a while I was working on trying to use this approach to make a simpler VNA. All you really need to do this is an oscillator, a phase shifter that can shift the phase a small amount (or equivalently a small delay), a directional coupler, and a square law detector.So I came at making the VNA with a different perspective because I built optical instruments. This was a writeup I did on a method I found of just using diodes to find the phase and amplitude of a reflected signal. I tried it, it works, but at the time my tandem match was constructed poorly. I could probably do it much better now.https://drive.google.com/file/d/0BwFicJLV0O4jb1FtYW40ZjMwWTQ/view

author: radiogeek381
author_rank: Regular Contributor
timestamp: May 01, 2020, 02:00:22 pm
content: I had a very similar experience: PhD, MSEE, BSEE, all from good programs. And they made my career.But most engineers (me included) get their toolsets from school, and learn the craft at work. The luckiest learn from a good mentor, or from colleagues. This amounts to going to school on the company dime, but most larger engineering organizations recognize that, and build it in to their hiring and development plans.My last degree was squarely in Computer Engineering, but by then I'd had a lot of experience with production quality hardware design. But the "j-omega" stuff was not a natural place for me.When I got back from gradual school to a job in processor design, I connected with a friend who was an avid and very experienced microwave ham. We built a bunch of radios and antennas together, and it taught me a lot. So, you are likely on the right track: if you can't learn it from work, learn it at home. But it helped tremendously to have a mentor of sorts. (I also learned a lot about hard-core engineering by taking things to freezing mountain tops and sweltering beaches.)Good luck.

author: frogg
author_rank: Regular Contributor
timestamp: May 01, 2020, 02:18:05 pm
content: QuoteI think it's fair to say that aside from a few electives which you can teach yourself, you've received as much formal education in RF as most RF engineers with BSEE degrees. However, MSEE or PhD's in EE have more specialized education will have more formal education, but this is almost always tied to practical labwork.Therefore, in my experience, RF beyond the BS level is learned "on the job." This is because there are a lot of RF jobs that require lab resources far beyond what an individual can purchase on their own. It really prevents people from learning "the hard way" as you put it, because it's not like they can just grind it out at home. The equipment required is just too expensive.For example:1. High Power RF: High power RF is usually work in accelerators, or anything using klystrons in the 1-10MW range, high vacuums, large waveguides, superconducting filters, and complex cooling systems.2. Radar: What makes this inaccessible to most folks is the need for very high frequencies and high powers, which makes all test equipment and signal processing devices very expensive.3. Cellular: Similar to radar, much lower frequencies, and much lower power. This means that the base station receivers have to be very sensitive, requiring complex filtering and superconducting devices.4. Medical imagingThe good thing is that I've found most RF guys are actually really hands on and love to share their knowledge, as long as the work environment supports that sort of arrangement.

author: profdc9
author_rank: Frequent Contributor
timestamp: May 03, 2020, 04:11:49 pm
content: This will probably surprise few of you, but its simply astounding the cost of some of these tools. I am working with a company that needs to use Cadence, and a seat of that software for about a year is about $200,000. Ouch! Just to get into this game is really expensive. The same can be said of ADS, HFSS, Mentor, etc. Commercial software is not a bad thing and programmers need to eat but it is a high barrier to entry. It's why open source tools can be so helpful here, even if they are going to be vastly inferior to the Keysight/Rohde and Schwartz/Anritsu offerings. You know how they say that the next Einstein could be in Africa or Central America or some other impoverished location so that talent will never get the chance? I think about the fact that I was as well as taking advantage of opportunities I had, I had them in the first place because of the birth lottery. And maybe to go off on more of a tangent here, if the tools to invent aren't in the hands of individuals, how you can you have a free society as the technology on which we all live depends on means that only a few control? It's one of the reasons I think ham radio is so important, because it encourages individuals to become technically proficient and invent, and this is one of the main reasons I think ham radio is important today. You can communicate instantly so many ways and so that wireless communication is no longer the unique way to do this (and amateur radio is certainly not the easiest way to do it), but the means to understand and manipulate the electronics and software is something that needs to be widespread and with as low of a barrier to entry as possible. Widespread technical proficiency and means is a check on the centralized technological power and control on which modern society depends.