This is fantastic. I have a friend in Russia who had one of these capacitors in a picture. I cannot contact him so I am glad you made this video. Thank you.
Fascinating stuff. I very much like how you've thought about the aesthetics of the capacitor and how robust it looks. As stylish and manly as a DYI cap will ever be! It'd be interesting to hear how it all comes together.
Absolutely BEAUTIFUL! Such a fantastic display of the marrige of math, geometry, pyshics and electronics. And it all begins to feel more intuitive. It brings my world of acoustic transmission to life.
Thank you so much. I will copy this in full. Could you please post a brief video of your completed and installed capacitor? I am sure many of us would like to see it in action and so learn even more.
I’ve been meaning to make a large air cap for years and haven’t got to it. It would be for a DDRR antenna. My friend made one and uses a vacuum cap (that I can’t afford) and has amazing results with that little antenna. Glad your getting more into hamming around. Keep on tinkering!
TinkerGinger DDRR looks interesting. I’ve never seen that before. I made this cap as an alternative to vacuum variable, as they are expensive as you pointed out. I had the materials on hand, but I’ll bet if I add it up, it’d be cheaper to just buy a vac cap!
Great to see another video from you! I'm in the middle of designing a magloop for my townhouse attic and was considering making a trombone capacitor but I love the idea of using PC boards instead, and you get higher capacitance to boot! Thanks for sharing!
I am planning to build a mag loop of my own for use on 20m. I have ordered a VVC from Max-Gain Systems. Yet I enjoy looking at problems and have been thinking about the tuning capacitor issue. Thank you for showing the math behind this. I hope you will produce more videos as you develop your mag loop.
I like it! You do good work. I was contemplating the idea of using PCB material for a longwave antenna capacitor because it was easy to solder to and much easier to cut to shape than aluminum. (Also, I had a good pile of surplus FR4 material available which is the most important part.) But a friend found a need for the material I had, and with the price of copper shooting up I gave him mine to make his project affordable. So it's back to aluminum for me. But thanks to your project I get to see exactly how PCB plate capacitors will work. You even did the math for me. Thank you. BTW, the material on your workbench does indeed couple the 2 plates of the capacitor and increase the capacitance value. That's exactly how electronic stud finders work.
Wow! This was fascinating! My maths isn't the best but with your help I was able to follow. I was particularly interested because I have a stack of old CDs and was wondering if I could cover them with copper tape, cut them in half and make an air variable capacitor. After seeing this, I may experiment. Thanks for taking the time to make your videos, I for one, appreciate them.
This is a pretty nice and effective way to make a variable cap. I am also facing the same issue as you are, I built a magloop for 20m a while back. It's capacitor was good for qrp txing but not for 25w+ tx. I was thinking of making a variable cap since they can be expensive and not have enough spacing to not arc at those power levels. Good stuff tho.
Thanks Angel. Definitely add up the cost of materials before committing to a design. I sketched up a butterfly version for water jet and it was expensive - comparable to a vac cap. This project is probably also the same cost as a vac if you consider the linear drive mech.
Hello Derek, Thanks for the cool video. It's very interesting to see how the math matches the product. I like the way you explain it. Now i have confidence to make my own capacitor for my loop antenna. Greetings, 73's PD0ONE.
instead of plates you might consider using a coil instead. a tesla bifilar pancake coil can operate as a capacitor in an LC circuit. You might even be able to replace that large antenna with the coil as well and combine them into one. So instead of a large antenna and a stack of plate capacitors you have a single bifilar coil which takes up less space.
Nice tutorial on how to make a high voltage capacitor using blank PCBs, something I've wanted to try for some time. I'm interested in a follow up video to see how well it worked in your loop. It's been said by others that PCB caps tend to drift with temperature so I am curious to see if that was true with yours as well.
Subbed to your channel for the LVDT episode. Yeah I don't know whats going on with your subs, I haven't seen any of these videos since then in my feed.
This is just wonderful.Question for you Derek or anyone else here. Can something like this be used for old tube style radios? Indoor loop antenna does not really work that good so with variable capacitor what can be applied to me needs? Anyone please comment. Thanks guys, scotty
if i want to make a higher capacity capacitor, aka more pico farrads, whats the approach ? just add more plates and larger surface area ? very nice construction you have !! well done ! im experimenting with resonance ! and looking to atain a use'able variable capacitor with say 0-1000 pf or more. but i think 1000 pf is a good start.
Neat build! Makes me wonder about more compact version using mineral oil, like HV transformers do. It won't be such an eyecandy though if you enclose it in non-transparent way (:
I believe that you can double the voltage handling if doing so (or half distance between plates), but I’d imagine it would be sloppy with leaky shaft seals and such. Mineral oils, transformer oils I believe are flammable too.. I have thought of using EDM dielectric like EDM30, but it’s MESSY. These kinds of oils penetrate everything.
I was thinking of a way to make a vacuum variable somehow. And this is weird, I was just thinking of mineral oil. Just now. So would the oil be better than a vacuum? I would opt for the oil if you are using a stepper motor and contain the motor and plates together.
Hello AmRad, I was curious how things went with air variable capacitor for the MLA. I live in an HOA here in Minnesota. I decided to build one for the 11 meter band, although I am currently studying for my amateur radio license. Have you finished your MLA? Thanks for sharing.
It’s pretty much done. I’ll be making a short video on it soon. I’m still playing around with the auto-tuner electronics right now. Keep checking back!
Can you be more specific on the spacers you use? Is it aluminum tube stock? Did you cut these plates? Did you have issues with the shape of the plates when you tested? You got my wheels turning on using PCB board as long as it isn’t too thin of copper.
They’re 1/2” Al non-threaded spacers, had a bunch from another project. I took measurements so far, but haven’t tested full power on the loop yet. Will make a video when I get it all together and stepper control software worked out.
If arcing is a problem, why not use a dielectric in between the plates. Polyethylene has a much higher dielectric strength than air, comes in convenient sheets a very low loss tangent and has a relative permittivity of about 2 - wins all the way around. Am I missing something?
Sure you could. You could use transformer oil, you could use sulfur hexaflouride, or a vacuum, or even some kinds of refrigerant. You didn’t miss anything. I had a stack of boards and standoffs, so that’s what I used.
Hmm... I've been using mine for a couple of months now and it works great. How are you feeding it? I'm using a gamma match. If you email me through my website www.thecurrentsource.com, maybe I can assist.
Hi Derek, I saw a video about using aluminum heat sinks as a variable capacitor by meshing the fins. If you use heat sinks with wide spaced fins, could probably make it a HV variable capacitor. Here's a link to the video. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-SB3ewGXekxo.html 73 WJ3U
Ah, well the loop is collecting dust while I finish a remote stepper controller. The remote driver is working, but the controller is still in the works. Maybe I'll do a video on it as an update. Thanks for the inquiry.
I think your theory that there are 2 capacitors in series is wrong. Adding a dielectric between air spaced capacitors will always result in a higher capacitance, not a lower one.
There are two dielectrics involved. Air and fiberglass. To calculate the overall dielectric, they must be considered individually and then combined.. as series capacitance. I think I pointed out that the capacitance is higher not lower with FR4. (It isn’t my theory)
For crap sake, you are inventing the wheel all over again, high voltage variable capacitors are on eBay some of them are vacuum capacitors for 20kV 25pF to 1500pF, what is wrong with you?
I'm not inventing anything. I'm using what I had on hand to make an alternative. You clearly didn't listen to what I had to say in the video. Pay attention. So glad I'm not making these videos anymore so I don't have to listen to armchair quarterbacks put their two cents in every day. Don't like what you see? Go watch someone else.
