You look tired today, get some rest. Hope everything worked out for you. Thanks for the video. I'm planning to build a mag loop as well. Your information will help me a lot. 73.
The other reason for using back to back capacitors is that the solder tab for the rotor is typically connected to the actual rotor plates via a slip ring or worse. At the kind of circulating currents you get in a loop the resistance of the sliding contact is significant. (It's also significant on receive.) Usually the rotor plates for both (or many) sections are already connected together, being on the same shaft, a solid conductor through its whole length, so there's no sliding contact in the circulating current path in the back to back sections scheme. The reason that this helps with the hand capacitance is that the frame of the capacitor is usually what is sliding connected to the rotor(s), and that's a sort of 0 voltage point (at least if the sections are the same value), likewise the shaft itself, and those are the things that your hand gets closest to. Balance is key to limiting the effect of hand capacitance, and physical symmetry helps here. I have an original AlexLoop, and yes, hand capacitance is a significant effect. I don't know if the newer models have better balance. I haven't tried yet, but I've wanted to remote the know with a longish non-conductive shaft extension. Someday. You will want a reduction drive. You have a 25 kHz bandwidth at 20m, and you will want to be reasonably centered to get a good match, so, say you need 6 kHz tuning resolution there. The capacitor's range is intended to take you over 29.7-14 = 15.7 MHz in 180 degrees of capacitor shaft rotation, so a fraction of 1 degree is how finely you must tune, Not fun with direct drive. And with a suitable reduction, it takes a long time to go from 20m to 10m. The commercial antennas probably use those clever dual rate drives, where if you go far enough it's 1:1, but when you back up a bit it's more like 5:1 or more, but they're dear. I've been tempted to return to the days of dial cord, with a big wheel (with tensioning spring) on the capacitor shaft, with the cord wrapped a couple of turns around a small smooth shaft that you turn for fine tuning. You could probably turn the big wheel directly for coarse tuning (probably making the cord slip on the small shaft) and use the small shaft for fine tuning, no special gearbox required. I've also wanted to try modifying things as in your first drawing, where the coupling loop is at the bottom, and the capacitor at the top, using a long non-conductive shaft to place the tuning knob at the bottom. So many projects, so little energy.
The reason a single gang moves so, is because the shaft that you are touching is one side of the capacitor, your connecting your body to the antenna, so of course that's going to affect it. with a twin variable you are making the loop a balanced element, and the centre, neutral part is the shaft, so touching it has way less effect. Even using a large plastic knob on a single variable cap won't help that much as you are still coupling yourself in, just capacitively rather that a DC connection, again to one side. I.E, do you hand on to a dipole antenna element and hope that wont effect it's tuning? Unfortunately loops being so sharp in tuning, you cannot get away with anything. For a single variable capacitor try using a good length of fibreglass, or plexiglass rod as a shaft extension so you can adjust it whilst not electrically touching it (or getting too close)
Hi Kevin, just wanted to say the “tuning capacitance” in those calculators is actually the total capacitance to resonate. You can check it 1/2pisqrtLC. The distributed capacitance shown there should be subtracted from the total for the capacitor needed. Only possibly big deal at the high frequency wanted. The distributed capacitance on the calcs is pretty accurate for copper pipe. Good luck and have fun. Looking forward to seeing your finished loop. Stay well.
Good to see you making your vids again, Kevin! This is a rather interesting project, might be something I'll try for 10M since the bands are pretty good these days. I listened in as some guys here in town worked a 10M AM station out of western Canada a few weeks ago, pretty neat. Sourcing the variable cap will be an issue but you've given some good directions for that. Thanks again! de KB9OZE
Kevin, I built my first magnetic loop about 7 years ago. Of course, I made mistakes, but it turned out in the end totally awesome results. You're going to have a blast. I can't wait for the videos.
Thanks for the videos. I find them very informative and helpful. Im just an old Army guy, so i know bullets and grenades, i appreciate your knowlege in the field and opinions. Thanks for the time you take to make these videos for others. W4EMB
if you read the al-705 instruction sheet, it details how to use hand capacitance to tune the antenna... i also use 'reverse' tuning, which means shifting the vfo to lower swr and raise reception...
Hi Kevin I just want to say you are doing so well with all your videos I have been watching for the last few years I have just made a magnetic loop antenna myself also made a video so stop by greetings from Denmark
Hi Kevin, It's Great to see & hear from you again buddy, and I, , , like many others around the world love ❤️ you & your videos. I especially love your dedicated Magnetic Loop Antenna projects videos. This one is Fantastic, & as much, , , , I look forward to the next one, HOWEVER Kevin my friend, whatever your medical requirements and problems are, PLEASE Put Those First, And GET WELL 1ST & SOON. Praying For You. Kind Regards, Ray, aka M0RAY, South East England, UK.
the big problem there is flex in the hose. you need to be really precise when adjusting the cap on these mag loops, and any play in even a stiff rubber hose will make it very difficult.
One does not want different values in the dual capacitor. Yes the capacitance can be calculated, but the isolation to your hand approach will be reduced. Good start. 🙂
First, I hope your medical issues get sorted out quickly. Second, the ARRL Antenna Handbook has the equations for calculating the various parts for loop antenna design. It is personal preference, but I don't like black box calculators. This comes from decades of being an engineer. I want to understand how the various components interact when working on a design. Thanks for the video and take care my friend. 73 de AG7TX
de WB2ZDB Hey Kevin, THANK YOU SO MUCH for going through this, a LOT of this I've been able to glen from NUMEROUS other videos (both yours & others) but there were STILL a lot of unanswered questions which you JUST ANSWERED...THANK YOU AGAIN!!! HOPE & PRAY everything goes well for you and you're able to get back to doing what you want to do & not what you have to do to survive. 🙏 Take care of your self and I can't wait for PART 2 (and any others that may result). 👍😁 Much love ❤️ Brother, 73 ...-.-
Hello! There are equations that you can lookup that will give you the breakdown in air (and other dielectrics. I don’t recommend that you do this but many years ago, I used a 60KV neon-sign transformer on a variac with a series string of high-value resistors (to severely limit current) to induce an actual non-destructive breakdown; of which you can the use an old TV high-voltage probe to measure the potential; short of that measure the input voltage to the transformer, then using the turns-ratio, infer the actual voltage.
Kevin, great video. I want to get a mag loop for receiving here at home. What is the difference between a receive only vs a transmit and receive mag loop? How far should a receive only mag loop be from the transmitting antennas?
Mr. Loughin, is there any way you could post the schematic for your "Rebuilding the L network antenna tuner circuit"? I'm in the process of building the tuner. I know my question is off subject. I'm kinda new at this stuff.
@@loughkb I did watch that video first. I just wanted to make sure I get your new circuit correct with your add on parts. Thanks. Your videos are first class!
Hi, Kevin I am seeking your technical advice regarding a project that I need to carry out to find out if you can recommend any forums or websites where I can find more information on the subject. In a course I am taking, I was assigned the task of building a QRP CW Transceiver that operates in the 160 band, but my team and I have no idea where to start. I have seen videos explaining the operation of a Transceiver in general and how they work, but I still cannot find information that will help me at least understand the basics to start building it. Thank you again, and if you have any information that can guide me, I would appreciate it.
You might be able to correct it by unsubscribing to the channel, resubscribe to the channel and then click the bell for notifications and that should reset the settings.
