Ham Radio - A simple magnetic loop modification with a big improvement!
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- Опубліковано 25 лис 2017
- The first simple change I've seen to really make a difference in magnetic loop performance.
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Yes, this is a great experiment which proof an improvement. Thanks for sharing this helpful information for HAMers.
Great video, thanks!
The two loops are supposed to be coupled magnetically. The described technique increases the capacitive coupling, not necessarily the magnetic coupling. Not that it won’t work, it just decreases the useful deep nulls and introduces other uncharacterized modes of operation. It may increase common mode currents on the coax. I find that if I increase the size of the round coupling loop and rotate it within the plane of the loop I can achieve a perfect 1:1 SWR without introducing other coupling modes.
73 de AA5TB
What would happen if you replaced the magnetic coupling with a capacitance coupling?
The magnetic flux density is lowest in the center and highest near the loop. Integrating flux density across the area of loop is how the magnetic coupling strength is determined. Moving more of that area away from the center increases it. The magnetic coupling vastly dominates any capacitive coupling in this configuration.
Thanks for a very nice and helpful video. Your presentation, instrumentation, and clear explanation are really easy to follow.
Kevin, you're a star. I can't wait to try this. Thanks.
Kevin, the "squashed football" coupling is really cool for the portable loops. Between the capacitor adjustment and the "squashed football" you can really get the magnetic loop on the right track. Good video.
I've played around for a couple of years making mag. loops and came to the same conclusion that squashing the loop helped to reduce my SWR. I even experimented with a tiny loop for 2 metres.
Bill, G4GHB.
One must be very careful when it comes to coupling tuned antennas/ tuned systems, as there are a few issues involved.
1. Soft coupling will permit the tuned loop to oscillate at its natural frequency while a hard tight coupling would FORCE the tuned loop/system to be driven too forcibly by the source.
2. If the coupling loop is placed at the centre of the much larger loop, then the EFFECTIVE magnetic coupling is very small as if we look at the resulting magnetic field cutting/curling the larger loop, then using a drawn diagram on the flat paper, one needs to consider ALL of the existing magnetic field in the inside of the small loop coming up while the magnetic field outside the coupling loop going down. Only some would curl the large loop. So while the coupling loop is at the centre, the upcoming magnetic field will cancel some of the downgoing magnetic field and the " difference that couples the larger loop is very little. The full tight coupling will only occur when the coupling loop is the same size as the actual loop antenna.
By flattening the loop to have more parallel lengths of the loops running together and this is a tighter coupling, but one must be careful as the larger loop is now being FORCED too much by the coupling loop and so it might lose its resonance peaking quality.
Normally to let the system resonate freely, light coupling is desired, but this will not result in maximum Power being coupled but light coupling will retain the good quality of the peaked resonating unit.
FORCING naturally resonating systems with tight driving is not desired even in musical instruments and the instrument must be plucked or blown with light coupling for the pure note of the system to emerge. The quality of a system even in using tools is so important and when using a hand saw, one must not force it to cut, but one must feel the natural pace and let the saw cut by using the natural weight of the saw rather than forcing it to cut at all costs. The latter action loses the quality of the cut. In feedback oscillators, the feedback must not be greater than necessary as the oscillator will not resonate with a pure sine wave or harmonic motion but it will have a different waveform as the system is FORCED too tightly!
Many students try to resonate a parallel LC circuit from a voltage source and they do get a surprise when they find that the LC parallel oscillation does not peak as expected. A parallel LC resonating circuit must be driven by a perfect current source for it to resonate freely. Unfortunately, practical sources driving loads are not as ideal as we like them to be and the matching difficulties do exist where one cannot expect the ideal situations in practice. Anyway, if one goes too ideal in tuned circuits, they will go off tuning so easily at the slight less variation from the ideal state.
Just got done watching your video on squashing the inside of the magnetic magnetic loop and was very impressed and when I build my magnetic loop I am going to use that thank you very much
Thanks for the good info about the mag loop, fixed a problem I was having with swr not going below 3.
I am getting into mag loops, thanks for the info. Neat looking home brew!
Kevin, I made a 3' diameter round loop with the Faraday Coupling Loop and also one with Gamma Matching. The Faraday version really responded to "squashing" in the higher frequencies of the usable range. The Gamma Match needs to be set in the middle of the tunable range of the capacitor; in my case it was ~18MHz (my capacitor allows me to tune from 6MHz to 30MHz). The Gamma Match when finally set is less fussy across the entire range at resonance ~1.2SWR but the "squashed football" could actually be "finessed" to ~ 1.0SWR. They both work fine, but you have to be patient with setting and soldering the Gamma match because it takes a few iterations. The Gamma Match point is typically 8%-10% of the circumference (mine was 9.5%), so in my case it was 113" x 0.095 (9.5%) = 10 3/4". I did not test (like you did) with a Field Strength meter. Keep up the good work and safe travels!
thanks Kevin I will be adding that to my best practices loop build in my head.
Wonderful presentation! I made a coax loop antenna when I was a kid that was a a spaced helical coil on a wood frame and I could tap into the various turns for various bands. I could use it for AM DXing since I could null out the loud stations. I could not understand how it worked but it was fun to watch it pull in the stations when the cap was tuned just right. The coax was one complete turn right on top of the helical coil all the way around.
Your experience is very interesting. I've been doing a lot of research on the magnetic antenna loop for a long time. I've done many, but I haven't noticed the difference between the distance between the two loops in the swr relationship. I currently have 1 meter in diameter. I also made a field effect meter to adjust the best performance. I used another process with the smaller loop with a round ferrite and 5 turns of rigid wire.
Wow very cool tip -- THANKS. Our radio club just had a presentation last nite on these magnetic loop antennas. I'm new to HF and had been trying to figure out what to put up for 80/160 meters, and this seemed a very cool way to go. Just checked Craigslist here and found a vacuum variable of sufficient ratings and heading out tonight to go pick it up. Will be doing some studying on these antennas and collecting materials. 73's RH
I am collecting parts to make a magnetic loop. I will definitely try this improvement. Much thanks!
Just did this to mine with excellent results. Thanks.
Squashing works because, by widening the distance where the loops are in close proximity, you increases the number (actually, the percentage) of magnetic lines from the feed loop which couple to the main loop. Remember, only those loops of magnetic force which go through BOTH loops act to couple the loops. The more you squash the loop to increase that close proximity, the more you reduce the area enclosed by the feed loop. There comes a point where increasing the distance of close proximity (by squashing the feed loop) is offset by the reduction in area of the feed loop caused by squashing it. (the number of lines of magnetic force is proportional to the area enclosed by the loop, so you want balance the area of the feed loop, with the amount of coupling to the main loop. A perfectly circular feed loop has maximum area, but a fairly small length close to the main loop, as you point out in the video. A feed loop squashed so that it follows the outer loop as far as possible before closing on itself (with a straight segment) would have a lot of coupling, but reduced overall lines of force, due the reduced the area of the feed loop. The optimum amount of squashing of the feed loop will occur somewhere between these extremes.
What if you distorted the outer loop instead? Bent it to make a closer match to the inner loop?
This sounds like a good modeling exercise to figure out the best possible shape of the inner loop. Of course, you can just tinker with the shape for hours until you maximize the performance. I'd be curious to learn what the negative impact is if you squash the inner loop to it's extreme.
Increase the diameter of the inner loop: same effect.
I very much enjoyed your presentation on the "Loop Antenna" - I plan to purchase a magnetic loop and also try to build one ... Your presentation got me back to the loop - great job ... 73 N1TOV
Videos like this are priceless.
Liked and subscribed, very informative. I haven't started fiddling around with loops but I'm keep that bit of information in my head for whenever I do ;)
oh I commented on this a year ago ;) I was just about to ask: some loops have a gamma match which utilise this concept, the whole radiating portion is parallel to the big loop to maximise coupling. Have you looked into this too? I'll start building my own in a bit!
I wonder then if gamma matching would work better for transmitting then a standard coupling loop since more area of the gamma match part could cover more area than a squashed ovoid coupling loop.
I too have found that small loop squishing helps to get a perfect 50 Ohm match. Also, that the required amount of vertical squishing or stretching of the small loop differs slightly on each band to maintain a perfect match.
good to know this. May try to build one myself.
Hi Kevin,
Thank's again for another interesting factual video. Keep up the experimenting and modifications with the Mag loops. I will get round to building my own eventually and should know what to do after watching your videos on the subject.
73 de John. G0WXU
Amazing tweak!
Most of the high couple folks use a big type 43 torrid around the bottom with 10 turns,
I have an AEA IsoLoop 10-30MHz that I bought about '93 or '94. It has a massive capacitor and works up to 150 watts. It had some mechanical issues with a plastic coupling to tune the capacitor. That was fixed. They recommended putting the capacitor on top if vertically mounted, made it very top heavy. I'll have to get it out of storage but I think that the coupling loop was shielded with a gap in the shield. It uses a stepper motor to drive the capacitor. The main Loop is a 2" wide 36" diameter aluminum band welded to the capacitor. Very narrow bandwidth and it was tuned by listening to the receiver noise(max). I think that they may have made an automatic tuner for it too.
Excellent info, thanks!
Thanks for this info,thats correct and you can see it by using a graphic analyzer.some times the resonant point is perfect but the Z is to high or to low. I make the tuning capacitor allways on the top because here is high voltage and nothing must be in the near.....73 DH7TB
I can confirm that there was difference also in my case when squashing the inner loop to form an oval shape. The difference in my case was obvious on making the swr closer to 1:1. I can't comfirm that there was significant rx/tx improvement though!73
this was used first in the Zenith Clipper radios, back in 1942. The guy who made the project of this radio noticed that the RF signal is a lot stronger on the edge of the loop (in that case, round battleship and airplane window) than at the center, and if the antenna is oval, the reception is even better. It's funny how this was forgotten and was rediscovered just recently :)
Fascinating...We're entering the realm of the SLOT antenna here. Worth reading up...Maybe the loop is related to a 'skeleton' slot...very commonly used!
73 G3NBY
oval or egg shaped with the narrower edge on the top?
@@MauriatOttolink No, the slot is quite a disparate antenna - basically being two shorted 1/4y transmission lines (one long one and one short one - from the feedpoint perspective)
Very interesting and informative. Thanks!
Hey Kevin. I can confirm you're findings. I repositioned the coupling loop of my 90cm loop (40-17m). Since I flatten the couple loop the efficiency on 40 and especially 30m has gone up noticeably. Thanks for this great tip! 73 Werner PA3GYV.
makes a guy wonder why commercial loops dont incorporate such an easy mod?
@@patmb2011 The commercial companies would more than likely add another £100 /$100 or more on top of the price for such an easy & simple thing like that.
Nice video!
Very good to know - thanks!
Thanks a lot, you see
When talking about Radio
And concerned systems,
A related circuit diagram with polarity etc.. is a basic
Requirement,، I witnessed many other channels on the
Topic,,,,and found the difference that really maters....
I have heard that it can also be excited with a ferrite toroid, which perhaps makes the coupling between the coaxial and the antenna easier
I have tried three types of coupling, including the ferrite. I didn't find any real difference in performance between them.
Very Interesting. Instead of the copper flashing (or whatever you used for the small loop) what if you used a large coil spring to form the small loop. What I'm thinking is the coil spring as the small loop. Fix the edge closed to the mail loop. At the opposite side of the small loop attach it to a sliding bracket mounted to your support. The thought being attaching it that way: 1st when you compress the inner loop it should deform symmetricly (may or may not make a difference) and 2nd it provides a fine tuning adjustment that may help when switching bands. If it does than it should be easy enough to make a remote adjustment system. I confess that I'm totally new to SID antennas and am building my first now so I'm looking for a good coupling method that will provide the best performance over the wavelengths I'm targeting (40M - 15M0). Any thoughts?
Thank you for sharing. How about other shape of coupling loop? For example, make it slimer to just go along the big loop?
Excellent video, thank you,
I remember years ago while in college, I had read a paper on the effects of the change of shape on the emission of magnetic waves. (It was probably written about the time of Tesla (he did not write it) and his experiments on radio energy transference.) The slight changes of the shape from circular pattern will direct the magnetic field in a more "broad" pattern. That would explain why a squashed inner loop works better.
73
Moe k2jdm
Something to try, sure looks promising.
Howdy. Nice.
Experimenting with my CB loop. A circle driver reulted in no better than 1,5 swr. An oval driver improved the swr to about 1,2. However, with a gamma match the swr of 1 was actually achieved.
Regards.
The indication on the signal strength meter almost doubled in numbers when you squashed the smaller loop! Pretty impressive!
+unklewink well it's response isn't quite linear, but yeah, a good difference.
That's why I mentioned the numbers. Of course, the actual radiated power would not be doubled.
Hi that was a fascinating demonstration and video. Could I just ask you have you noticed any difference in improved reception performance after this simple modification to the coupling? Or does it go without saying that the improved s w r and r f output also increases reception efficiency? I am a big loop fan and constructor but only use them for swl these days. 73 Adam M6RDP
Thanks for the video. I'm trying to find the video where you made the loop antenna in the first place, could you provide a link perhaps? I got my Ham license at 14 and didn't do much with it. I just bought a Nooelec SDR and would like to play around with some homemade antennas.
Thanks Kevin. I'm fascinated by the implications of how this effect apparently operates. I'm curious to know what kind of effect it has on the overall bandwidth of the antenna at any given capacitor setting. In other words, does it act more like a narrow pass filter or hopefully does it broaden it? Obviously this could have serious implications for the method used for modulation. I'm curious what would happen the loop coupling if you put a high voltage dielectric insulator between the loops so you could minimize the gap between them yet stay electrically isolated? That's taking proximity of the coupling to the extreme so to speak. It's got me thinking about how to mathematically represent the effective gain through the magnetic coupling between the conductors. Thanks once again, you taught this old dog a new trick. The day you stop learning is the day you die.
Good Video Kevin; really enjoyed it !!! 73
Very interesting. Thankyou.
Hi Kevin, I’ve got the MFJ-1786 mag loop, I’ve adjusted the coupling loop before to football-like to more circular, but that’s when it was horizontal in the attic. I’ve had it vertical and outside for about a year now and it’s probably time to fix it. I have problems on 15 meters getting it any better than about 2.5 or 3:1. Would love to hear any thoughts or advice you have about optimizing the -1786. Love your channel, keep up the great work! Jeff, KF5KWO
I don't have one and I'm probably not going to get one but still it's a pretty cool video and some good information.
Your field strength indicator should really be in the far field of the antenna to prove that your antenna has indeed experienced an improvement.
Thank You Kevin! I am in the process of building a loop for 20 meters. I also built a VLF (wire) type 4' square loop to receive European LF AM broadcasts and SAQ (Sweden 17.2 KHz). I tried covering the loop wire with aluminum foil to form a magnetic loop taking the signal off the outer Al foil feeding it to a low Z input preamp (common base 2N3906). The resonator is the wire loop with a 4 section variable (and add C for LVF). The resonator is not connected to the preamp (just the outer Al foil. I found much improvement on noise and directivity...just an FYI from N3SWL Thanks again Kevin!
Great video. Do you have instructions for making this nice Antenna ??
Great video, I'm going to incorporate this idea in my next loop antenna, thanks
Yes, I have had same results with my magloops. A section where the feed and radiating loop are close and nearly parallel improved performance significantly. My interpretation is that this is because more H field lines overlap the two conductors improving transfer of power. I have only moderately ovalised the feed loop so not sure just how far you can push this effect before capacitance problems in the feed loop could emerge (ie. One side too close to the other).
Of course capacitance exists. What matters is what is effective. The added capacitance probably lowers the "Q" which is why the bandwidth broadens. That's largely okay or at least irrelevant. If you have a 1:1 SWR, then 40 watts into the antenna means 40 watts radiated OR potentially lost as heat in the loop itself (you can feel how warm it gets, or doesn't).
Hi Kevin;
Interesting results, thank you for sharing ...
I really enjoy your videos, and especially the simple and elegant ways your build experimental stuff.
I've been playing with these for a while now, all be it with very limited measurement and fabrication means.
I've built an active receiving loop with a 4-turn 28cm OD, 2mm solid copper outer loop and 8 turn coupling loop.
It is tuned remotely via a varactor (getting rid of common mode RFI picked-up by the control line was very challenging ).
Do you think squashing the 8-turn coupling loop would improve things in this case?
Best 73s.
OD5VL
Very interesting modification to the loop Kevin as it seems to increase the power radiation of the loop =)
Did you push this to its logical conclusion, which would be an extended D shape, rather than an oval?
Or a full diameter loop stack, yet have the couple loop feedpoint at top of loop, and where that is the normal couple max, it is instead spread around the tuned loop, because it is always best to have the feedpoint at highest possible. These coupling tweaks might effect the cool "endfire" directional properties on recieve and tx, giving it some extra disgretion for portable operation, but setting up h.o.a. stealth, you will not be playing telescope, just as much power emitted possible, and as broadband as possible.
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I would try wrapping the pick up loop around the main loop. For maximum performance. Just maintain a air gap between the pickup loop and the main loop.
Hi Kevin, Nice improvement. I'm using in my loop (20 to 40) a gamma match but I'll try this solution you describe.
Did you tested the gamma solution vs the induction solution?
Regards
I've built loops using four different coupling methods. I never noticed much difference between them.
I wonder if spacers could be made to hold the inner loop equidistant to the outer along a certain distance, though I don’t know how much that would matter.
Great information, thanks for posting the video. One question... Is there a limit to the amount of squashing of the inner loop? For example, what happens if you totally squash the inner loop so that the maximum surface area of the outer loop is in close contact to the inner loop? I'd imaging there's a point of limited benefit and/or perhaps some inefficiencies introduced by having the inner loop too close to itself.
hi...I tried it almost completely squashing the loop, im not sure about the Efficiency but the SWR definitely went way down to 1:1.03, only thing i did notice was that i had to reduce or increase the squash minutely like a Centimeter or so to reduce the swr to 1:1.03 or less for different bands...mine is 80m, 40m, 30m and 20m...with tiny adjustment of coupling loop...thanx
Hi Kevin.. I am constructing 2 loops to get around some noise.. I have hard line and heliax laying around, so I made an 8 footer (diameter) out of hardline,, and a 150 inch (circumference) out of heliax. I am interested in the meter that is on this loop. Was it something taken out of a radio ???
This is absolutely fascinating and it goes to the question of how best to couple a mag loop. I note that others have used gamma match devices which then allows them the opportunity for additional tuning at the level of the coupler as they lengthen and shorten it.
It appears that you could also essentially lengthen and shorten the outer loop proximate portion of your coupling loop by "squashing" it. Perhaps there is a "best squash" for different bands ?
Very cool. I just built my first mag loop using a road bicycle rim. I'd going to try this mod with it now. Thanks! Question. Does it matter what orientation the tuning cap and coupling loop are? I mean top to bottom? I have my cap at the top and the feed at the bottom cause I found it easier to keep the coax away from the loop when it's at the bottom.
Yup, big improvement! Thanks!
What with a Chameleon if I deploy more the mast and have the coax following the inner circle on a little more length ? Or is using the aluminium external circle instead of coax still better ?
One hell of a difference,so important when using only low power de M0ANO
The coupling loop is half of a transformer. We don't have the windings of a transformer across the room. Coupling is everything, signal strength, the lot!
Hand capacitance from not having a twin gang capacitor.
Hi Kevin Eddy again please i want to replace on my MLA the small ring by a ferrite core FT240 mix 43 is good option for 20 & 40 meter band or i have to use FT240-43 Thanks in advance Eddy from Florida!!!!
Would shaping the outer loop yield similar improvements vs deforming the inter loop? My Chameleon F-loop 2.0 has a rigid inner loop. Thanks for sharing. KE0UWN
Kevin, this works on my Alpha Loop Jr, SWR dropped a bit just by "squeezing" inter loop some......good find!! 73 ~ k6sdw
Where did you find your RF meter?
Hi Eddy, if you're asking about the meter in the middle of the loop, that's a basic field strength meter. I talk about the circuit in my video on building your own.
ua-cam.com/video/8Dd0oEzDepA/v-deo.html
There is an optimum coupling to the resonator, initially was undercoupled. Making the driver loop bigger will have the same effect.
Thank you.
Thanks Kevin, that was great information, I can't wait to start playing around with my loops again now to see if I can do the same thing. Might have to wait until next summer now though. Good info! 73..wd0akx
I'll be interested in seeing what you find. If you do a video on it, be sure to let me know.
Great job Kevin !
Привет KEVIN! Спасибо за материал. Я доволен работой данной антенны, применяю с 2019года. Имею QSO со всеми континентами. Очень доволен работой, магнитной антенны.
С уважением. 73 de TOLY. UN9PI
Wow well what a simple adjustment and if it was squashed a little more would get better and what is the trade off but brill kevin you made a lot if hams happy chaps and ladys
73
G0myd
I'm already thinking about making a jig with a flexible conductor so I can change the 'squash' in real time and make measurements. I want to find the optimal degree of deformation for this loop. I suspect it will vary depending on the overall loop construction.
Is that the same field strength meter you made in another video? I plan to add that one to my Mag Loop antenna. Just wondering.
It's the same circuit, two diodes, a cap, and a 10K pot.
Interesting and good information. 73
I figure the "squashed loop" gives a better ratio between the TX 50R and the loop itself? Maybe a smaller/larger coupling loop (but still round), would achieve the same? I am in the middle of building a loop antenna to transmit on 2M... (To fit on the top of the HT!). 73 de Stan, G4EGH
Hi kevin another great video. I made a RX loop with a preamp and I'm having some problems, can I send you some pictures of it to see if I did it right?
My email is good on QRZ.com.
some great info, only problem I am having is all the calculators and info I have found gives me the size of the main loop for a given freq but I can't find the size of the coupling loop, the relationship between the two, ex 1% or 10% the size of the main loop.. thanks Steve..
Steve, from what I’ve reviewed the coupling loop (or smaller loop) is symmetrically placed inside the main loop (larger or resonant loop), and the size is about the size of the larger loop’s radius, or equal to 1/2 the main loop's diameter or ≈ 1/6 the loop's circumference, or somewhere in between 1/3 to 1/8 the circumference of the larger loop. Hope it helps.
73 de KG4QYY
What principle governs the relative sizes of the two loops?
Nice video, where did you source the AL tubing to form your loop? Thanks.
Wheel chair handles.
Very interesting and thanks for sharing! Did you compare bandwidth too?
It's the same. If it were wider, the efficiency would drop. The extremely high Q of this antenna is the reason it works as well as it does.
Seems to be a lot of room for experimentation. Looking at your inner loop, it appears to be a copper pipe, which you mentioned, squashed with side facing the outer loop. I'm wondering, first if edge on would be better or worse , and secondly if the crushed pipe has a lowered efficiency due to basically presenting a double layer for induction even though they are not isolated? And with a longer line of close contact in your experiment does this not mean that the resonant tuning is not so precise?
Mag loops have always fascinated me, never built one though.
I was thinking, if it is an increased surface area that's improving the loop, would building an annular space inside the outer loop and inserting the coupling loop into it, result in the maximum surface area and the greatest improvement?
QED
another great video . i have the mfj 936b loop tuner technically not a mag loop but i found the same using coax i get poorer result then i do using a tape measure ( easy for portable ) ...2E0FOK
Dave Sutherland hey I have same loop tuner and with the measuring tape is a breeze!!
sure is. The only size i have not tried as yet is for the 80/75 mtrs (63ft) as my tape measure not that long
"i have the mfj 936b loop tuner technically not a mag loop" I have encountered this misconception in several places. I also have this tuner. What makes an antenna a "mag loop" is a radiating element shorter than 1/4 wavelength and a very high circulating current that accentuates the magnetic field. Magnetism is created by a loop of wire and the strength is determined by current. So a mag-loop antenna has a high circulating current. That's it. How you couple or "excite" the loop does not make it a mag loop. You can inductively couple or capacitively couple and gamma matching also works (which is a combination of inductive and capacitive). True gamma matching is difficult to achieve because where exactly you attach at the loop depends on various factors.
The MFJ style of capacitive coupling works well because of how easy it is to adjust the matching capacitor.
For the experiment you could try to maintain the round coupling loop but move it UP so its sticking a little bit above the main loop. That also would give more coupling. It would be interesting to see how that influences the field strength meter and the SWR
Wow, what a great discovery. Thanks so much for sharing. 73 VE3VCG
I see your "earthy" point of the coupling loop appears to be insulated from the neutral point of the loop itself. My old AMA3 had a hefty earth link between the two. Have you looked into this? Will G0OPL
Thanks for this tip, I have been putting of building one because of the supposed low efficiency of the smaller loop on 40 mtrs, but this tip deserves a shot.. VK3HJW
Maybe increase efficiency with a very tight coupling using a ferrite toroid configured so that the radiator passes through for 1 turn and enough turns on the 50 ohm side to appropriately match the impedance. Just a thought. . .
I used clamp on, Split fer-rite ring on the main loop and just 1 turn connection to the feed coax was best. (1.4m diameter loop for 80, 40, and 20metres) very close to 50 Ohm and that can be tweeked by a tiny shift in the resonance capacitor.
Hi Kevin, im into swl, is this type of antenna useful for SWL?
What if the receiving/transmitting loop were to grow to be slightly smaller then outer loop? Such that there was only 1/2" between the inner and outer tuned loop all the way around the loop? essentially a ring just inside of the other ring?
Hi Kevin. Thanks a lot for your sharing. I'm also a loop's fan :). I've already noticed something like that. At this time, no field strength available in my shack. (I like your den, it seems to be like mine... Many items ensure the decoration). Have fun from Switzerland - 73' HB9HFJ.
You should try the Par End Fed , no loop buy performance wise 20X better than a loop www.lnrprecision.com/store/EF-10-20-40-MKII-p39885458
Yeah, but can you rig an 81 ft wire on your dinning room table
Many thanks Kevin. That was very informative. Did you find any difference in Q? Was it the same, or broader, or less bandwidth? I have an MFJ 1786x & it's in my kitchen. It is hard to tune it on the 17 metre band for some reason? Kind regards.
73 de Pete GI0FZT.
As I recall there was no change in bandwidth. Thanks for watching.
What if you integrated the coupling loop into the middle of the outer loop like a 2 turn coil one small and one large, and drive the small loop at the points where they pass each other, 1/2 turn to small loop and then remaining 1/2 of the large loop. Like an double ended auto-former. auto-former Driven in the middle. Some thing to think about???
Hi Kevin, great video! I haven't built a loop but I want to try. What do you do with the inner core of the coax of the main loop? I understand you connect the braided outer mesh of the coax to the tuning capacitor. Do you just leave the inner single-core copper wire cut and insulated? What if you removed that inner core and just used the mesh around a plastic core (with copper wire inside)? The reason I ask is this... imagine if you could make a slit in the insulation at the top of your main loop and remove a portion of the inner core from the coax on either end and make your smaller coupling loop out of the actual inner core? Then you would have the inner core INSIDE the mesh, extremely good coupling!
For the outer loop, tie the shield and center together. The lower the DC resistance on that outer loop, the higher the efficiency.
@@loughkb Thank you! I will strip the coax at several points along the length and solder the inner core wire and shield to each other. Thanks!