It is tidbits like this that make life so much easier for many of us that have been hesitant when it came time to make that final bit of tuning for fear of destroying an antenna that looks good on paper, but is just that little bit off.
This experiment should encourage everyone to try adjusting their (isolated) wire antennas just by wrapping back the excess wire. The folded back piece of wire, as long as it’s close enough (and it usually is) to the main wire, takes the RF - inductively coupled - with it and doesn’t affect the expected properties much. It works, that’s all we want. Only if you want to get overly precise, you must take the foldback into consideration as a kind of capacity hat, which makes the antenna electrically a little bit longer. The higher your frequency, the more you will notice that effect. Thank you very much for this highly instructive video! Vy73 DB6YC
Hi Dave. I feel I have something to contribute here. It concerns small backyards. When I first got my license I went on 2 meter nets and explained that I had only a 30 x 15 ft backyard. There is also an unhelpful very tall inaccessible spruce tree in the neighboring yard. Declaring this on one of the weekly networks an Elmer showed up. My Elmer suggested an vertical he found on Ebay. It worked somewhat but I noticed that he had an MFJ 1775 rotatable dipole that works for 2 M to 40M. I have that on a mast up about 20 ft. With it I have contacts in Alaska, Eastern Russia, New Zealand, and Tasmania. Also much of South America. Above that on a short piece of mast I have my home brewed seven element 2M horizontal dipole. Local Hams hear me without rotation on that.
Love your content. Please keep sharing your knowledge! So much good information! I especially like the antenna content because I need help with both height and space for my antennas (small HOA lot). Any new tricks to improve my antenna in my limited space is well received!
Good morning David, I have made both insulated and uninsulated dipoles for 40 and 20 metres. You are quite correct, it does not make any difference if you fold the ends back on themselves. HS0ZQA David Thailand
Interesting. I had a fold back on my 80m extension of my EFHW. It caused the lowest point of the dip in the band to only go down to 2:1. As I trimmed and adjust the foldback the SWR kept dropping till it got down to about 1.2:1. KC3SWZ 73.
Something I learned from DXCommander - when you wrap back a decent amount of insulated wire (say 1-2m extra wire), you actually pull the 3rd harmonic down more than the fundamental, so you can get both 40 and 15 to be perfect. It's worth doing this experiment to see if it works for you too.
Thank you for sharing this interesting and education video with us. I guess the antenna just "catches the wave" and it's the overall length of the antenna (from end to end) that matters and not how much wire (including "wrapbacks") is in the antenna. What would happen if the "wrapback" went all the way along each leg of the dipole so there was in fact twice the amount of wire but the antenna remained the same overall length? Would the antenna receive a stronger signal with twice the wire?
I made a dipole that I cut for 40 into a 20 dipole and I wrapped it all the way back as I didn't want to destroy the 40 metre dipole, and it worked great. David HS0ZQA Thailand
I did the same test with a transformer-fed end fed half wave antenna and noted that folding back seems not to shorten that antenna (much) but cutting it will, as KC3SWZ has observed here also. Maybe it's dependent on how tightly the folded back section becomes capacitively shorted toghether, which depends on how close the wires are and what the insulation material permittivity is. 73, OH3WAV
The foldback of insulated wire result conflicts with some other observations, it has been said that for example if you foldback a significant length of insulated wire the resonant frequency does not go up as high as it would if the wire had been cut. I should try some small scale examples with a VNA ... thank you for the video 73
Good stuff Dave, once again. In my early days of radio I wondered about insulated or non insulated wire and decided there was no difference. Only an SWR meter back then. I also folded wire back with the same conclusion. Wire is cheap. 20 to 10m so five dipoles in my attic but three coax cables to make tuning easier with less interaction. G4GHB.
What about a full-wave circular loop made from small copper tubing on 10 meters using rg-59 coax matching stub, could you electrically shorten it by re-soldering one end progressively to tune, and folding excess inward?
Thanks Dave. I've often wondered about that. Now tell me, would two or more antenna wires of equal length running parallel to each other, only being connected at each end, result in more signal strength into the receiver?
Probably not. However, if the two wires are connected only at the tips of the antenna (and not in the middle), you have constructed a folded dipole. The feedpoint impedance will be considerably higher. To get a predictable folded dipole, you need a constant spread for the whole length of the antenna. There are numerous resources on the Internet and in the ARRL antenna book.
Thanks Dave. Very interesting experiment and results. Would be curious though if the insulated wire wrapped back, if in a tighter coil configuration and greater extended length, might influence the resonant frequency more readily. Not sure if the insulated tighter wire coil would actually shield the signal, add capacitance or simply exhibit parasitic coupling. Obviously, cutting off the extreme excess of wire would be the solution of course, but my response/question is more theoretic in nature and a pondering point. 73, Dave, AC3HT
Groovy! I am going to build a full wave horiz loop about 1.3 waves long at 40m. Then tie another identical loop onto it only connected electrically at far end to first loop and not at feedpoint. Hopefuly forming a widebanded, high impedance twin lead fed radiator that will have low takeoffs at 20 meter with old style manual transmatch. Like turning a folded dipole into a loop, even though a folded dipole is already a loop, hence only one connection in my "Folded Long Loop". No data or modeling predicts the behavior authoritatively, so the only way to find out is to try it. I think it might come out at 600 Ohms or higher and if lucky, being low to ground, could hit near 450 ohms which could be a killer match, or the current directions in the antenna are unpredictable and may be self cancelling....?
Hi Dave, you did a nice experiment. But you made a mistake, which did not change the results, but may confuse some hams. See 6:35! The wire is in direct contact with the rope, the insulator is useless. It might matter during transmitting, if the rope was wet.
I built a Moxon antenna with the wire connected via paracord, tuned up great in the dry weather, and was terrible in the rain. I need to put some insulators on there if we get a sunny day.
The folded back bare copper wire is shorted to the main wire, hence will not make any difference as long as it is wrapped reasonably tightly. 73, Dave, KEØOG
Did not see where you explained the law for capacitance reactance Xc = 1/2Pi * FC. As you wrap a insulated wire back onto itself you are making a capacitor.. Thus RF will see it as one wire in spite of it being two since the RF passes through the capacitor before it reaches the end
If you wrap back a decent amount of insulated wire for tuning you need to leave the excess attached afterward. I wrapped a couple feet of excess insulated wire back on a 75 meter dipole to get the tune I wanted. After getting it all tuned I snipped off the excess. Then my antenna was too short! This shouldn’t be an issue with bare wire since it shorts back onto itself but the insulated wire is still an extended antenna while wrapped back, just not as much as if it were extended all the way outward.
It is tidbits like this that make life so much easier for many of us that have been hesitant when it came time to make that final bit of tuning for fear of destroying an antenna that looks good on paper, but is just that little bit off.
This experiment should encourage everyone to try adjusting their (isolated) wire antennas just by wrapping back the excess wire. The folded back piece of wire, as long as it’s close enough (and it usually is) to the main wire, takes the RF - inductively coupled - with it and doesn’t affect the expected properties much. It works, that’s all we want. Only if you want to get overly precise, you must take the foldback into consideration as a kind of capacity hat, which makes the antenna electrically a little bit longer. The higher your frequency, the more you will notice that effect. Thank you very much for this highly instructive video! Vy73 DB6YC
Hi Dave. I feel I have something to contribute here. It concerns small backyards. When I first got my license I went on 2 meter nets and explained that I had only a 30 x 15 ft backyard. There is also an unhelpful very tall inaccessible spruce tree in the neighboring yard. Declaring this on one of the weekly networks an Elmer showed up. My Elmer suggested an vertical he found on Ebay. It worked somewhat but I noticed that he had an MFJ 1775 rotatable dipole that works for 2 M to 40M. I have that on a mast up about 20 ft. With it I have contacts in Alaska, Eastern Russia, New Zealand, and Tasmania. Also much of South America. Above that on a short piece of mast I have my home brewed seven element 2M horizontal dipole. Local Hams hear me without rotation on that.
Dang, I wish I had watched this two weeks ago, before tuning up my shiny new EFHW.
Good question, and good experiment!
Dave it’s funny we were walking in the French Quarters N.O. and ran across a street musician playing your song 😂
Thanks Dave!! I put my first wire antenna up last month. 80 meter efhw and I’m having fun experimenting
Awesome Dave!! 👍👍👍
Excellent, thank you sir
Love your content. Please keep sharing your knowledge! So much good information! I especially like the antenna content because I need help with both height and space for my antennas (small HOA lot). Any new tricks to improve my antenna in my limited space is well received!
Very informative.
Good morning David,
I have made both insulated and uninsulated dipoles for 40 and 20 metres.
You are quite correct, it does not make any difference if you fold the ends back on themselves.
HS0ZQA David Thailand
informative as usual. Thanks
Interesting. I had a fold back on my 80m extension of my EFHW. It caused the lowest point of the dip in the band to only go down to 2:1. As I trimmed and adjust the foldback the SWR kept dropping till it got down to about 1.2:1. KC3SWZ 73.
Something I learned from DXCommander - when you wrap back a decent amount of insulated wire (say 1-2m extra wire), you actually pull the 3rd harmonic down more than the fundamental, so you can get both 40 and 15 to be perfect. It's worth doing this experiment to see if it works for you too.
Thank you, again, Dave. Grazie. N0QFT
Thank you for sharing this interesting and education video with us. I guess the antenna just "catches the wave" and it's the overall length of the antenna (from end to end) that matters and not how much wire (including "wrapbacks") is in the antenna. What would happen if the "wrapback" went all the way along each leg of the dipole so there was in fact twice the amount of wire but the antenna remained the same overall length? Would the antenna receive a stronger signal with twice the wire?
I made a dipole that I cut for 40 into a 20 dipole and I wrapped it all the way back as I didn't want to destroy the 40 metre dipole, and it worked great.
David
HS0ZQA Thailand
I did the same test with a transformer-fed end fed half wave antenna and noted that folding back seems not to shorten that antenna (much) but cutting it will, as KC3SWZ has observed here also. Maybe it's dependent on how tightly the folded back section becomes capacitively shorted toghether, which depends on how close the wires are and what the insulation material permittivity is. 73, OH3WAV
The foldback of insulated wire result conflicts with some other observations, it has been said that for example if you foldback a significant length of insulated wire the resonant frequency does not go up as high as it would if the wire had been cut. I should try some small scale examples with a VNA ... thank you for the video 73
Good stuff Dave, once again.
In my early days of radio I wondered about insulated or non insulated wire and decided there was no difference. Only an SWR meter back then.
I also folded wire back with the same conclusion.
Wire is cheap. 20 to 10m so five dipoles in my attic but three coax cables to make tuning easier with less interaction.
G4GHB.
What about a full-wave circular loop made from small copper tubing on 10 meters using rg-59 coax matching stub, could you electrically shorten it by re-soldering one end progressively to tune,
and folding excess inward?
Thanks Dave. I've often wondered about that. Now tell me, would two or more antenna wires of equal length running parallel to each other, only being connected at each end, result in more signal strength into the receiver?
Probably not. However, if the two wires are connected only at the tips of the antenna (and not in the middle), you have constructed a folded dipole. The feedpoint impedance will be considerably higher. To get a predictable folded dipole, you need a constant spread for the whole length of the antenna. There are numerous resources on the Internet and in the ARRL antenna book.
Thanks Dave.
Thanks Dave. Very interesting experiment and results. Would be curious though if the insulated wire wrapped back, if in a tighter coil configuration and greater extended length, might influence the resonant frequency more readily. Not sure if the insulated tighter wire coil would actually shield the signal, add capacitance or simply exhibit parasitic coupling.
Obviously, cutting off the extreme excess of wire would be the solution of course, but my response/question is more theoretic in nature and a pondering point.
73, Dave, AC3HT
Hi Dave, I don't think it would make much difference. 73, Dave, KEØOG
Groovy! I am going to build a full wave horiz loop about 1.3 waves long at 40m. Then tie another identical loop onto it only connected electrically at far end to first loop and not at feedpoint. Hopefuly forming a widebanded, high impedance twin lead fed radiator that will have low takeoffs at 20 meter with old style manual transmatch. Like turning a folded dipole into a loop, even though a folded dipole is already a loop, hence only one connection in my "Folded Long Loop". No data or modeling predicts the behavior authoritatively, so the only way to find out is to try it. I think it might come out at 600 Ohms or higher and if lucky, being low to ground, could hit near 450 ohms which could be a killer match, or the current directions in the antenna are unpredictable and may be self cancelling....?
Hi Dave, you did a nice experiment. But you made a mistake, which did not change the results, but may confuse some hams. See 6:35! The wire is in direct contact with the rope, the insulator is useless. It might matter during transmitting, if the rope was wet.
I built a Moxon antenna with the wire connected via paracord, tuned up great in the dry weather, and was terrible in the rain. I need to put some insulators on there if we get a sunny day.
Okay for a test in dry weather as you say
G4GHB.
Good point
Where is comparison between bare copoer wire dipole with ends folded back vs ends trimmed up ? I didnt see that in video ?
The folded back bare copper wire is shorted to the main wire, hence will not make any difference as long as it is wrapped reasonably tightly. 73, Dave, KEØOG
Did not see where you explained the law for capacitance reactance Xc = 1/2Pi * FC. As you wrap a insulated wire back onto itself you are making a capacitor.. Thus RF will see it as one wire in spite of it being two since the RF passes through the capacitor before it reaches the end
👍👍
If you wrap back a decent amount of insulated wire for tuning you need to leave the excess attached afterward. I wrapped a couple feet of excess insulated wire back on a 75 meter dipole to get the tune I wanted. After getting it all tuned I snipped off the excess. Then my antenna was too short! This shouldn’t be an issue with bare wire since it shorts back onto itself but the insulated wire is still an extended antenna while wrapped back, just not as much as if it were extended all the way outward.