Question on inductance

More learning curve here

Been looking up inductance and worked out by coiling me vertical antenna that 10% off the mark 1/4w 40m LOL yep random wire with idea of nearness to 1/4w . But looked at the coiling effect by using a cal that shows dia of the pipe am using length and how many coils. And it shows if pipe was smaller or more coils on me pipe the inductance increases in uH from what i can see.

Now question is if greater amount of uH ( think got that right) is introduced like it did when first did it by making me coils next to each other so they touch and found 40m would not tune in by any means But by spacing them out by at least 1cm apart its less inductance and can tune in 40m and 80m no problem right up to 10m…

Now idea of coiling some of the 11m wire (3m) i use is to loose some of it on way up but keep the over all length of the wire in a little smaller space.

Also by reducing length of me wire over all down to 10.2m and try tune into 7.1mhz better. how much increase would i get out and in. And yes the antenna does tune in at present on all bands i can use of HF down far as 80m. Be nice if i could make the antenna more better. better still would love one of those fancy gadgets. Or how big re these losses am prob encoring.

PS don’t forget one is not to high up doing the maths stuff

Some more experimenting required i thinks


Dr OM Karl,

Maybe this calculator helps?

73 de geert pa7zee

I would forget trying to load your random piece of wire over multiple bands Karl, your going to waste your precious 10W in what will ultimately end up being converted into heat.

With antennas I will always try to avoid loading any element in favor of either changing its length mechanically. Or failing that electrically as close to the transition impedance of which it changes. That ensures low loss in your feed to the radiating element - the purpose of a transmitting antenna.

From the images you have posted of your back yard you should be able to put up multiple antennas.

Why not try a fan dipole OR a loop ?

Simple to construct, good on receive as well as transmit and hardly if any shack based tuning required. Feed it with coax.

Being a keen chaser you should be trying to add ‘diversity’ to your antenna configuration allowing you to find the optimal configuration for chasing a particular SOTA station.

The basic rule of more wire in the sky and as high as you can get it is not a bad starting point.

Hope that makes you rethink things!


1 Like

Hi Karl,

Your antenna is already lower in natural resonance than 7 MHz. Adding a loading coil cannot bring it back UP to 7 MHz, it will take the resonance lower. Adjusting the shape of the loading coil will only change the resulting resonant frequency.

If your coil was self resonant on say 14.1 MHz, then placing the coil at 5.03m height may give you a trap effect where the coil acts as a trap on 14 MHz. But a more efficient way to have multiple resonance would be to add radiators in parallel.

As others have said, using your 11m pole to support a fan dipole would possibly give you improved coverage and better bandwidth with instant band change. I think that would be a pretty good antenna, with dipoles for say 80, 40, 20 and 10m in parallel. Decide which bands you want to use and adjust your plans to suit. Use designs from the standard handbooks (RSGB and ARRL) rather than arbitrarily adding components like loading coils and ATUs.

Experiment are fun but starting with a known good design is likely to give your better results sooner.

Good luck

73 Andrew VK1DA/VK2UH


One of the many articles on horizontal loops should you wish to move in that direction. Multi band, simple to set up and quite effective, particulary on the lower bands.

I work a lot of dx on 40/30M with mine which is 55mtrs of wire suspended on poles and fed with 450 ohm ladder line.

4:1 balun to feed the ladder line.

Homemade open wire feed lines work well.

Good luck with whatever you do, Nick

Thank you that is wicked

Even takes into account size of the wire

At moment its about 18.33 uH

Now if i cut it down to 10:56m length wire from 11m to 10.56m me antenna wire will be more of a 1/4w than before on 40m and the the Uh falls by from 18.33uH to 16.9uH because I have taken off 3 coils off me plastic pipe and keep it same length and it spaces them out a bit more and should bring down me low SWR point more into the 40m band instead of 42mb or even 43mb.

Hmm experiment time

Thanks for that Geert that really is usefull have saved it on me PC for future reference as when doing me reduced size Moxon tells me make sure coils are same number on each side as will introduce a slight difference on the uH and possible un balance the Moxon Di pole part of it.

Right better read rest of the mails attached to this .

Thanks again


Hi folks, thanks for all the input.

Whole idea of me coil is not to load it but to take a length of the antenna wire and and wrap it around it so it shortens the over all length of the antenna down into a 8m length of squid pole instead of the currant 11m and keep the wires spaced apart as closer they are together the bigger the uH. And seems to me the bigger the uH the less likely you are going to tune in the lower part of the band. As I found out tightly and next to each other I found out as that uH measurement is 23uh enough to effect the antenna tuning in of.

Fan DP lovely idea but means more wires about place as i like to use all bands 80m through to 10m hence the one simple antenna 9:1 unun and MFJ and to have a multi fan at home, no can do hence why i have the loop up as i do to not too many antennas up at home and out on site keeping it very simple…

End of day my portable antenna won’t be as effective as a good straight fed tuned wire My home brew does work well and am happy with it even with ten watts. But end of day depending what ionosphere conditions is happening dictates where i can reach hence being an ionospheric jockey.

But now must 1/4w the portable a bit better tuning required then do me 1/2 version.

All good fun messing with antennas and trying to get best out of them.

Big thanks to all again