Magic 80m band

From 4NEC of an inverted V, 80m,20m bands,
Efficiency % and Radiation efficiency%

1.0mm Cu 80m = 95% , 66%
0.5 Cu 80m= 90% ;20m = 93%, 71%
0.2 Cu 80m = 75% , 56% ; 20m=85%, 64%
0.2 Stainless Steel, 10%, 8%
(6x0.25 ~=0.5mm round, ~1mm if flat)
While slightly counter intuitive, loss is directly proportional to length, but skin effect is sqrt of freq. So higher freq makes dipole more efficient.

As long as you have plain copper or silver plated copper, any practical thickness of wire is OK.

If you have tinned copper, galv, or stainless then it shouldn’t be very thin.

It’s even more wrong as the wire is Litz wire and not single strand.

It is not Litz, It looks perhaps to be flat stranded, like a ribbon form wound on the core. (which would be better loss than a circular bundle. Area~=7D for hex bundle vs ~13D for flat bundle)

What is important about Litz (braided, insulated) wire is that whereas a bundle of enough strands in a normal twisted wire would have an inner bundle that is always inside,
in true (braided) Litz, all the strands get to spend some time on the outside.
A bundle of twisted (unbraided) insulated strands is not Litz, and has excess loss as the magnetic fields affect current in the inner strands relative to the outer strands.

If you do that, then when a strand breaks, it is totally lost to the whole antenna. (but perhaps still contributes some eddy current losses). In a conductive bundle a break is only a tiny increase in R, as it is soon reconnected back to the other strands. [debate topic: does capacitance reconnect it?]

The lovely antenna wire below (stripped) is braided, but I think the reason is to keep it more flexible, as it is made from hard drawn copper.

I presume its because of proximity effect. Using litz wire for rf you have to consider both skin effect and proximity effect.
It’s similar to (radio-frequency) litz wire.

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No they are not. Wanted a big spool to play with a 3/8th wave on 160m and they will only sell for orders over £130 UKP due to customs difficulties.

PS I use the wire for a 40m loop and a 160m doublet between trees - so far so good and it is small enough not to be too visible.

If the value of your order will be under £39 then asking a friend who lives in the EU to order it and then send it to you as gift is a way around the VAT changes. They will pay their VAT and p&p to get it delivered to them. Then you pay them what they spent plus p&p to the UK (Paypal Friends and Family so there are no charges) and they post it to you with a gift customs label. Gifts up to £39 are free of import VAT and duty so ordering it this way is not defrauding any of the UK/EU tax authorities. But you do need a friend to get involved etc. and it’s a pain.

Or you get several people in the UK to do a pool order which will be over £130 and then get one order shipped to the UK with VAT charged on entry plus admin fee. (£8-£12 if just using the post service not a courier) and then split up the order and ship to individuals. Which is also a pain.

Sadly it’s the one of the costs of leaving the single market and its advantages of frictionless trade although there are big changes to VAT coming to the remaining 27 EU states on July 1st. However, that deal is done now and there’s no real possibility of the UK rejoining in my lifetime so we have to make the best of a bad deal when importing small orders now.

The strands are un-insulated, and so I think they can be considered like a single conductor i.e the current is forced out to the surface by skin effect.
Only when the strands are insulated can you force current through the inner strands, and thus get proximity effects between adjacent strands.
Unless the effect of braiding stiff wire is to create some partial air gap insulation of the strands.(see photo)
I’m still thinking flexibility. It’s a bugger to strip, so holding the plastic really well is another effect.

BTW true (braided) litz is only needed for straight antenna wires in MF loop antennas where radiation R is very low, and the litz strands are workable thinness. (At 80m you are needing something like 25um or 40um strands from memory.)
For coils, non-braided twisted insulated bundles work, and this is what is often misnamed Litz. The replacement induction stove element in front of me uses that.


Does that have an approximate effective diameter as a single piece of wire the same size and so a skin depth of the single wire? Or is there some increase in skin depth due to the braiding? And yes, it probably is braided for mechanical reasons.

In 1994 I replaced my 2m Yagi with a Tonna 17ele and masthead preamp. The preamp was bought from another ham used and I spent a few weeks in the shack in circuit to check everything was working correctly. Up it went and the bigger antenna and masthead preamp was obviously better than before. Within a few days the preamp failed. It wasn’t possible to recover it for some time and during that RX was fine as was TX. When recovered the relays had stuck and the TX signal had been back fed into the GAsFET drain and out through the gate to the antenna. Measuring the FET showed open circuit between all 4 pins, not surprising as it had 150-200W of 2m fed through it. Whilst it was OC, the remaining capacitance between across the device was enough for RF to flow both ways unimpeded. Regular 2m contacts reported no obvious change in my TX strength after the preamp was replaced with an N to N adapter. The preamp was repaired and used in a contest station for some years after that.

To get back to the topic of the thread.

Today after my CW call I heard Andy UW8SM on 80m. I didn’t trust my ears and my brain and thought it was impossible that a UW station 1000km away could hear me. So I didn’t came back.

Luckily Andy kept calling and finally we finished the qso. Thanks Andy for your persistence.

Magic 80m band!

73 Chris

Andy send me a email: "My RX antenna is 300m long beverage to 310 deg.
I never heard you before on 80m. It was a very big surprise for me! "
Now I will listen carefully for his call.

73 Chris

Hi Chris,
Tnx for many Sota contacts. Why not try an extension of your EFHW to be 40 m long instead, as you are a regular customer on 80 m?
73 / Lars

Lars, yes, you a right When I started my first sota activities on 80m I use a 40m long wire on my 1:49 unun for a true HW. The next time I put it in my backpack. Maybe you come back with your new key :grimacing:
73 Chris

One link that takes care of 60/30 m perhaps?.

At the moment I only want to spot on 80m. My CW knowledge is still very limited and I get into great unrest when I hear several callers. In the nervousness I don’t understand and I can’t key anymore.
Unfortunately, I am not very calm.
On the other hand, I can be happy like a little boy when a connection that is unfamiliar to me works.

73 Chris

As a compromised, but shorter radiator solution, you could also add a coil of about 110uH at the end of the 20m long wire. After the coil, about 2.5m wire should suffice so only 22.5m long in total.


The advantage of adding the coil would be a better radiation diagram for the 40m band and up, compared to the 40m wire, albeit less efficient on the 80m band. But still no tuner needed if the antenna is high enough. For 80m you need at least a 1:64 transformer and enough primary inductance, definitely more than for 40m and up.

I tested this setup and similar ones for the 80m band (and extended it to 160m) mainly in an inverted-L configuration, but inverted-V and other configurations should work as well.

73 Stephan


EFHW bobine 80m


Hello Chris. I feel the same way. I’m currently also trying more CW in SOTA activations and rather try bands that are not so busy. I always find it exciting how experienced CW ops manage the calls. Maybe one day we will become a bit more experienced too :wink:

73 Marcel DM3FAM


You will for sure. Just keep working CW and the magic of your plastic brain will make it happen.




Last ThursdayI compared the 40m HW with my 20m long QW. At the rx of our remote station 40km away, my signal was approx. 1 to 2 S steps louder.
Unfortunately the conditions on 80m were bad that day. Lars, SA4BLM hardly heard me. But Bill, G4WSB gave me 33 and I gave him 44. So the test was still a success.

73 Chris