Temporarily shortening an end-fed half wave wire antenna

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DataSquid

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Hi,

I've been hunting around for anecdotes of temporarily shortening the radiator of an EFHW and using the excess to form an RF choke, but other than one reference to coiling up a bit of extra for adjustment [1] I haven't found much.

I've got an EFHW cut for 80m. Specifically, the EF-QUAD EndFedz Antenna. I anticipate situations where I won't be able to string up the entire length. If I were to coil up the "excess" beyond, say, the 10m half-wave length (maybe even snap a ferrite core around it), what sort of performance/side-effects could I expect?

[1] AA5TB - How to Make An End Fed Half Wave Antenna Work

Thanks.
 

prcguy

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The stock EF Quad by LNR is a 40 through 10m antenna and I'm not sure that transformer will work very well on 80m. Did you lengthen it for 80m?

For 40 through 10m operation on an 80m version you could simply fold the wire in half, double it back towards the transformer and keep it close together. That should give you the 40 through 10m operation and I've done similar things with good results. Not sure if you can fold it at about 16ft long and have it work as a 10m only without all the extra wire having some negative effect but its worth a try.

Why not just have a couple of shorter tuned lengths to swap out when you don't need the full 80m length? A friend of mine did this just the other day taking a 40m version I made for him and swapping out the wire with a 17m specific length and it works fantastic.
prcguy


Hi,

I've been hunting around for anecdotes of temporarily shortening the radiator of an EFHW and using the excess to form an RF choke, but other than one reference to coiling up a bit of extra for adjustment [1] I haven't found much.

I've got an EFHW cut for 80m. Specifically, the EF-QUAD EndFedz Antenna. I anticipate situations where I won't be able to string up the entire length. If I were to coil up the "excess" beyond, say, the 10m half-wave length (maybe even snap a ferrite core around it), what sort of performance/side-effects could I expect?

[1] AA5TB - How to Make An End Fed Half Wave Antenna Work

Thanks.
 

DataSquid

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Oops, posting too soon after too much pie. Yes, it's the stock 40-20-15-10.

It's a bit of being optimistic, a bit of having to pack light. I plan to/hope to run the full length, and I'm not able to bring any other radiators/spare wire, so I want to have a plan for if I don't have space available. I had considered doubling-back, but I had thought it might be more finicky to tackle, as it's probably important to keep the wires tight together, and while twisting them is an option, I'm not sure what that would do emissions-wise.
 

RFBOSS

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My traveling EFHW antenna is 100 ft long steel tape measure.

Easy peasy...

I pull out the length that I want for the band that I want to operate on.

Any hey, when I am finished, I just wind up the tape measure.

I just checked on the net and they are still available and listed shipping weight is 2.85 pounds.
 

prcguy

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My portable EFHWs are mostly used in the daytime, so I don't need 80m. For a 100w 40/20/15/10m version I can fit 63ft of 22ga Teflon wire and 40ft of miniature parachute cord inside a plastic chalk line reel that weighs 8oz full up.

The 64:1 transformer fits in a box about the size of a Zippo lighter and the antenna spools out and is on the air in a minute. The chalk line reel makes a great throw weight to get the antenna up in trees and the geared crank handle makes teardown go faster than putting the antenna up.

If I had to carry an additional length of wire for an odd band it would only weigh a few grams and take up virtually no space.
prcguy

My traveling EFHW antenna is 100 ft long steel tape measure.

Easy peasy...

I pull out the length that I want for the band that I want to operate on.

Any hey, when I am finished, I just wind up the tape measure.

I just checked on the net and they are still available and listed shipping weight is 2.85 pounds.
 

TheSpaceMann

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Apr 3, 2014
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1,333
My traveling EFHW antenna is 100 ft long steel tape measure.

Easy peasy...

I pull out the length that I want for the band that I want to operate on.

Any hey, when I am finished, I just wind up the tape measure.

I just checked on the net and they are still available and listed shipping weight is 2.85 pounds.
Interesting! Who makes that antenna? :)
 

RFBOSS

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Lufkin

Stanley

Keson

And others.

And if you use two you can make a dipole antenna.

Again, this is just something that can be done and there may be those that find fault with it, but I have used this method and it has worked well for me. It is by no means the only way.

I used a little extra wire on the end for 75 meter operation.

BTW, it is not like I have not used just a basic roll of wire fine gauge wire for size and weight considerations, but for the traveling and portable operation that I have found this to be easy and the size and weight are not a burden. The one I mentioned in my first post was a heavy duty contractor grade unit, but the cheaper consumer grade ones are much smaller and lighter.

The one I have in my current go pack is a light weight consumer version that weighs I would guess less than 12 ounces.

A couple of advantages that I have found with this.

The length is right on the tape measure. It is rugged and it does not kink or break. When I change bands all I do is turn the crank.

And when the wife (before I lost her and she was also an amateur radio operator) and I would camp in the back woods, sometimes a tape measure would come in handy. Who would think, using an antenna for a tape measure...ha ha

The blade of the tape measure is day glow orange. Helps to keep people (sometimes even me) and birds from bumping into it. Of course if you need stealth, that is another story.
 

mancow

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How does the orange paint/insulation or whatever coating of the tape not insulate the material and form a coil that affects resonance? That's something I always wondered about these. I might have to go out and try to find one tomorrow. It sounds really handy.
 
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