Homemade EFHWA Antenna ideas?

[darklife]

End Fed Half Wave Antenna

I built a simple 8:1 balun out of a ferrite rod to feed the end of a half wave resonate wire and it works fantastic as far as I can tell.
The secondary coil has the ground riding side open and needs nothing extra to excite the hot side going to the end fed wire in almost all situations because of natural capacitance in the ferrite coil windings.
SWR is down below 1.3 on average, and when it gets cranky I just move the wire around a bit and it drops to where it should be depending on positioning and surrounding objects.

One of the best parts of this antenna in my experience is that the wire end you can arrange in almost any configuration. You can do vertical, horizontal, half vertical and horizontal for L configurations of almost any type, even square or 1/3 square configs an they all seem to get out far better than the best whip antennas on a metal surface I have tried, or even the 102" whip.
They can be tossed up into trees with an egg insulator between for camping, and they can be draped out of buildings windows when high up in the air.

I wonder how many people here have played with this antenna design on 11 meters?
It seems to be an oddball antenna in that there is not much info out there on how to build one (mostly the transformer section) but those who use them swear by them.
Also you get the joy of erecting a vertical dipole without the stress in the center from coax, or the annoyance on how to run the coax sideways enough to make the whole stupid thing vertical.

In theory the EFHWA antenna is a lot like a j-pole. Main difference is the impedance transformer is done via a coil around a torroid or ferrite bar instead of through the U tuning section of a physical j-pole.
Also the use of a coil decouples the antenna from the feedline further reducing troubles.
Best of all there is only one wire at the end so cutting and trimming to resonance is a piece of cake unlike the slim-jim or j-pole.

I will have to post pictures of my EFHWA box tube shaped thingy I made to connect a 1/2 wave wire to.

Thanks for any further ideas or tips in the meantime!

Excellent page I learned a lot from to design your own...
AA5TB - The End Fed Half Wave Antenna

 

[vkrules]

Always good to see someone building their own antenna . For single band use what are the advantages of building this type over say a T2lt or a bazooka ?,both have the coax out the end and are cheaper and easier to make.The only advantage I can see is that the 8:1 balun makes it easier to use on other bands just by changing the wire length.Or alternately you could make the wire 32 ft and get a few bands out of it.

 

[hobie102]

Thanks for sharing this. I would love to see detailed pictures of your build as I am a visual person when you get a chance. Love building things. Although the science behind this antenna is way over my head it's still interesting. Thanks again. op:

 

[2RT307]

I have one that HomerBB built. It works very well on 11 and 10 meters (I have to change the jumper to adjust the SWR). It has a coil and a slide bar assembly for tuning. I really don't know *how* it works, but know that it does a good job. Mine is only hanging up about 8 feet in the air horizontally, but I can still talk DX with it. Work decent locally even in this fashion.

73,
Brett

 

[W5LZ]

No matter what the length, all of those end fed wires are more or less a compromise. They all require a very good ground system to 'work against'. Sometimes that 'ground system', counterpoise, whatever, is the feed line feeding the thing, but the 'other half' is always there. They are typically a modified shape vertical antenna. If it satisfies your requirements then it's a good antenna.
I've always had a problem that that sort of antenna. (Too @#$ lazy to put in a good ground radial system.) There's a world of difference with/without that radial system, you have to experience it to know.
- 'Doc

 

[darklife]

Hello again. Got some pictures this time.
I made a mistake, it is not a 8:1 ratio but a 9:1 for the transformer. The idea is to convert from a current feed to a voltage feed since a dipole at the end requires voltage compared to a center fed dipole where you feed it current.

Ground radials are NOT needed in most cases and any stray RF going back down the coax can be cleaned up with a current balun (1/4 wavelength length of coax around a PVC pipe) or quite a few torroids on the outside of the coax.
This is identical to the j-pole in how it interacts with stray common mode currents running along the coax and can be cleaned up accordingly.
I have used this with great success without any need to choke it off down the coax but in some setups I am sure you would want to, especially when using higher power levels.

Ferrite bar from AM broadcast band radio used. Wire diameter size unknown but most online plans can point out what sizes to use and so on.
Wire to the far left is antenna connection, the other wire is used for a short ground stub wire if needed.

Put into a pill container for portability. Probably will put it in something more permanent in the future.

Normally there would be a tuning capacitor in parallel with the secondary coil to tune the LC to resonance. I somehow managed to get the amount of wire and spacing just right on the spot so I did not need the trimmer capacitor commonly found in these designs.

I have no idea how much power this could handle. With stock power (4 watts) there is no noticable heat from the ferrite bar so I would assume it can handle a few tens of watts before failure.
Ferrite bars are very wideband but can not handle a lot of heat so for the higher power levels a torroid would be more appropriate.

This has only been tested on the CB. I do not know how well it would work outside of this range or if some of the values would need to be changed to make it work. I only plan on using it for CB anyways

 

[darklife]

For single band use what are the advantages of building this type over say a T2lt or a bazooka ?,both have the coax out the end and are cheaper and easier to make.The only advantage I can see is that the 8:1 balun makes it easier to use on other bands just by changing the wire length.Or alternately you could make the wire 32 ft and get a few bands out of it.

There is no advantage as far as gain goes. A dipole is a dipole and thus the EFHWA will have no additional gain over a bazooka for example.
One of the advantages is decoupling the antenna from the coax which greatly reduces common mode currents returning down the line.
Also as you said it can be made to work multiple bands easily by just changing the wire length on the end, or as you said go with 32ft to work a lower band plus the CB band.
I think it may be possible to add multiple lenghts of wire to the transformer connector to work more than one band also like a multi-band dipole.
BTW this was rather easy to make by following the basic instructions on the website I linked.

 

[W5LZ]

An end fed 1/2 wave antenna will perform just like a center fed 1/2 wave antenna, the only difference is in how it's fed. An end fed antenna can be more convenient in some circumstances. Because of the very high impedance when it's end fed, there's some losses associated with it, not much, but some. And because of how you 'string it up', there can be some differences in it's radiation pattern.
As for using it on multiple bands, it's not going to do any better than a center fed 1/2 wave. That balun isn't going to make any difference in that regard, it will still be a compromise because of impedance mismatch, no 'magic bullet', no 'cure-all'.
If it serves you particular purpose then by all means use it!
- 'Doc

 

[darklife]

That balun isn't going to make any difference in that regard, it will still be a compromise because of impedance mismatch, no 'magic bullet', no 'cure-all'.
If it serves you particular purpose then by all means use it!
- 'Doc

Well technically even a standard dipole imposes an impedance mismatch since it looks like a 70ohm load into a 50ohm coax depending on antenna height above ground, then to make matters worse one is going from an unbalanced coax to a balanced antenna which introduces its own set of problems.

I bet the best way to avoid that would be to go with twin lead/ladder line for the feed line into a folded dipole or something similar where there is little loss and then have a balun along the line somewhere to convert back to coax to the radio, but of course that is far out of the scope of this thread

As you said it does serve my purpose and seems to work excellent.
I like the fact that it makes a nice easy to toss up or take down portable 1/2 wave antenna that can be strung vertically without trouble.
I have always had good luck with j-pole antennas and this being basically the same idea does not surprise me that I also have success with this.

Thanks for the replies so far.