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End Fed Antennas

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I'm doing a little reading on HF antennas in preparation for getting my hf station up and running. The end fed geometry is particularly convenient for my property layout.

In looking over the end fed zep, it strikes me as an HF J-pole. Am I wrong?
 
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As with any end fed antenna you are going to require a good RF ground. Hopefully you can drive one or more ground rods into the soil.
 
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You need a good ground for several reasons but the short answer is that an end fed antenna is inherently unbalanced. This is because unlike a dipole, the "system" is asymetrical. In a truly balanced system, there would be negligable RF ground current flowing. Do not forget that in an end fed system, the feedline will radiate RF energy. You use a tuner to make the end of the feedline "look" like a proper load to the transmitter, this does nothing for the SWR on the feedline.
I am assuming that you would be feeding it with open wire line to minimize losses so coiling the feed line is probably not a good thing. If however, you are using a coax feedline, a choke will keep the coax from radiating but not help the efficiency at all. A proper RF ground will definately improve the efficiency of an end fed system.
HTH
 
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You need a good ground for several reasons but the short answer is that an end fed antenna is inherently unbalanced. This is because unlike a dipole, the "system" is asymetrical. In a truly balanced system, there would be negligable RF ground current flowing. Do not forget that in an end fed system, the feedline will radiate RF energy. You use a tuner to make the end of the feedline "look" like a proper load to the transmitter, this does nothing for the SWR on the feedline.
I am assuming that you would be feeding it with open wire line to minimize losses so coiling the feed line is probably not a good thing. If however, you are using a coax feedline, a choke will keep the coax from radiating but not help the efficiency at all. A proper RF ground will definately improve the efficiency of an end fed system.
HTH

well, at 30MHz and below coax line losses are quite small, so no - I would probably would not feed with a balanced line for the purposes of limiting loss.

In reading a bit more, there seems to be a fair bit of contention between two well entrenched groups on the issue (can you believe that? on the internet? who'd a thunk it?). The fact that there is an issue with feedline radiation leads me lean toward your understanding. In an old issue of qst there is an article on an HF Jpole where they do pin the base of the J to ground and this makes sense for diverting those currents to ground and preventing feedline issues, but it's not clear to me why that makes it more efficient. Doesn't the energy just go into the ground instead of being eaten up in/poorly radiate from the feedline?

I really need to pick up the antenna reference from ARRL I think.
 
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well, at 30MHz and below coax line losses are quite small, so no - I would probably would not feed with a balanced line for the purposes of limiting loss.

In reading a bit more, there seems to be a fair bit of contention between two well entrenched groups on the issue (can you believe that? on the internet? who'd a thunk it?). The fact that there is an issue with feedline radiation leads me lean toward your understanding. In an old issue of qst there is an article on an HF Jpole where they do pin the base of the J to ground and this makes sense for diverting those currents to ground and preventing feedline issues, but it's not clear to me why that makes it more efficient. Doesn't the energy just go into the ground instead of being eaten up in/poorly radiate from the feedline?

I really need to pick up the antenna reference from ARRL I think.


I believe he's talking about SWR-related losses. In a multi-band ham antenna, you'll be seeing all kinds of SWR levels at the feedpoint depending on what band you're operating on. Coax has very large line losses due to SWR compared to open wire.

Here's a clipping from the ARRL Handbook showing the SWR losses for coax and open wire for a 100 foot antenna.

handbook%20clipping.jpg


On the second question, I believe the bigger issue with not having a good RF ground is that your take-off angle will be severely compromised with no return reference, and your antenna will radiate strait up, NVIS style, but I'm going to have to do some reviewing on this.
 
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well, at 30MHz and below coax line losses are quite small

Until you try to load that end fed 40m zep on 80m and vswr goes to 1:100. If you try using a tuner the rig sees a good load but you still have a mismatch on the feed line and lots of common mode current on the braid. The noise floor goes way up also. I feel the best way to use a end fed antenna is with a good rf ground and different lengths of ladder line for each band.
 
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On the second question, I believe the bigger issue with not having a good RF ground is that your take-off angle will be severely compromised with no return reference, and your antenna will radiate strait up, NVIS style, but I'm going to have to do some reviewing on this.
You beat me to it:) I also believe you will have pattern problems with the secondary lobes as well as the takeoff angle increasing. If I had nec on this computer I would model it but I am a little to lazy for that. The Antenna book is the best one put out by arrl imo.
 
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Mark and Eric are both right. when I was referring to feedline losses, I was talking about losses from high VSWR in coax. Marks chart tells the story. Also look at some of the voltages that are produced with high SWR. Depending on the frequency and the lengths involved, you might have that kind of RF voltage inside the shack. A ground will help to mitigate the issues created with RF in the shack. Dont forget that near resonance, the dipole is current fed however, the end fed is voltage fed. With an end fed antenna off resonance, the feedline is going to radiate RF due to system unbalance. Depending on the frequency and the lengths you have chosen, you will have a varying impedance (and SWR) on the other side of the tuner (feedline side).

Another reason to have a good ground is for lightning protection. A lightning bolt does not have to hit your antenna to do damage. A neerby hit can induce very high voltages in an antenna that can cause damamge to your equipment. A good ground together with either a grounding switch or some other form of protection will keep your gear happy.
 
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Until you try to load that end fed 40m zep on 80m and vswr goes to 1:100. If you try using a tuner the rig sees a good load but you still have a mismatch on the feed line and lots of common mode current on the braid. The noise floor goes way up also. I feel the best way to use a end fed antenna is with a good rf ground and different lengths of ladder line for each band.

I'm trying to find the post, but someone on QRZ came up with a multiband setup that's essentially switched length open wire fed 1/2 wave, I think. The switching mechanics were quite impressive.
 
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With an end fed antenna off resonance, the feedline is going to radiate RF due to system unbalance. Depending on the frequency and the lengths you have chosen, you will have a varying impedance (and SWR) on the other side of the tuner (feedline side).

Another reason to have a good ground is for lightning protection. A lightning bolt does not have to hit your antenna to do damage. A neerby hit can induce very high voltages in an antenna that can cause damamge to your equipment. A good ground together with either a grounding switch or some other form of protection will keep your gear happy.

Exactly! Kirchhoff is a law for a reason. There has to be a counterpoise someplace, with out one the feed line becomes one. Imo there needs to be a lc circuit at the feed point. A end fed zepp has a impedance of about 1800 ohms. w8ij and aa5bt have good info about end fed zepp's.
As far as lightning protection Polyphaser has a very good pdf document about it.

I'm trying to find the post, but someone on QRZ came up with a multiband setup that's essentially switched length open wire fed 1/2 wave, I think. The switching mechanics were quite impressive.
I used knife switches to switch different lengths of ladder line in and out to tune the feed line to the antenna feed point impedance. The post on qrz you referenced used info from ??? I can't remember who but I found him on dxzone I think. It worked quite well but my setup was very Rube Goldberg and I tore it down in the interest of safety.
You know I just have to add that I can't stand people who tune up on frequency! I am listening to jy5cc now and it pisses me off.
 
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That's the one. It works well. If you work lots of qrp it should really help maximize your erp.

The problem I'd have here is feed line management. The stub on my W5GI would almost touch the ground if it wasn't secured, and that's about 34 feet. This design calls for a 90 foot section from the feedpoint to the "tuner", so I'd have to figure out how to manage about 56 feet of free ladder line.
 
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The problem I'd have here is feed line management. The stub on my W5GI would almost touch the ground if it wasn't secured, and that's about 34 feet. This design calls for a 90 foot section from the feedpoint to the "tuner", so I'd have to figure out how to manage about 56 feet of free ladder line.

Wrap it around a 5 gallon plastic bucket. Dont let the wraps cross.
 
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I might have to try it this summer. Still, 56 feet is alot of ladder line around that bucket. I'm thinking big, big inductor.

Not really, that bucket is 36 inches in circumference so 56 feet would be about 18 turns. The inductance should be negligable because the ladder line carries equal and opposite currents (sort of) and they will cancel to some degree. Also the diameter is huge so the inductance should be small.
 
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Not really, that bucket is 36 inches in circumference so 56 feet would be about 18 turns. The inductance should be negligable because the ladder line carries equal and opposite currents (sort of) and they will cancel to some degree. Also the diameter is huge so the inductance should be small.

I just may have to try this just to see. The house is going to look weird with a 5 gallon bucket stuck to the side with ladder line wrapped around it though!
 
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