End-Fed Half-Wave Dipole Orientation?

WeldGuy

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I'm planning the location of my end-fed, half-wave dipole antenna. I have two open locations from my tower. I will feed it from 25 feet up.
Choice One: From the tower, NORTH to an attaching point about 20 feet up.
Choice Two: From the tower, WEST above (along) the peak of the roof of the house.

Being located in Central Ohio, is there much difference in performance NORTH-SOUTH vs EAST WEST?
Will the proximity to the ridge of the roof affect the performance significantly?

Your wisdom is always appreciated.
 

popnokick

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Assuming no obstructions in the north direction from the tower, it will work best AWAY from the house. The closer to the house the more potential to pick up RFI / EMI noise from devices in the house. Getting it away from the house will reduce the noise floor in your radio.
 

prcguy

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Is it a 40m and up or an 80m and up version? At 20ft off the ground an 80m version will be mostly omni directional on 80m then four lobes on 40, eight lobes on 20, etc. A 40m version will be mostly omni on 40, four lobes on 20, 8 lobes on 10, etc.
 

K6GBW

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At 20 feet you signal on the lower bands is basically going to be a blob, so it will be good for NVIS out to about 300 miles. To get any distance you'll have to stick to the higher bands. What kind of operating are you trying for?
 

kk9h

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I have a Myantennas 40-10 meter multiband end fed antenna that I use for Field Day, portable and on vacation. The pattern it will have will depend entirely on how high it is and what band it is being used on. If it is only 20 ft. high, on 40 it will behave exactly as K6GBW described, a high take-off angle signal (approaching straight up) without much directionality, great for close by contacts, but not so much for DX. As you go higher in frequency (assuming it’s still at 20 ft.) with 20, 15 and then 10, it will begin to develop some directionality and the signal take-off angle will start to go lower toward the horizon. When I use this antenna on vacation I am able to get it up about 45 ft. using the nearby trees and have had great success working DX with it, even on 40 meters. I hope this helps answer your question.
 

merlin

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One 40 meter end fed I set up was feed at 45 foot from the tower. A slopper configuration, about 30 °
The low end away from the shack. It was more omni directional on 40 and lobes increasing all the way to 6 meters.
I never tried 2 meter so ??
I later changed that to T2FD with noticeable improvement in gain.
Cheers.
 

KA4DPO

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The antenna you described sonds like a monopole antenna. I have built a lot of single band monopoles over the years and have learned to avoid a half wavelength. The RF voltage at the end of a half wave antenna is extremely high, as is the impedance. Better to use something a bit longer or shorter to avoid RF all over everything. I also stay away from the torroidal Un-Un's that introduce too much loss, and they can arc under some conditions.

For 40 meters, an antenna that is just 15 percent longer or shorter than a half wave can be end fed with a simple L network that will have an SWR bandwidth of less than 2:1 acroos the entire 40 meter band. Regardless, you still need a very low impedance return path (radial system) to maximize antenna currrent. Best of luck with the monopole.
 

prcguy

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The antennas described here are exactly a half wavelength on their lowest band and exact multiple half wavelengths on all harmonic bands using a broad band 64:1 or 49:1 RF transformer. They do have very high voltage on both ends on the lowest design band but its not a problem. I run full legal limit on mine and there are 10s of thousands in use right now and they work great with virtually no loss and they do not place any RF on the coax when used within their resonant bands. Its always best to use a good choke balun, but if you don't you should not have any RF on the coax problems.

The antenna you described sonds like a monopole antenna. I have built a lot of single band monopoles over the years and have learned to avoid a half wavelength. The RF voltage at the end of a half wave antenna is extremely high, as is the impedance. Better to use something a bit longer or shorter to avoid RF all over everything. I also stay away from the torroidal Un-Un's that introduce too much loss, and they can arc under some conditions.

For 40 meters, an antenna that is just 15 percent longer or shorter than a half wave can be end fed with a simple L network that will have an SWR bandwidth of less than 2:1 acroos the entire 40 meter band. Regardless, you still need a very low impedance return path (radial system) to maximize antenna currrent. Best of luck with the monopole.
 

KA4DPO

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I tried that design many years ago using a 49:1 Un-Un transformer, and a ferrite choke to keep RF out of the shack. Except in the cases where the antenna is almost exactly 1/2 wavelength, RF current will appear on the coax shield, hence the choke. My experience has been that the 49:1 and 64:1 transformers only provide a 1.5 to one or less match in a very narrow range of frequencies, this became more pronounced as I moved to higher multiples ( I was using an 80 meter half wave at 3.6 MHZ). I tested it using a network analyzer and sure enough, the transformer loaded the heck out of it.

So don't take my word for it, run 500 watts on CW or SSB for about a minute, then go out and touch the transformer (Un-Un). It will be hotter than hocky sticks because that is where most of the RF power is being dissapated. The antenna will radiate the rest minus the additional losses in the coax and earth losses. Sorry I can't be more help to you.
 

KA4DPO

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A lot of these questions are the stuff that noobs ask about store bought antennas. I notice very few use their call sign.
 

prcguy

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The problem is most people making their own version are using the wrong ferrite mix and that can heat the core up more and also provide too much inductance on the higher bands. Most designs I've seen call for a #43 mix and a single 2.4" core of 43 might only be good on 160 through 40m. If you stack cores it compounds the problem and you have to choose a still lower permeability ferrite.

Companies like MyAntennas know the best formula and their standard models that have what I believe is two cores handle 1kW SSB and 250W continuous. Their 3 core versions handle 2kW SSB and about 350W continuous. If you make one with different ferrite material you may not get the same power or frequency ratings.

I mentioned before there is no appreciable RF on the coax within their resonant bands and if you light one of these up too far out of band they will put a lot of RF on the coax. I've made a lot of these antennas, probably two dozen or more in sizes ranging from about 100W SSB to 2kW, so I have many years of experience and its all been very good. For my permanent full legal limit installs I'll use a commercially made MyAntennas but for lower power my home made versions are very popular with the local hams and they constantly praise them for their ease of deployment and also the performance.

I had a few chats with Danny that owns MyAntennas and he commented about some online posts where people who have never even used a EFHW are giving all the reasons why it can't work. He just laughs all the way to the bank with probably 10s of thousands of these sold so far with no problems to speak of. I know you have made at least one and you might consider any problems you may have might be from the ferrite mix or the way its wound. Early on I opened up a MyAntennas transformer and saw the way they treat the turns and spacing and copied that. Its a little different that what you might find online and little things like this can skew VSWR and performance.

Edit:
I'll add just a little more to this post and say I have tested a 40m EFHW against a resonant center fed dipole in the exact same location and height and there was no perceivable difference in signal level to anyone. For an 80m version there is very little difference in performance or radiation pattern compared to the same 133ft of wire fed in the center with ladder line to a balanced tuner. Sure there might be a fraction of a dB loss in the transformer or maybe up to 1dB overall loss on some higher band, otherwise exciting 133ft of wire in the center or the end gives you the same basic results and you would have a slight amount of loss in a center fed setup in the tuner.

I tried that design many years ago using a 49:1 Un-Un transformer, and a ferrite choke to keep RF out of the shack. Except in the cases where the antenna is almost exactly 1/2 wavelength, RF current will appear on the coax shield, hence the choke. My experience has been that the 49:1 and 64:1 transformers only provide a 1.5 to one or less match in a very narrow range of frequencies, this became more pronounced as I moved to higher multiples ( I was using an 80 meter half wave at 3.6 MHZ). I tested it using a network analyzer and sure enough, the transformer loaded the heck out of it.

So don't take my word for it, run 500 watts on CW or SSB for about a minute, then go out and touch the transformer (Un-Un). It will be hotter than hocky sticks because that is where most of the RF power is being dissapated. The antenna will radiate the rest minus the additional losses in the coax and earth losses. Sorry I can't be more help to you.
 
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