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Anyone amateur radio ops here have experience with end fed HF antennas?

  1. Feb 20, 2015 #1

    Averagesupernova

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    Having not been set up with a station for quite a few years I am thinking of setting up an end fed antenna for HF. It seems the only way I will enjoy a little 'hamming' again is to start out simple and quick. Trying to avoid clutter in the middle of the yard. I have enough tower sections get a little ways up in the air using a house bracket. Thinking about end feeding a wire using the tower as a counterpoise. Antenna books mention schemes like this but was wondering if anyone here has experience with it. I have enough real estate at this particular location to get about 70 feet of wire off of the tower. This would be a little over 1/4 wave for 80 meters. My concern is excessive RF voltage when the wire would be a 1/2 wave on 40 meters. Most of my experience with antennas involves center feed. Has anyone had experience matching antennas like this with a toroidal balun versus an actual balanced matcher? Contemplating scrounging around for an EF Johnson Matchbox or maybe something new. I understand there are some new products out there that are actual balanced matching networks instead of the simple T-network.
     
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  3. Feb 20, 2015 #2

    nsaspook

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  4. Feb 20, 2015 #3

    Averagesupernova

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    Probably won't be using coax since the high feedpoint impedance on some bands. Most likely homemade ladder line or something similar. This is the reason I am considering a balanced matching network. Nothing is cast in stone here yet. Still going over it in my mind. Thanks for the reply nsaspook.
     
  5. Feb 20, 2015 #4

    nsaspook

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    We used T type matching networks and combiners to feed several transmitters on different bands into one antenna (usually a long-wire or a trussed whip) by using rather large HELIAX interconnect cables to handle the high-voltage requirements. A homemade line would be a lot cheaper at $50 a foot for HELIAX. Have fun.
    http://www.commscope.com/catalog/andrew/product_details.aspx?id=1464
     
    Last edited: Feb 20, 2015
  6. Feb 20, 2015 #5

    Baluncore

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    The problem with an end-fed sloping wire is that it has directionally variable polarisation. As described, your antenna will radiate horizontal to the sides of the wire and vertical in the line of the wire. Because it is close to the ground in wavelengths, horizontal polarisation will cancel with the reversed induced ground currents.

    Maybe you should be using vertical polarisation which will image as twice the height in a ground plane mirror. You might be better insulating both ends of your high wire and feeding it as a capacity hat from near the centre. You could then run a wire on the ground surface below the high wire as the counterpoise / ground. Keep the high wire well clear of the ground at the low end. Use ladder line to drive the mid-point of a vertical wire that connects the mid-points of the high and low wires. That will keep impedances high with reduced losses in the feed-line, so one tuner only will be needed at the transmitter.
     
  7. Feb 22, 2015 #6
    I've had some experience with end fed antennas. Enough to know that I don't like them. My motivation for experimenting with them was the same as yours. I just wanted to get on the air quick and simple. It may be ok for qrp but if you want to run any kind of power you really need to get the rf out of the shack. And the best way to do that is to have good matching. I was never able to get good matching with an end feed. There may be ways to do it but the best I can remember they were all not quick and simple.
     
  8. Feb 22, 2015 #7

    davenn

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    yeah great for hilltopping, throw a long wire up into the trees and go for it! :wink:

    The majority of decent ATU's will have an output for an endfed antenna
     
  9. Feb 22, 2015 #8

    Averagesupernova

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    Got my hands on an old EF Johnson matchbox balanced tuner. Will try to fit my old 80 meter half wave center fed with ladder line as a multiband antenna onto the property. I am not afraid of end feds that are fed CORRECTLY. A j-pole is in fact an end fed halfwave with a 1/4 wave stub on the bottom to transform to a low impedance. Had a homemade one years ago with another half wave stacked on top phased with a 1/4 stub. Worked great. The problem with my current situation is that I want to run multi bands and while it works ok to end feed a half wave with only one side of a balanced transmission line that is 1/4 wave long, that scenario won't work on all bands. Back to the tried and true.
     
  10. Feb 23, 2015 #9
    This web page pretty much reflects my experience with end feeds. Let us know what you end up doing and how it works out for you.
     
  11. Feb 23, 2015 #10

    Baluncore

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    All is not lost. There are a number of end fed systems that do work.
    For example, travelling wave wires terminated with a resistor, such as the beverage or rhombic antenna.

    If you have a single tower you can stretch two wires from the top of the tower to two points on your boundary. Those two wire lines can be driven differentially through a balun as a “V” antenna. If the two wires travel in opposite directions from the tower, it becomes a centre fed inverted “V” antenna.
     
  12. Feb 23, 2015 #11

    Averagesupernova

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    The only times I have used balanced feeders on the center fed is at various field days and I liked it pretty well. I used a t-match antenna tuner and had no problem with the toroidal balun transformer between the t-match and the balanced feedline. However, I don't believe I was on all bands and I used a random length of transmission line. The tent with the radio was put down where the transmission line ended so there was no extra feed line to deal with. Even though I had no trouble with the balun (4:1 voltage balun) I want to avoid this scenario since it is possible that some bands will create quite a high impedance at the station end of the balanced feedline and this can cause balun troubles. Hence the Johnson matchbox. The one thing I am concerned with is running ladder line in my house. Ideally I would like to have the ham gear up on the second story where the ladder line can just be run through a converted window but that scenario is not likely to turn into reality so I am afraid it will have to run through the wall into the basement and along a ceiling joist or two. There is some copper plumbing and furnace ducts in the vicinity and I am a bit concerned with that. I have read of some hams claim to run two pieces of RG-8 side by side taped together as if they were balanced line. Ground the shields together at the transmatch and treat the center conductors as a pair of balanced lines. Once outside the house switch to the ladder line. While this sounds tempting I don't think I will try it. Antennas and antenna systems are very interesting critters to say the least. The link provided by TurtleMeister has a lot of info in it and will take me a while to go over. At first glance it seems there are some things there that contradict what I have read out of the ARRL antenna handbook. We'll see.
     
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