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Multi-Band Wire Antenna Question

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N4LCV, Feb 22, 2013.

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  1. N4LCV

    N4LCV Ham Member

    I have put up a "Wireman Flattop" antenna. It's 135 feet long, & is fed with ladder line. There is a 4:1 balun where the ladder line transitions into a short piece of RG-8X to connect to an MFJ 929 Auto-tuner. It's suspended between two large trees and is up about 35 feet. When I connect my MFJ 259B Antenna Analyzer up to it, what I find is a very high SWR on 80, 40, 15 & 10. These are basically the bands I work. The only band where it's even fairly close is on 20 meters. There are some dips, but none of them, except on 20 is anywhere even close to one of the bands we can operate on. Is this typical of a Multi-Band wire antenna? If someone else out there has a "Wireman Flattop" I'd like to hear what the SWR in your shack is like. I can tune it with a tuner, but it takes a LOT of tuning on all of these bands to get a reasonable SWR. Another Ham told me recently about a friend who has an 80/40 dipole up and with a tuner, he supposedly is able to work all the other bands easily without a lot of tuning and no tuning at all on 80 and 40. When my antenna is tuned properly, it gets out pretty well, but I'm wondering if an auto-tuner is the best way to go considering the very high SWR that has to be tuned. I have an MFJ 941E Versa-Tuner II that I could use instead. What is the collective wisdom of the group about that?

    Thanks & 73

  2. WB2WIK

    WB2WIK Premium Subscriber

    The 4:1 balun may be the wrong choice, depending on the length of the ladder line.

    The antenna system you describe is complex and how it "matches" at the bottom end of the RG8X will depend entirely on the length of the ladder line and the balun. It's not an easy task to make a fixed-length dipole match well on even harmonic frequencies; a "trick" commonly used is to change the ladder line length for each band, and use the ladder line as a matching transformer. There are some fairly easy ways to do that, using a "patch panel" with ladder line sections installed between pairs of banana jacks (or similar), so just moving some jumpers around changes the line length.
  3. N4LCV

    N4LCV Ham Member

    Thanks. This whole system came as a kit, including the ladder line cut to length and the balun. It's all put together as the Wireman's instructions specified.
  4. WB3BEL

    WB3BEL Ham Member

    Maybe you could quantify what you mean by "Very high VSWR" by band.
  5. W5DXP

    W5DXP Ham Member

    Here's some info on just such an antenna:

    Interfaced to a 1:1 current balun, here are the optimum feedlengths per band for avoiding a tuner.

    The yellow region shows the lengths that I use. A fixed length of 100 ft. of ladder-line is a good compromise.
  6. WB2WIK

    WB2WIK Premium Subscriber

    I couldn't find an antenna that fit your description on The Wireman's website. He does list a "Flat Top Antenna Kit," but that says it comes with 75' of ladderline and doesn't mention anything about a balun. He also does state it requires an antenna tuner.
  7. K8JD

    K8JD Ham Member

    My 250 ft "flat top " is center fed thru a 1:1 balun, 250 ft RG8x coax and has a 1.2:1 SWR at the bottom end of the 160M band, where I operate. NO TUNER.
    My 130 ft "flat top" is centerfed with a 1:1 balun, two hundred ft of RG8x coax and has 1.2:1 in the CW band on 80M where I use it. NO TUNER.!
    M y 90 ft (flat top) dipole antenna is center fed with 450 ohm twinlead right to my balanced input tuner with NO internal balun. It works from 60 to 20M with the tuner adjusted for less than 1.5:1 SWR on each band.

    Sticking a 4:1 Xfmr on the end of a random length of balanced line is guesswork as to the final Z at the radio.

    Measuring the SWR etc, with an analyzer, at the end of the short coax pigtail is futile since this kind of antenna is always used with some kind of tuner, it is NOT designed to be 50 ohms !!!!!.

    Get rid of the 4:1 and use a true balanced input tuner (the kind with NO INTERNAL 4:1 balun) at the end of the ladder line.
    Last edited: Feb 22, 2013
  8. KM3F

    KM3F Ham Member

    You got an assembly that is over complex in my opinion.
    I run 126 foot dipole with a 40m addon element otherwise known as a fan arrangement.
    Fed with 50 ohm coax and worked with an old Heathkit 2060 tuner.
    The feedline has a coil of feedline out at the remote switch to help limit any common mode.
    I can tune any band with this setup and have no feedback issues.
    May not be as efficient on every band but I do use it above 40m, having beams to switch to.
    Good luck.
  9. W1FBV

    W1FBV Ham Member

    Use your antenna tuner.

    73, Jim W1FBV
  10. K9ZMD

    K9ZMD Subscriber

    Bingo. Whenever I've used a doublet antenna with an auto-tuner (either an RT-11 or SG-239) I've always found a couple bands that could not be matched with a single length of balanced line. Changing the balanced line length moved the problem to different bands. However, when I used my Heathkit SA-2040 instead of an auto-tuner, there was no problem finding a match on any band.
  11. N4LCV

    N4LCV Ham Member

    The internal tuner on my Yaesu 767 says that the SWR on all bands is at least 17:1 and higher. The antenna is the Flat-top kit on the Wireman's site. I talked to the Wireman, himself, "Press" (I guess it's short for "Preston") and told him that I wanted to use the MFJ antenna tuner. So he sold me, at the same time, the balun, which is a short length of a small coax and a whole lot of small toroids that are just big enough to slide over the small diameter coax. There must have been 30 or 40 of the toroids. He said it was what I needed to go from the ladder line to the short run of coax. The antenna tuner can only be fed with a PL-259.
  12. W5DXP

    W5DXP Ham Member

    The 30-40 toroids slipped over coax is a 1:1 choke. Do you have a high SWR with that choke installed? Are you using the coax output on your tuner with nothing connected to the balanced wire banana plug sockets? Do you disable the internal tuner when the MFJ is in use? How long is your ladder-line?
  13. N4LCV

    N4LCV Ham Member

    The ladder line is 75 feet long. The internal antenna tuner is turned off when the MFJ is in use. OK, my bad on what I was calling a balun. I believe you are right that it is a 1:1 choke. Yes, I have a high SWR with the choke installed. The MFJ does not have balanced wire banana plug sockets. As I said, the only way you can connect an antenna to the MFJ is with coax and a PL-259. There are 3 and only 3 connections on the back of the tuner. One is marked "Transmitter" and the other two are marked "Coax 1" and "Coax 2." There is one binding post for a wire antenna and a ground. The 75 feet of ladder line isn't long enough to reach the rig. "Press" said that this is the way I should connect the antenna to the rig.
  14. W5DXP

    W5DXP Ham Member

    EZNEC says that 75' of ladder-line used on a 135' dipole will result in an SWR of 34:1 on 3.75 MHz and 60:1 on 7.15 MHz. Why would anyone be satisfied with those terrible SWRs? Please change the ladder-line length to 96 feet. EZNEC says that will give you an SWR of 6.5:1 on both 3.75 MHz and 7.15 MHz, an easy match for an external tuner. That length should also work fairly well for 30m, 17m, and 15m.
  15. N4LCV

    N4LCV Ham Member

    Thanks, Cecil, for the info. What would the SWR be in the phone portion of 20 and 10? Also, if I were to build an 80/40 Fan Dipole, cut for the center of the phone portion of each band and fed it with RG-8X, what would the SWR be in the phone portion of 20, 17, 15, 12 & 10?


  16. KO6WB

    KO6WB Premium Subscriber

    Nowhere does it state that an antenna has to be resonant to work. Any length of wire can be and is an antenna. All you have to do is to properly transfer the power to it and it'll radiate. Maybe not very well but it'll still do something. A high SWR does not stop RF from radiating from an antenna. So quit worrying about the SWR of the antenna. You do have to worry about the SWR to the rig though. Manual tuners usually work a wider range then auto tuners and they both are making it possible to transfer power to the load (antenna in this case). If you could put the tuner at the antenna with the coax from the tuner going in to the shack, then things will work just a bit better. However, nowhere does it say you can't have resonant antennas for all the bands you wish to work. These usually match without a tuner but remember it's the transfer of power to the load that does the work.
    Antennas are constructed from simple materials using well known physics. There are no magic antennas nor any that are truly mysteries. They all have certain properties that make them work better in some ways and worse in others. No single antenna does it all, all of the time.
    The matching method Cecil has in his website is a sort of simple tuner in a way. You vary the feedline length to vary the impedance seen at the end. It makes it possible to transfer the power to the load more efficiently. If you have coax feeding into an antenna that has the same impedance as the coax then no matter what length of coax you used the impedance will always be the impedance of the coax and the SWR will never change.
    To show how simple antennas are to make with just wire, here is a presentation that shows a number of ideas for your consideration; Antenna Basics_ARRL_Ohio_8-11-12.pdf.
    These are antennas known to work and work very well.
    Hope this helps
  17. W5DXP

    W5DXP Ham Member

    Unfortunately, the SWR on 14.2 MHz would be 80:1 and on 28.4, it would be 47:1 according to EZNEC. That's why it is better to vary the length of the ladder-line. I don't have a fan dipole model but we know the SWR for that RG-8x fed fan dipole would be too high on 20, 17, 12, and 10. It would probably be acceptable on 15m because 7 MHz times 3 = 21 MHz.

    True, but we should be aware that a high SWR can prevent RF from ever reaching the antenna. For instance, with 75' of RG-8x and an SWR of 50:1 at the antenna, only ~18% of the transmitter power makes it to the antenna. That fact is somewhat masked by the SWR = ~10:1 measured at the shack. As a rough rule of thumb, I like to keep the SWR on my coax to less than 10:1 all along the coax feedline.
    Last edited: Feb 24, 2013
  18. W9JEF

    W9JEF Ham Member

    I agree with KO6WB. Your SWR meter is merely showing the match between your rig and tuner. It says NOTHING about SWR on the antenna feedline. All antenna wires thermselves (except beverage and other wave antennas) will have large values of SWR. It's the feedline where the losses occur. Any coax on the output side of your tuner will soak up power, (unless SWR is low). You need a link-coupled, or other true-balanced tuner to feed an 80 meter doublet on all bands. I've found the lowest loss, lightest-weight, and and least expensive transmission line for HF to be #14 or #12 insulated house wire with donut-shaped spacers cut from the bottoms of plastic juice bottles.
  19. N4LCV

    N4LCV Ham Member

    The real reason that I am concerned about the SWR doesn't have to do with whether or not my signal is getting out. Reports that I've gotten on the antenna is that it radiates very well. The problem is that last Friday when I had a chance to get into a real QSO with a friend, the rig kept cutting out. It would just stop transmitting, and the only way to get it back online again was to go back to the MFJ auto tuner and retune. It would make it's usual grinding, snapping sound and the radio would begin transmitting again, most of the time. I had one time when nothing I did would get it back online for 2 or 3 minutes, then all of a sudden, it worked and I was able to transmit again. I've had the radio checked by a good repair guy and he can't find anything wrong. So we are thinking that there must have been some problem with the auto tuner tuning that high an SWR. There has never been a problem with the tuner before. So, now, I've taken the auto tuner out and replaced it with a MFJ 941E Versa Tuner. I hope to work my buddy again in the next day or two and we will see if the manual tuner makes a difference. When I bought the Flattop, I thought I was getting an antenna that I could work on all bands, with a tuner, that would get out better than a G5RV. The local nets are on 80, I work my buddy on 40, but I would also like to work on the higher bands, 20 & 15 especially. If anyone can suggest a better antenna system for my needs, I will be glad to consider all possibilities. I have tried a Carolina Windom, but couldn't tell much difference between it an a G5RV. For a number of reasons, I'm pretty well stuck with a wire antenna suspended between two trees. A center support is pretty much out of the question.
  20. KO6WB

    KO6WB Premium Subscriber

    Can you make a horizontal delta loop? An example of this is in the download you can get here; Antenna Basics_ARRL_Ohio_8-11-12.pdf. If you can make one for 80 meters it'll work all harmonics, even or odd. So, a 3.5MHz loop will tune 7, 10.5, 14, 17.5, 21, 24.5, 28MHz without the need for a tuner. If you can't put up a full wave loop for 3.5MHz and want to make it as large as possible, just too big to match 40 meters. Then you'll still need a tuner. Look into this approach and others that are shown in the link.
    I think you'll be happy with what you can do.
    Have fun
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