Resonant multiband vertical antenna vs non-resonant vertical with autocoupler at base

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by M0AGP, Jul 11, 2020.

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  1. M0AGP

    M0AGP Ham Member QRZ Page

    Naively, it seems like using an autocoupler at the base of a reasonably long vertical radiator (call it 43 feet - roughly 5/8 wave on 20m) should work OK for frequencies below the point where numerous lobes start appearing and much more of the radiation goes upwards. It seems like a 43 foot vertical might be ok up to around 18 MHz by that logic, but maybe not so good for 15 or 10m (?).

    Comparing such an antenna with a fan-vertical type, like the DX commander, where I think the resonant wires are all quarter wave for 40m - 10m (apart from the 15m band which uses the 40m element as a 3/4 wave), assuming the ground radial systems are the same for both, would one expect about the same performance?

    I guess the 5/8 wave on 20m would outperform the quarter wave case... how about 30m and 40m?

    Seems like the fan vertical could take the full legal limit, but maybe a high power autocoupler could be pricey.

    The question pertains to 18MHz on down as a fair comparison.

    People can fool themselves into thinking all is well when the tuner in the shack shows a 1:1 SWR, as we know (little power might be getting to the antenna), but can we also fool ourselves with autocouplers at the antenna end of the transmission line?

    In other words is a non-resonant vertical with an auto-coupler at the base "just as good" as a resonant vertical?
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

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  3. M0AGP

    M0AGP Ham Member QRZ Page

  4. K8JD

    K8JD Ham Member QRZ Page

    Antenna Experiences.
    Yes there is actually gain in a 5/8 Wave 20 M ant (43 ft) over the common trap (QW) vertical.
    I Agree the 43 Ft length is pretty good from 5 to 18 MHz but 17 M and above has some loss of DX gain due to high angle lobes strengthening as the freq goes up/ I think you can't loose when you use a remoted controlled tuner right at the base of this vertical.
    I made a 20 M EDZ antenna that has two 43 ft segments of wire fed in the center. Using 450 Ohm balanced line to a MFJ balanced line tuner in the shack. Great antenna from 5 to 18 MHz.
    Actually notice the gain on 20 M , broadside to the wire, increased signals over a GP vertical !
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  5. HB9PJT

    HB9PJT Ham Member QRZ Page

    The antenna with the tuner can be better. Because the resonant antenna is only lambda/4, but the antenna with the tuner can be lambda 5/8 and therefore has more gain.

    73, Peter - HB9PJT
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  6. PA5COR

    PA5COR Ham Member QRZ Page

    My 77 feet long vertical has the MFJ 998 legal limit auto tuner at the bottom feeding it, using that on 160 - 20, though on 20 it is a throw up if it is betteras the FD-4 OCF.
    for 18to 10 I'm using the Imax 2000, does fine there.
    From 160 to 10 i can chose horizontal/vertical on all bands.
    The FD-4 OCF even works fine on 6 meters, SWR 1.3 there.
    The FD-4 has a coil and 30 feet of wire making it resonant on 160 as shortened antenna
    Mostly used there as receiving antenna though..
  7. M0AGP

    M0AGP Ham Member QRZ Page

    Wow - looking at your nice high antennas on your QRZ page I can see that the Netherlands must have less restrictive planning restrictions than the UK (here an antenna is considered a "building" and so planning permission is required - similar to US HOA restrictions, but country-wide). Whilst it is not the topic of this thread, I expect you have a lot of data on which antennas are better for DX...
  8. PA5COR

    PA5COR Ham Member QRZ Page

    I had my run in with local planners and housing estate owners, resulting in my action against the city and then owners of our rented home costing them 7 million guilders ( 3 million euro's) to do them up.
    As ex policeman kid and ex customs officer i know the law just quite well, never had a problem putting up antenna's after our "little costly" interference.
    Even wrote them to say i had them up and if they had objections, never heard back from them, that was 15 years back, according our law they are now legal.
    Added 3000 feet of copper wire in/on the ground for radials for the vertical for 160 - 20.

    Normally everything up to 5 meters above the roof is free, no permission needed, only if you live in a protected valuable area with architectural beauty or inner city, though the law is quite strict to allow hams to have antenna's.

    I'm no antenna guru, we have better members here, but for my one of a row housing with the 100 x 25 feet plot i made all the use of the ground and roof I have, neighbours don't mind, I'm helping them out where I can, so they don't mind my escapades on the roof ;)
    Last edited: Jul 12, 2020
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  9. M0AGP

    M0AGP Ham Member QRZ Page

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  10. M0AGP

    M0AGP Ham Member QRZ Page

    Here’s a follow-on idea from the 43 foot vertical with the auto-coupler at the base: as this 43 foot tube/wire takes care of 40, 30, 20 and 17m, what about adding a additional “fan” elements that are resonant on higher bands?

    I wonder if the auto-coupler would effectively end up feeding the resonant elements by preference, or path of least resistance, in some sense. Say for example you wanted to add 6 meters for some sporadic E fun. I wonder if the autocoupler would effectively ignore the 43 foot vertical (like a high resistance) and feed the 6 meter one? Or maybe it would just shoot all the 6m energy straight up...

    I guess a relay could switch between the vertical wires given there is already a power feed going out there.

    Of course the 43 foot vertical and the alternative fan vertical elements form a coupled system so behaviour might be a big mess with lobes all over the place on higher frequencies even if a relay was used to switch between vertical wires...

    Might be interesting to try and model this! (Expecting it has been tried in the 1930s...)

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