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Can’t get SWR below 1.5 in HF. Can trees matter?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K1THE, Sep 20, 2021.

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  1. K1THE

    K1THE Premium Subscriber QRZ Page

    I have been using a Par EndFedz Mk2 Trail Friendly 40/20/10 though using the matchbox from an EndFedz EF-QUAD (with Vibroplex’s blessing) so I could transmit at more than 25W. On all three bands I have very nice SWR - for 20m and 10m around 1.1. For 40m 1.1-1.5.

    Today I switched over to using the radiator that actually came with the EF-QUAD matchbox - heavier gauge wire and full-size at 40m rather than being electrically-lengthened like the Mk2. And I seem to be getting better receive performance with it.

    However, I can’t get SWR much below 1.5 on any of the bands, despite the charts that come with the antenna saying it should bottom out at 1.1. By trimming (well for now, folding back on itself) I can move the minimum SWR frequency but I have not been able to make SWR go lower.

    Everything in the shack is the same. And the house end of the antenna is in the same place. The antenna is at the same angle (perpendicular) to the house. Now, since this antenna is 25’ longer than the other one the far end is in a different place, making this antenna actually further off the ground than the other one. However it also goes closer to trees. It is not touching any branches or limbs but does come within a couple of inches of some decent-sized limbs in a few places. Could that be messing with my SWR?
     
  2. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    What is wrong with 1.5 when using an EndFedz ?


    73
    K0UO Rhombic Antenna Farm is located at the Kansas QTH with over Two miles of Wire in the Air & On the Air, “The RF Gotta-Go-Somewhere"!
     
    AA5BK, WB5YUZ, KU3X and 1 other person like this.
  3. K1THE

    K1THE Premium Subscriber QRZ Page

    Fair question!

    Not saying it’s wrong, just wondering if I’m doing something wrong somehow since the other EndFedz had better SWR (according to my analyzer) and this one should be (according to manufacturer’s claims) be better than than what I’m getting.
     
  4. AK5B

    AK5B Ham Member QRZ Page

    Maybe it has less loss than the others; A low VSWR can be indicative of loss in the system. Try measuring a ground-mounted monopole with only a ground rod and no radials. Add 32 ground radials and re-measure---the SWR will be higher (betting dollars to donuts in all cases).
     
    UT7UX, K1THE and WB5YUZ like this.
  5. K1THE

    K1THE Premium Subscriber QRZ Page

    Let me describe the setup a bit more first. I also have an additional datapoint.

    Because of my living situation I'm pretty constrained as to where I can have the feedpoint of the antenna -- I was allowed to screw a hook into the exterior windowframe. The matchbox is is attached (with a short bit of rope) to that hook. A 1-foot length of coax connects to the matchbox and to a common-mode choke just inside the window. Then a 12-foot length of coax goes from the CMC to the radio. This is all the same with both radiators. There is no ground or counterpoise because I'm not allowed to run a wire down from the window. And with both radiators I measured the SWR with an antenna analyzer by connecting it to the cable that connects to the radio -- because I wanted to measure the SWR the radio sees.

    The additional datapoint:
    I decided to measure the SWR before the CMC. When I did that, the minimum SWR dropped to 1.1-1.2 on most bands, and dropped noticeably on all four bands. With the previous radiator I had measured SWR both at the radio and before the CMC and with that radiator they were virtually the same. So I assumed (danger will robinson) that would be true with this radiator. Obviously, apparently not.
     
    Last edited: Sep 20, 2021
  6. WE4E

    WE4E Premium Subscriber QRZ Page

    This might be the issue right here. Far and away, the majority of "end fed" antennas rely, on some degree, to the shield of the coax to balance the antenna. The design of the matching transformer will dictate to what degree that's so. You should, at a dead minimum, move the CMC closer to the radio and use the 12' section of coax between that and the transformer. You might also consider a counterpoise wire, even if it's temporarily strewn across the floor. I have a friend here using a 24' Ultimax on the ground floor of a 3 story apartment building, and he has a 33' wire attached to the ground lug on the radio. He's not pegging any S meters, but he gets heard. Not ideal, and violates a lot of conventional wisdom, but you get my point. The RF needs a return path. You can give it one or it can find its own - your call.
     
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  7. K1THE

    K1THE Premium Subscriber QRZ Page

    Here are some additional measurements I've made to try to figure out what's going on:
    1. Remove the antenna from the choke, attach a dummy load to the choke, connect the antenna analyzer at the radio end of the cable between choke and radio: dead flat at 1.0 on all bands.
    2. Attach the antenna analyzer at choke end of the cable that goes from antenna to choke (i.e. measuring close to feedpoint with no choke): SWR bottoms out at 1.2 in 40m band, is under 1.5 for the entire 40m band.
    3. Connect the antenna/choke cable directly to the choke/radio cable (i.e. no choke) and attach analyzer at radio end of choke/radio cable: SWR still bottoms out at 1.2 and is still under 1.5 in the 40m band, but the frequency of minimum SWR drops a little.
    4. Connect the antenna/choke and choke/radio cables to the choke, attach analyzer at radio end of choke/radio cable: SWR now bottoms out at 1.6 and gets over 2.0 at the ends of the 40m band. Minimum SWR occurs at the same place as in (3).
    So the cable from radio to the choke doesn't affect minimum SWR on its own (though it does change the frequency where the minimum SWR happens). And the choke doesn't affect minimum SWR on its own, but choke AND cable affect minimum SWR. But they didn't affect it for the other radiator.

    So even if it isn't that big a deal to operate with the higher SWR I'm curious as to why this is all happening.
     
  8. WE4E

    WE4E Premium Subscriber QRZ Page

    Because every time you change the coax/choke arrangement, you're changing the antenna system. The antenna doesn't stop at the SO239 on the transformer.

    Resonance and match are two completely different things. As you've measured, the match on your dummy load is pretty good. I don't expect that it will radiate much of a signal however. Can you measure R and X separately?

    What does the radio think when you hook it up?
     
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  9. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    You have read the manual, right, and not just looked at the charts? You're supposed to adjust the antenna to by cutting the strategically placed stubs, not by folding the wire back on itself. If you didn't follow this procedure, put the wire back at it's original factory-provided length, read the manual, and then adjust the antenna.

    In any event, I think you are putting too much emphasis on SWR as an indicator of antenna performance. The fact that you are being heard better with the wire that was original equipment is really all you need to know.

    Good luck!
     
    K1THE, AK5B, WN1MB and 1 other person like this.
  10. KI4ZUQ

    KI4ZUQ Ham Member QRZ Page

    What does your analyzer say about the R and +/-jX values at minimum swr? Could be your antenna tuner has run short of C or L ....
     
    WN1MB likes this.

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