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Inexpensive way to check radial effectiveness?

Discussion in 'General Technical Questions and Answers' started by KI1SPK, Oct 13, 2018.

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  1. KI1SPK

    KI1SPK Ham Member QRZ Page

    Hi everyone,

    I appreciate all the help in getting my first station set up for a complete newcomer. I have an Icom 7300, homebrew 33' vertical elevated 12 ft with about 15 radials, and a LDG RT-100 remote tuner.

    I've been reading a lot on the forums of # of radials, elevated vs. on the ground, tuned vs. non-tuned, etc.

    Without purchasing additional equipment, is there a way I can get an idea of how well the radials are doing reducing ground losses? Using the Icom SWR graph on 40m and no tuner, the SWR is about 2.0 across, but I'm not sure how much that tells me about ground losses.

    Thanks!
     
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I think it doesn't.

    A 33' vertical with even 4-6 ~33' long radials should work well on 40 meters, but even with a remote tuner is still compromised on other bands, especially 20m and 10m where its feedpoint impedance should be thousands of Ohms and the tuner runs the risk of damage.

    Did you intend this for 40m work only?
     
    NH7RO likes this.
  3. N4MTB

    N4MTB Premium Subscriber QRZ Page

    Add a 20 meter stub, about 16.5 to 16.75 feet
     
    NH7RO likes this.
  4. KI1SPK

    KI1SPK Ham Member QRZ Page

    Thanks for the replies

    I made for use on 40m but then thought about multiband use. I made a 20m vertical but get tired of switching them over.

    I may try a nonresonant length for fun, maybe 43’

    I’m not familiar with stubs. I can give it a try. It looks like a shorted or open piece of coax connected with a T to pass the 20m signal through and filter others?

    Thanks.
     
    VK6ZGO likes this.
  5. NH7RO

    NH7RO Ham Member QRZ Page

    Actually it should be very easy for you to have multiband operation by merely adding parallel radiators of the appropriate lengths for the other bands so it becomes a "fan groundplane."
    One coax feedline and no bandswitching required---once the elements are tuned you're good for instant band changes without ever having to retune.

    If you search the antenna forum for "fan vertical guidance" you will see my old thread about this type of no-tune multiband vertical. I am still using mine and while it was origianlly only for 20-17-15m I later added 10m. I only have around a dozen radials that run close to .25 wave length on the various bands (2-4 per band) and it is elevated 8 feet above ground here---I've been very pleased with this inexpensive homebrewed job that only required a couple of fiberglass poles stuck together atop a 2X4 and some copper rings for element and radial attachments.

    For a commercial version that's really slick (albeit a ground-mounted version) search for "DX Commander" and Collin's creation will come up complete with a few great YouTube videos.

    73,

    Jeff
     
    Last edited: Oct 13, 2018
  6. NH7RO

    NH7RO Ham Member QRZ Page

    PS: FWIW, Rudy Severns, N6LF found that a ground plane mounted 4 feet above average ground with 4 radials between 0.15 to 0.40 wavelength on average performed as well as a ground-mounted one with 120 radials---really kind of indicative of reduced ground loss, I'd say. As for how much I don't know; but at this fair increase in performance I wouldn't worry about it---especially if yours is already at 15 feet. "Good on ya' mate "as the Aussies say!
     
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    The "stub" referred to is a parallel conductor radiator.

    Just use insulators to stand it off from the main 33' radiator; however it would be best to also optimize the elevated radials for the other bands as well. 4 radials for "each" band, tuned to resonance, should be sufficient.
     
  8. K0OKS

    K0OKS Ham Member QRZ Page

    I think one of the best ways to test antenna effectiveness is to set it up so you can turn the change off for an A/B comparison and then listen to yourself (even record) on a few of the WebSDR receivers, this tests actual, real world performance rather than limited computer modeling, etc. This is the actual performance we care about.

    Of course you’re need to do the A/B right there back and forth without any delays in between. This way you can tell if it is band conditions, or actual antenna change that are affecting the signals.
     
  9. AI3V

    AI3V Ham Member QRZ Page

    No really, there are way too many places for errors to creep in.

    We work backwards, start with a Marconi in the middle of a large, flat field,

    Put your field strength meter some distance away.

    Start with no "radials", and measure fs and vswr bandwidth and impedance.

    Add radials till there is no improvement.

    In your case, 15 elevated (quarter wave) radials would be enough that adding more won't show much improvement.

    Now, if you install a similar antenna near, say, a house, we know the radials are good to go.

    Rege
     

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