Ground mounted Vertical radials

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by M0WZD, Oct 10, 2014.

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  1. M0WZD

    M0WZD Ham Member QRZ Page

    Hi all

    I have a Hy-Gain 18AVT 5 band vertical, in the manual (link at bottom)
    it only mentions using radials when it is roof mounted, there is no
    mention of radials for ground mounting, also in the manual it has
    a radial pattern for when its roof mounted but the antenna is
    mounted in a small plot so I cant work to that pattern.

    The plot the Antenna is in the middle of a 17m x 3.6m plot

    So I am looking for advice on what length and how many radials to use,
    another thought I had was I could lay out some chicken wire fence and pretty
    much cover the grass under the Hy-Gain
    would that be better than wires ?

    And lastly does it matter what kind of wire I use for radials ?
    was thinking something like this
    http://www.ebay.co.uk/itm/100M-ROLL-OF-1-2-PVC-COATED-GARDEN-WIRE-GENERAL-PURPOSE-/331326211870?pt=LH_DefaultDomain_3&hash=item4d2494c71e

    PA100127.JPG
    http://www.drop22.com/hygain_18avt_antenna.pdf
     
  2. W6OGC

    W6OGC Ham Member QRZ Page

  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I don't think the 18AVT is a current model.

    However in the instructions for the 18AVQ (80 through 10m vertical), it says...

    Installation of Radials
    There is no need to make radials exactly ¼
    wavelength long for the 18AVQII. In fact, the only
    case where you should have ¼ wavelength radials
    would be for approximately 90 radials. This differs
    rather dramatically from the case of the elevated
    antenna where resonant radials are installed above
    ground. Since the radials of a ground-mounted
    vertical are actually on, if not in, the ground, they
    are coupled by capacitance or conduction to the
    ground, thus resonance effects are not important.
    Basically, the function of radials is to provide a
    low-loss return path for ground currents. The reason
    that short radials are sufficient when few are used,
    is that at the perimeter of the circle to which the
    ground system extends, the radials are sufficiently
    spread apart. Most of the return currents are already
    in the ground between the radials rather than in the
    radials themselves. As more radials are added, the
    spaces between them are reduced and longer lengths
    help to provide a path for currents still farther out.
    Since the 18AVQII is a multi-band, vertical
    antenna, the radial system should be optimized for
    the lowest frequency you plan to use. Higher
    frequencies will benefit equally from the ground
    system, while lower frequencies will not show as
    much improvement.
    To determine the optimum radial installation for
    your 18AVQII, you must first decide what the
    limiting factor for your installation will be. The list
    below includes factors that need to be considered.
    1. Cost of radial wires
    2. Area available for radials
    3. Efficiency of your antenna
    Use figure 1 below to design a radial system to the
    optimum length for your preferred operating band.
     
  4. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    Due to limitations of my smartphone, I cant really determine where the actual feed point is. It looks like the antenna may be mounted on a pole. Just to clarify just in case, "ground mounted vertical" means the feed point is close to the ground.

    The secondary pole (if metal) in the picture is mounted too close to your vertical and will most likely skew the radiation pattern and may affect your tuning and/or swr readings.

    Radials should be as long as the antenna is high. They should extend in an equally spaced pattern around the base of the antenna (if ground mounted) and should not be buried below the surface any deeper below the soil than it is physically necessary to conceal them. It is not actually required to bury them at all but doing so may protect and preserve the radials from damage.

    120 radials is what is considered as the optimal number of radials for all ground mounted vertical antennas. However, this is not always realistic to achieve. I would suggest 16 radials as the absolute minimum, 32 as a matter of achieving acceptable performance, and 64 radials if you should desire better than average performance from your antenna.

    Individual copper wire radials will achieve the best results. The wire can be#bare or have a protective sheath covering, it doesn't matter. Chicken wire is not adviseable because most of it will rust away and disintegrate in a year and you will experience degraded performance.
     
  5. KM1H

    KM1H Ham Member QRZ Page

    With your property limitations the ony real method to mask/minimize ground losses is to install a full galvanized metal mesh in that area.

    The usual chicken wire is simply twisted together and once corrosion sets in you will have a thousand + diodes radiating RF.

    The following link (representative of what is economical over here) has welded junctions and then galvanized and if you paint both sides with a nice green latex paint it will last a long time; use a roller on both sides. The galvanizing takes solder very well so it is easy to connect several copper wires to a ground ring of 8 gauge or larger (US size, dont know UK equivalents) copper wire around the base of the vertical. Also install a copper plated ground rod or copper pipe for lightning protection and connect that to the copper ring. For static pulses and nearby lightning discharges you can wind a 50uH choke from #16 or so wire and connect between the antenna and ground.

    A sleeve/current balun over the coax at the feed will reduce neighborhood electronic noise from that densely packed area.

    Id run several parallel runs length wise to fill the available area and wire together every 12" or so.
    This will be far more effective than any attempt at duplicating in copper wire...unless it is free.

    Ive used similar but heavier galvanized and plastic coated "rabbit fence" for 80 and 160M verticals for decades that is still fully servicable. But US made is very expensive here these days and the Chinese stuff is what most stores carry and the plastic coated is usually not galvanized. This link is the thinner gauge Chinese.

    http://www.lowes.com/ProductDisplay...gId=10051&cmRelshp=req&rel=nofollow&cId=PDIO1

    Good luck

    Carl
     
  6. WB8NQW

    WB8NQW Ham Member QRZ Page

    Many years ago I had the 18AVQ vertical which I loved. Without radials I thought it worked quite well. The mounting pipe was probably 3-4 feet deep. Local soil is not sand but good hard clay as we were part of the Great Black Swamp in the 1800s. Now I have the 18HT-JR with 39 radials most of which are 40 feet long with some shorter due to patio and sidewalks.

    73
    Bob
     
  7. K8JD

    K8JD Ham Member QRZ Page

    Why 120 ?

    I keep hearing this 120 radial idea pounded upon.
    This is a carry over from the AM broadcast industry where the life blood of the business is the ground wave coverage of the primary service area. This is the number of radials to insure a known and unchanging performance of the antenna over all 4 seasons and rain snow or sunshine. This is even more important to a directional antenna where changing conditions of the ground can cause pattern shifts and interference to other stations sharing the freq and guaranteed protection from this transmitter.
    I have read that a maximum 60 radials and sometimes even a lot fewer is fine to get a good sky wave signal (actual ground wave is not a factor in Amateur Radio communications) out of an HF Amateur band vertical mounted on the ground.
    3 or 4 Resonant Radials per band is sufficient for a roof mounted vertical to perform well, More is not going to make much difference for a roof mount.

     
    Last edited: Oct 10, 2014
  8. KH6AQ

    KH6AQ Ham Member QRZ Page

    A couple dozen random length radials covering the 17 x 3.6 meter plot will be fine. The wire listed doesn't say what it's made of. For long life copper wire should be used, either insulated or bare. I like to use #14 AWG stranded house wire because it's easy to work with. I staple it to the lawn (mow it really short) using plastic lawn staples. DX Engineering sells them. I let the grass grow 3" high then mow it on the highest setting. The radials seem to sink into the lawn after a few months.
     
  9. N0FN

    N0FN Ham Member QRZ Page

    Reference for why 32 radials is plenty: http://www.antennasbyn6lf.com/design_of_radial_ground_systems/, particularly Figure 1 of http://rudys.typepad.com/files/qex-ground-systems-part-3.pdf

    -Neil KD0UKC
     
  10. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I didn't just re-read Rudy's stuff, but I've read it before (long ago) and it's worthwhile.

    I did some experimenting with ground radials for HF at a property in upstate NY where we had about 70 acres to play with (not mine, it was a friend's grandmother's farm and we operated 160m contests from there in the early 80s) and found the longer you make the radials, the more you need. Kind of counterintuitive. Also, if you can make the radials REALLY long (like 5 wavelengths) they fall outside the Fresnel zone and start to impact takeoff angle quite a bit...the longer, the better for that...but if you do that you need a whole lot of them or the radial ends will be too far apart.

    We ended up with 100 radials each about 1000' long (free wire, it was #16 AWG solid copper from a surplus house who donated ten 10K' spools to the cause if we picked them up) and tried the "connect/disconnect" trick. That's where you bring ALL the radials at the monopole end to a common tie point connected to a HUGE instant disconnect. We used a battery jumper cable clamp, solid copper rated a few hundred amperes with a strong spring, capable of making very low-resistance contact to the grounding plate at the feedpoint.

    That's a real eye-opener! I remember at about 9 PM local we tuned in ON4UN on 160CW (ARRL 160 contest) and he was about S9. Sent someone outside into the field to "undo the clamp" thus removing the radial system. We tried this on and off about five times. Every time we disconnected the radials UN's signal dropped from S9 and rock solid to about S2 and quite noisy, difficult copy. Clamp them on again, back up to S9. Two different receivers (neither necessarily calibrated), a KWM-380 and a TR-7 (modern rigs at the time), and both agreed within a couple of dB.

    The theory (and verifying models) that radials improve performance by "3 dB" is, um...not duplicated by real-work experiments as far as I can tell.
     
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