AM-rated ground radials

Discussion in 'Amplitude Modulation - AM Fans' started by WA3VJB, Feb 26, 2018.

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  1. WA3VJB

    WA3VJB Ham Member QRZ Page

    Was talking this weekend with Gary, W2INR about the merits of "digital" TV antennas, and oxygen-free speaker wire, and I now have begun exploring AM-rated ground radials made of Aluminum electric fence wire. Besides its special AM ability, I wonder if anyone has first-hand experience with how bare aluminum wire withstands ground burial in soil that ranges toward acidic from organic compost, like out in the woods.

    Chemical properties look pretty good for the money. It has about 60 percent conductivity compared with copper, and is said to have good resistance to corrosion once it gets a surface coat of oxide. I've had some aluminum jacketed, semi-rigid hardline out in the back yard for more than 20 years, and its main deterioration has come from squirrels gnawing on it rather than exposure to the elements.

    Another concern is whether I should avoid using a stainless steel ground radial plate because of the risk of galvanic corrosion against aluminum. I know from boating that they use aluminum and zinc as sacrificial anodes to protect steel & stainless steel components in the engine and outdrive. But that presumes immersion in brackish saltwater around here that makes a far more dandy electrolyte than wet soil. Various hits from internet searches recommend using other methods to mount the wires, like copper buss bar, drilled copper pipe, anything BUT an aluminum plate drilled to bolt aluminum ground radial wires.

    Chief problem seems to be corrosion between the mounting bolts the plate and the wires, where the oxide that naturally forms on the aluminum becomes an issue in an RF environment.

    Wat say, over, over.

    Attached Files:

  2. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    SS and aluminum are not bad for galvanic corrosion. SS screws are used in aviation. Use some oxygen excluding compound like GB Gard, which is conductive, or various other compounds typically used with antennas.

    I wouldn't recommend using Al wire due to the higher losses and increased susceptibility to corrosion. If you have free wire and if maximum performance and longevity over perhaps a decade is not an issue, have at it. b.
    WA3VJB likes this.
  3. W7TFO

    W7TFO Subscriber QRZ Page

    No more than 12 radials or you'll never QSY without a 'wacky-match'.

    I learned that the hard way.

    WA3VJB likes this.
  4. WA1QIX

    WA1QIX Ham Member QRZ Page

    I use #11 aluminum electric fence wire for my ground system which consists of 120 1/2 wave (each is about 125 feet long) radials fanning out from the tower in all directions, which are not buried, but just lie on the ground (the antenna is way out in the woods). So far, so good. It's been in more than 10 years.

    The addition of the ground system made a very noticeable difference in the consistency of the antenna's performance over seasons - particularly during the summer when the soil under the antenna (at the top of a somewhat rocky hill) dries out and ground reflectivity is poor at that point. The background noise level is essentially non-existent.
  5. WA3VJB

    WA3VJB Ham Member QRZ Page

    What are you using as a tie point for the radials?
    Plate material, hardware, protective coating, if any.
  6. K9STH

    K9STH Ham Member Staff Member QRZ Page

    At least around here, within a year, or 2 at most, buried aluminum wire basically "disappears" due to corrosion.

    A while back, a certain amateur radio operator installed a HyGain HyTower in his large back yard. Wanting to provide the "optimum" buried radial field, he decided to install the 120 radials that are normally used for AM broadcast stations. However, to reduce costs, he used aluminum wire. In fact, he borrowed the manual sidewalk edging tool that I had modified to cut deeper slots, in the soil, that I had used when I installed the about 48-buried radials that were used with my HyTower.

    For several months, the HyTower worked very well. But, as time went on, the performance seemed to be decreasing until the performance was absolutely lousy. Finally, he went out and started going over everything associated with the antenna. He checked the feedline including the connections to the antenna and the grounding system. He checked all the hardware holding the tower sections together and made sure that there was no corrosion where the tower sections overlapped. He even climbed the tower to insure that the connection between the wire, that runs from the bottom of the antenna and the tubing above the tower sections, was still in good shape. And a lot of other things.

    Finally, he started pulling on the wires that formed the buried radials. To his dismay, in most cases, there was less than 2-feet of wire left intact! The longest was less than 5-feet. Basically, the wire had disappeared into the soil. Frankly, he was heartbroken. He did replace the radial system but installed 48-buried radials using copper wire instead of aluminum.

    Others, in this area, northern Texas, have had the same experience with aluminum wire used for buried radials. Now, the ground conductivity, in this area, is the best in the entire 50-states which definitely helps with antenna performance.

    Glen, K9STH
  7. AC0OB

    AC0OB Subscriber QRZ Page

    I agree and this has been my experience as well.

    Aluminum wire turns into an, "ASH" is the best way I can describe it.

    Here is what I use and it is still there.

    Available on 2000 foot spools (approx. 25 pounds)
    or by-the-foot.
    Per foot: $0.25

    2000 Ft. Spool: $189.00 [​IMG]

    Soft-Drawn 14 AWG Copper Wire [​IMG]
    4,110 Circular Mils Diameter: 0.064 in.
    Weight: 12.4 lbs/1000ft.

    Dig a trench with an edger and stake the wire down with this:

    For the radial "ring" I use #6 bare solid, cut into a 38" length.

    I bend the wire into a circle and bend the ends down to make two, 8" spikes. Those spike ends are driven into the soil.

    Radials are then silver soldered to the radial ring. I also take an 18" length of #6 wire and go from the radial ring to the ground of my tuning box at the base.


    Attached Files:

    Last edited: Feb 26, 2018
  8. K4KYV

    K4KYV Subscriber QRZ Page

    Silver soldering is a MUST. For my first radial system, many years ago with an inverted-L made of TV push-up masts, I used regular lead/tin solder to solder the radials to a copper ring round the insulated base of the vertical. The solder was even worse than the aluminium radial wires in STH's friend's ground system. Within only a few weeks, the solder turned to a white powder and the radial wires literally fell of the copper ring. That became a routine as long as I had that system, to go out about once a month with propane torch and roll of solder, and re-solder the radials to the ring.

    When I put in my present system in 1983, I used the 15% silver alloy sticks plumbers use, and to-day they are still just as good as new. Although not dirt cheap, those silver alloy sticks are not outrageously expensive either, because they are sold in quantity to plumbers. Plumbing codes now prohibit regular lead solder for two reasons: (1) for the same reason I observed with my radials; minerals in the water react with lead solder, turn it to white powder and the pipe connection eventually starts leaking. (2) Fear that lead in the solder would leach into and contaminate drinking water.

    It takes more heat to melt the silver alloy than a regular propane torch will deliver. I used what is called MAPP gas, which would heat the copper to a dull red. Once the silver alloy is fully melted to a liquid, copper soaks it up like a sponge soaks water. No flux is necessary nor is there any need to clean the copper to a shine; just brush away any loose scaly stuff and the torch flame burns off the rest and you see bright copper. One precaution is to be careful and not melt the copper wire. My radials are made of #12 soft-drawn, and a couple of times I melted the copper wire to a blob of copper on the end while trying to braze. Luckily there was enough slack that I was able to pull on the radial and get enough wire to make the connection.

    The last time I checked, real MAPP gas had been discontinued. They still sell stuff in the bright yellow cannister, but I noticed that the name is now MAP gas (with one P). I haven't tried to use it, but I was told by someone recently that it isn't as good as the old stuff (a familiar story), that it doesn't get much hotter than does a regular propane torch.

    I would avoid those over-priced Hammy Hambone radial plates that use screws to attach the wires, except maybe for a temporary set-up like you use on Field Day. Most likely, the screw connection will eventually loosen up or corrode and leave a flaky connection. A connection brazed with silver alloy solder / brazing rods will last as long as the copper wire itself.
  9. WA1QIX

    WA1QIX Ham Member QRZ Page

    I use large split bolts to connect all of the radials together.

    Remember, this is NOT a ground system for a vertical, where there is a lot of current. This is a ground system under a dipole, where ground reflection is the most important thing. I don't know how much actual current flows through the radials, but their presence in great numbers makes a difference in the performance of the antenna.
  10. K4KYV

    K4KYV Subscriber QRZ Page

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