[TowerTalk] re Radials

[hasan schiers]

Dave,

If you are going to lay the radials on the ground and the vertical is ground mounted, then I think you would be very happy with the moderate performance of 16 radials, 1/4 wave or so on the lowest band. There is NO RESONANCE effect for radials that are on the ground or shallowly buried. If you elevate the radials they must be individually tuned for a 1/4w for each band.

The spec for 3 on each band, at 1/4 wave long implies the antenna is NOT going to be ground mounted, but rather will be supported a significant distance in the air, thus becoming a "ground plane" antenna. Your performance with 3 tuned elevated radials on each band should be "decent", although far from ideal. The primary variable for elevated radials is how high! The higher you get the antenna as a portion of a wavelength, the more efficient your elevated tuned radials become. If you get up 20 to 25' on 40m, the performance can be quite good. On 80m it won't be as good. 

Let's not get overly lost in the Take Off Angle (TOA), commonly called angle of radiation. The key is how much power is put into the lobe of radiation centered at the TOA, not the TOA itself. The reason I say it this way is if you have very high ground return losses (poor radial field), your TOA will still be low...but there will be very little power going into that TOA because it has been eaten up with ground losses.

For this reason, a lot of people opt for the elevated ground plane with tuned radials. The mistake they make, however, it not getting the base of the elevated vertical high enough to cause the tuned elevated radials to "mask" the high losses of the earth beneath it. 

Again, for what you are talking about (moderate operational success, as opposed to ideal), 3 tuned radials per band with a height of 15' might work out just fine especially on 40m and 20m. The nice thing is, you can always add more!

73,

...hasan, N0AN


  ----- Original Message ----- 
  From: Dave Tipton 
  To: Jim Lux ; hasan schiers ; Bill Coleman ; Dave Tipton 
  Cc: towertalk at contesting.com 
  Sent: Friday, June 16, 2006 12:16 PM
  Subject: Re: [TowerTalk] re Radials


  Well.. I have an old 5BTV (Hustler) that I'm going to put up this weekend...  It is spec'd for 1/4 wave radials on each band, telling me that I need to have 3 on each band...

  MY question...  If I were to lay down 8 radials on 80, 80 on 40 and 8 on 20 (The only 3 bands I'm really interested in), do you think this would give me sufficient performance to rely on it for some medium distance work?  I'm not going for big DX here, but I'd take it if I heard it.. I now have an 800 watt amp in the mix too, so I'm going for as near resonant as I can get.

  Dave

  Jim Lux <jimlux at earthlink.net> wrote:
    At 06:52 AM 6/16/2006, hasan schiers wrote:
    >Actually, they can be MUCH shorter than .22 wl, as long as you have enough
    >of them. Many more shorter is quite a bit better than many fewer longer.
    >
    >There are free programs by G4FGQ, RADIAL2 is the name I think, but just
    >google G4FGQ and you will get to his site and free downloads. The radial
    >program is a good one and answers all the questions being raised. It lets
    >you manipulate number/length/freq and ground characteristics to show
    >efficiency. VERY HANDY!


    Except that Reg's program isn't necessarily a very good model of 
    radials. He's modeling the radial field as a bunch of lossy transmission 
    lines (which is sort of fine), but doesn't account for the transfer of 
    energy into the surrounding soil, some of which reradiates, as opposed to 
    being simply loss in an equivalent loss resistance. Reg has some 
    explanation of what he's doing in the notes in the program, but doesn't 
    publish his algorithms or source code, so it's tough to figure exactly what 
    he's doing (and I'm not patient enough to just run lots of cases and 
    reverse engineer it). It's also not clear how Reg is modeling wires close 
    to the surface, where a significant part of the field crosses the 
    ground/air boundary.

    That said, it might be a handy way to tinker around and gain some 
    understanding of the effect of various radials.

    If you really, really want to model radials, you're probably best off to 
    fork out the bucks for a copy of NEC4 and do it right. (NEC4 does model 
    buried wires, and has been rigorously validated, and all the gory details 
    are published) Otherwise, just use the "throw lots of wire out, don't worry 
    about the exact length, and more radials is better than fewer" approach.

    Jim




    >The data I got is completely consistent with the ARRL publications that
    >describe how to get minimum loss for a given wire length available, as well
    >as with G4FGQ's program. I do think Reg's program is a bit optimistic, but
    >it points one in the right direction. I have full faith in the studies
    >published in the ARRL Antenna Handbook on how to optimize a radial field, as
    >my actual measurements agree very strongly with the article.