Topband: beverage lobes

[Michael Tope]

----- Original Message ----- 
From: "Larry Molitor" <w7iuv at yahoo.com>

>
>>>>Maybe in GA. I can say for certain here in the WA desert it does a lot!
>
> In an ideal perfect-phase lossless world ........I'm not going to argue 
> theory. I happen to agree with the theoretical case as you presented it. 
> However that does not account for the fact that I can really see a 
> dramatic difference in performance with the longer Beverages installed 
> here. Since I make the observations on real topband signals and A/B switch 
> around the various wires I can only assume that there is a difference 
> between the theoretical case and my practical installation that has not 
> yet been accounted for. When the model does not agree with the measured 
> results, either the model is wrong or the measurement is wrong. Since the 
> measurement is copy/no copy and is repeatable, there must be an 
> inconsistency in the model.
>
> The results have been consistent for the several years I have been up here 
> in WA with many acres to play with. The differences are way more than 
> enough to make the extra effort of installing long wires worth it. I 
> guarantee that I would not be walking all those extra miles across plowed 
> fields unless I was getting something out of it. I agree that phased wires 
> would probably be better but in my particular situation I cannot keep the 
> phasing coax's intact for sufficient time  to make good observations. What 
> little I have done with phased systems was promising but pointless if I 
> can't keep coax on them.
>
> All of my wires are 8 foot high maximum and most are 30 inches high. All 
> are terminated identically with 8 ea. 6 foot long wires on the surface or 
> buried about 1 inch with a single 3 foot ground rod in the center. Most of 
> the wires have to be removed periodically for farming activities hence the 
> minimal grounds. I use galvanized 17 gauge fence wire. I tried good copper 
> once and could not measure any difference at all nor see any difference in 
> on-the-air performance. This season I was limited to two short wires due 
> to the farm stuff. With a little luck, I'll be able to put up 8 or 10 more 
> next season. I plan on running out at least one 2000 footer. At this point 
> I have no idea if it will be worth the effort but it will be fun to try.
>
> 73,
>
> Larry - W7IUV
> DN07dg - central WA
> http://w7iuv.com
>


I think the fly in the ointment on this debate could be ground
conductivity. A beverage looks more or less like 1/2 of a 2
wire transmission line over a ground plane with the 2nd half
of the transmission line replaced by the ground image. If the
ground conductivity were very high, then I would expect that
the loss/unit length would be low and hence the current taper
would tend to be very gradual. Conversely with poor
conductivity, I would expect a more rapid current taper. The
dielectric constant of the ground adds yet another dimension
to this problem. Thus, what's true in one location, may not be
true in another location with very different ground conditions.

As a practical matter, I would settle for enough room for a
300' beverage, but that's another story.

73, Mike W4EF..............................