TopBand: Split Gorunds for Folded Feed Verticals?

[w8jitom@postoffice.worldnet.att.net]

Hi Jim,

I expect this thread to be censored at any moment, but hopefully we 
can come to some resolution. I think understanding HOW antenna's work 
is very important to 160 operators. It's the last band where you find 
so many antenna experimenters.

> Anyway, I had a half baked idea that occurred to me when I previously used
> folded feed antennas. (I didn't use them for improved efficiency, but that
> is another story) I realize that the ground losses are the same for a
> folded antenna as for a monopole of the same height when connected to the
> same ground.

That statement is precisely correct. Nice way to word it.

> Is the same true if I use an electrically isolated ground for
> each fold? That is, instead of tieing the drop to the same ground the
> feeder is tied to, tie it to a separate ground (or set of radials). 

In specials cases efficiency can be improved. The case rules are each 
ground must be very small electrically and the antenna must be very 
short, and earth itself must be the primary ground. That is why the 
method you describe is common on VLF, but NOT common on MW and HF.

On VLF, both the ground and radiator are fractional wavelengths 
physically. In that case parallelling multiple drop wires spreads the 
VERY high currents out in several small ground systems. Cut the 
current in half in each ground system, and losses drop by four.

Unfortunately that only works when the ground systems are very 
dependent on the earth connection (VLF), the antenna is very short, 
and the actual ground system area is very limited.

It's more like three ground rods are better than one and keeping 
the high current path from the very short radiator vertical 
(instead of stretched along the ground) than anything else.

> would be easiest with an elevated feed of course, but then ground losses
> are lower in that case anyway. Or would the ground losses be the same (as
> for the separate case) if I just tied both grounds together and fed the
> folded antenna against it?

I suspect the latter is the case, you would have the same thing. Now 
if you could have no long radials, and your 160 antenna was five feet 
tall, the multiple drop and ground system might work.

But all things considered, isn't a simple system of twenty or more 
1/8 wl or longer radials easier?

73 Tom

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