Hi Dave,
In a message dated 96-10-17 12:23:35 EDT, you write:
>I have been reading your discourses on ground losses, near
>fields, far fields, etc. with considerable interest.
I'd pay attention to Eric's post. It's the best and most accurate
explaination of field theory I've seen put into simple terms. (even though I
can't seem to e-mail him direct, hi)
>Question: Does all of this rust in parallel still make a decent ground
>screen?
It's postulation without measurement, but the rust should hurt efficiency
near the antenna base, and very little at the outer ends. I suspect you have
so much surface area it won't make much overall difference.
System loss is the sum of all loss resistances times the square of the
current at every point in the system (NOT at just one point like the
feedpoint). That's why radiation resistance and feedpoint resistance changes
mean so little in estimating efficiency improvements. Unless the system is
very well constructed, a few ohms of loss one way or the other makes very
little difference unless the resistance change is concentrated in a high
current area of the system.
The only way positively determine an efficiency change is by measuring field
strength.
>Aren't there many more little C's than if I had
>used single copper wires?
There is no "C" as such. That is an incomplete represention of what goes on.
The ground system shields the fields (both radiation and induction) from the
lossy dirt, and provides something for the antenna feedpoint to "push
against".
A wide conductor is no better than a thin wire, except as the resistance
drops (but with a lot of radials the current in each one is very low, so the
I^2 R loss is low) and the area between wires "fills in".
>This year I erected 8 copper wire
>elevated radials on top of the rust but don't really see much,
>if any, difference in cracking the pileups. Propagation
>conditions seem to me to be more important than any other
>factor or combination of factors on 160 meters. What do you
>think?
Propagation is always a dominant effect, just watch your S meter. It's hard
to tell from minute to minute what antenna is better if the antennas are at
the same location, let alone comparing an antenna to other systems miles
away. I've measured almost exactly the FS change predicted by Brown, Lewis
and Epstein here, and about a 5 dB shortfall when 60 radials are compared to
4 elevated radials with a full size 1/4 wl vertical. In my opinion, the 60
wires are worth it. To someone else, they may not be.
Here in Georgia, I need all the help I can get on 160. If I was in eastern
Mass, I'd probably be happy with an L with one radial.
>For me 160 is the last and only DX frontier left in 1996.
160's always been that way for me. It's the only band, besides VHF and
higher, where work and knowlege really pay off. That's why it's so friendly,
the people are smarter and more willing to learn or help each other. We can't
get good antennas out of a box.
73 Tom
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