Topband: Measuring field strength

[Tom Rauch]

> those are interesting results. What do you think the 
> systems behave like that?
>    Dave WX7G

Because radials, like antennas, have standing waves on them. 
What we measure at one point doesn't tell us much about 
something some distance away.

A sample of what we measured on 7 MHz shows:

Two radials six feet high. 42 j0                   83dBuV/m
Four radials six feet high  42.5 -j1.6           84.5dBuV/m
Four Buried                 99 +j10.7              81 dBuV/m
16 buried                    58.4 +j15.0 
84.25dBuV/m
32 buried                    53.7 +j15.1            85.75 dB

You can see the base resistance really cannot be used to 
determine FS. Going from two elevated radials to four, FS 
increased 1.5dB while base resistance increased from 42 to 
42.5 ohms. On the other hand 16 buried radials were equal to 
4 elevated radials (within normal signal variation from 
day-to-day) despite the buried radials having 16 ohms higher 
base (feedpoint) resistance.

If I went by base resistance I'd be happy with two elevated 
radials and 42 ohms (but 83dBuV/m). Unfortunately 32 radials 
with ~12 ohms higher feed resistance also has almost 3dB 
more signal. (Keep in mind this is 7MHz and very dry clay, 
where the radials at six feet are effectively pretty high 
compared to 160 meters.) In current measurements the buried 
radials clearly had standing waves.

I'm afraid if we want to know the field strength change we 
just have to measure the field strength change. Nothing else 
works.

It's all a gigantic waste of time and bandwidth if we don't 
measure what we actually want to know.

73 Tom