Robert11 wrote:
Hi,

Have finally gotten back into hobby, now that I am retired.

Have been reading the ARRL books, a bit, again, and realize I'm still quite
confused over the antenna pattern diagrams they show for the various types.

a. What is plotted in these diagrams; the H field, the E field, or the
resultant of the two ?

Either one. Once you get more than a fraction of a wavelength from an
antenna, the E and H fields are in a fixed ratio (E/H = 377 ohms). So
plots of the two are identical, except for the 377 ohm scale factor. The
pattern is more often expressed in dB relative to some reference (most
often to an isotropic source, expressed as dBi). This numerical value is
then the E field, H field, or power density far from the antenna
relative to the reference. The pattern shape and dBi value of all three
are the same.

b. When they talk about field strength, what do they mean ? Again, the H
field, or... ?

Field strength technically means either the E field (in volts/meter) or
H field (in amps/meter) but, as I said above, once you know one you can
easily calculate the other unless you're very close to the antenna.
Pattern plots are nearly always for the far field, where E and H have a
fixed ratio and the pattern shape is the same regardless of distance. In
the near field (which isn't of any interest for your application), the
pattern is different for each distance, and the ratio of E to H isn't
fixed. Therefore, near field data are usually given in tabular form.


c. Have a receive-only antenna running around the 4 sides of my attic. Open
at the end.
Should I tie the end to the beginning, making a horizontal loop up
there, or not ?
Why ?

Tying the end might change the pattern enough to make a difference in
your ability to receive, depending on the directions of the signals you
want to hear and of incoming noise. There's no single answer for
everyone. You'll simply have to grit your teeth and experiment.

d. Do listening only, from 0 to 30 MHz, and from all compass points.

Would a straight run of wire along one side (thus foresaking the
lengths provided by the other 3 sides)
gain me anything, or is the square loop configuration probably the best
overall compromise
for pulling stuff in ?

See the above answer.


e. Tried to find some but couldn't.
Any pix/diagrams on the web showing the lobe patterns as a function of
frequency for:

a single random-length wire
a 4 sided loop, open at the end, like I now am using
a 4 sided loop, closed at the end

There are a number of free antenna modeling programs that will help you
answer your questions. Just keep in mind that for HF receiving, gain in
the desired direction is of no consequence by itself. The only thing
that will help you receive better is to have a pattern that has more
gain in the direction(s) of the desired signals than in the direction(s)
which noise comes from. If the signal and noise come from the same
direction, there's nothing you can do to improve your ability to hear
signals. In that case, more gain will make both the signal and the noise
louder in the same proportion. You can get the same effect a whole lot
easier by turning up the volume control.

Roy Lewallen, W7EL