Topband: Long Path Direction!]

[Tom Rauch]

Those are all very good questions Ken.

> What is the half power beamwidth of the most directive antenna that any
> of you have for receiving on 160 meters? What about the half power
> beamwidth of the most directive rotatable antenna that you have?

My receiving antennas are typically about 40-50 degree half power beamwidth.
Since I have multiple wide spaced arrays I can, through calibrated phasing,
resolve less than 10 degree heading variations without much effort. It can
be less than that if I have some known reference sources to calibrate from.

Without large array phasing, I can quickly and easily tell within 22 degrees
the direction of signal arrival. For example I can tell WSW from SW or W by
just using my array of verticals.

I'm sure K9DX can resolve close enough to know NNW from NW, and I'd bet
several others can also (N7JW also comes to mind).  With a single Beverage
group or a broad pattern antenna like two Beverages spaced 200 feet, you can
almost certainly only tell heading within 40-50  degrees no matter how many
directions you have because HPBW is too wide.

> You may know which beverage the signal is strongest on, which may tell
> you approximately which direction it is coming from. But then the exact
> directional pattern of your beverage is unknown. Sure, you can predict
> what it ought to be using modeling programs.

For single Beverages or close spaced Beverages, I agree. But patterns are
quite predictable when the antennas are in the open and are large arrays of
simple non-critical elements.

>I haven't read any
> discussion here about having a helicopter with a signal generator flying
> around several miles from your QTH to measure the actual pattern of your >
antenna, so you don't really know for certain what the pattern is.

I have a pinger that beeps on 1843. When I started installing antennas years
ago, I checked the expected groundwave nulls and they always agreed within
my ability to measure angles (about 1 degree). The only exception was when I
made a mistake in layout or phase, and they have been traceable errors.

> If you have a rotatable directional antenna, you might be able to
> resolve the direction that the signal is coming from to within perhaps
> several degrees. If you use the null of a loop, that would probably be
> the most precise way to determine the direction, but not on a weak
> signal that you can barely receive.

Single loops won't work well at all for skywave DFing not for the reasons
you mentioned, but also because there is too much multipath and scattering.
The null is too sharp, and the response too broad. They are also very
difficult to decouple from feedlines and are heavily influenced by
surroundings. Single loops are almost useless for skywave DFing.

The only reliable way to resolve directions of weak skywave signals is with
large arrays having a narrow clean response, or by measuring phase
differences in multiple small arrays with wide spacing.

73 Tom