From: Jim Weir
Subject: More on HF DF (or ADF)
Date: Mon, 11 Nov 2002 12:38:57 -0800
Organization: RST Engineering
X-Newsreader: Forte Agent 1.92/32.572
There has been some discussion on this NG about how to detect the location of a
transmitter in the HF region (80 and 40 meters is the subject of some interest
here) using everything from a handheld radio's loopstick to a curtain array that
will cover several dozen acres.
Suppose, just suppose I wanted to fix a small, lightweight antenna in a single
position and in some way figure out the direction of a distant signal relative
to some known horizontal axis of the antenna.
In the old days, we would have actually rotated a coil "loop antenna": relative
to a fixed "sense antenna" and driven the motor on the coil to null the combined
cardioid signal of sense added to loop. By measuring the motor's position and
driving a meter in some sort of goniometer arrangement, we could then use the
meter pointer to locate the signal relative to the coil's orientation.
When we did this arrangement, radio receivers were moosey things that glowed in
the dark, and it was far easier to rotate a loop than do all that messy digital
stuff with hot fets.
That is no longer true. A good receiver chip that will amplify and limit the
signal, producing a digital output, is the size of your thumbnail or smaller.
Digital power is a nickel a gigainstruction or thereabouts. At any rate, it
seems to me that there is a better way to DF or ADF (direct bearing readout) on
an HF signal than motors and rotating coils. Ferrites and toroid techniques are
available that we didn't even dream of in the old days.
I've done a fairly exhaustive web search to see if this has been done before
and have come up dry. However, my web search skills are not as honed as some in
this group, I'm sure. Anybody got a pointer to a "how to" article on HF ADF
using a small, fixed antenna?
Jim Weir, VP Eng. RST Eng. WX6RST
A&P, CFI, and other good alphabet soup