From: email@example.com (Tom Bruhns)
Subject: Re: More on HF DF (or ADF)
Date: 12 Nov 2002 10:26:17 -0800
NNTP-Posting-Date: 12 Nov 2002 18:26:17 GMT
I recently had a look at a commercial RDF antenna that was an
appropriate size to put on a small airplane, if you wanted. It
covered all of HF and some above. I'm quite sure it's available to
anyone who wants to pay for it, though I suppose most of the people
who buy them do so with taxpayer money. As I recall, the antenna
structure itself was described as "annular slot". I was surprised by
its accuracy, though didn't have a chance to test it with as many
"real" signals as I might have liked.
Jim Weir wrote in message news:...
> 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