[ARDF] 80m antenna patterns: Sense v. No Sense...

[Matthew Robbins]

The detail I was missing was that the 2 lobes are out-of-phase. Wow. That
actually makes sense to me now.  (No pun intended, Harley and Karla!)

Matthew

On Thu, May 12, 2011 at 1:28 PM, Jay Hennigan <jay at west.net> wrote:

>  On 5/12/11 10:14 AM, Matthew Robbins wrote:
> > I'm looking for a simple explanation of how a sense antenna works.
> >
> > Does a simple explanation exist? (It's for a presentation, so words or
> > pictures in any combination are okay.)
> >
> > I gave an ARDF presentation the other day, and, although no one asked me,
> I
> > was worried someone was going to ask, "How does that work?"
> >
> > My answer was going to be, "I have no idea."  (I have some vague idea
> that
> > there is an E- and and H-component that are somehow balanced to null one
> of
> > the lobes and produce a one-peak, one-null cardiod pattern.  Or
> something.)
> > If there is no other way, even some equations would be okay.
>
> Nothing special about E and H really.
>
> The two peaks of the loop are out of phase with each other.  The omni
> antenna will be additive with one peak and subtractive with the other
> depending on the wiring of the loop.
>
> The gain of the sense antenna is variable within the front-end of the
> receiver, typically with a trimpot or selected resistor.  It's a
> set-and-forget adjustment, not tweaked during normal operation.  When
> the sense antenna is enabled it is coupled to the receiver input with
> gain equal to that of the loop.  Its signal is equal and opposite of
> that from the out-of-phase side of the loop, which cancels (nulls)
> signals coming from that direction.  It adds to signals coming from the
> in-phase side of the loop resulting in a cardioid pattern.
>
> Matching gain is critical in having an effective sense setup, as is the
> isolation of the sense antenna when it is switched off.
>
> --
> Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
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