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

[Jay Hennigan]

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
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV