N9NEO wrote:
1) I understand that the common method to couple a portable radio to
the loop is to just stick the radio into the center of the loop.
Doesn't this method then tend to have directivity in two orthagonal
directions? In other words the loop will have a node in the North-South
direction while the ferrite rod will tend to be directive in the
East-West direction, because of the orientation of the ferrite rod
within to the Loop. So now the nice null that you have along the axis
of the loop is destroyed because the ferrite is aligned there. Is this
correct? Maybe it might be good to couple signal in another fashion.

Every small antenna arrangement responds identically, and has the same null
and peaks. Two loops simply function as a single loop oriented in some
other direction.

The complication is that there are two signals out there, the electric field
and the magnetic field. Loops respond mostly to the magnetic field, and
have an infinitely deep null for the magnetic field. They also respond
somewhat weakly to the electric field, and it's the electric field response
that ``fills in'' the infinitely deep nulls. The careful construction of
loops is to, by balancing things out, try to eliminate as much electric field
response as possible. The depth of the magnetic field null is already
infinite and is unaffected by careful construction.

The reason the E and M fields don't combine like two M fields into a single
antenna's response is that they're 90 degrees out of phase, and so can never
cancel each other by reorienting the antenna.

Whips have a null at endfire that's similarly infinitely deep, except for
magnetic field response filling _it_ in.

--
Ron Hardin


On the internet, nobody knows you're a jerk.