Re: http://www.mfjenterprises.com/products.php?prodid=MFJ-1026 - Whaddya think?

RHF wrote:

RH,

"If you combine a loop and a whip, you can co-locate
them and dispense with the separation entirely."

Can you expand on this statement - please ~ RHF
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The magnetic field lags the electric field by 90 degrees and
so you can determine from which of two opposite directions a
wave is coming by comparing electric and magnetic fields.

In particular, you can cancel one and peak the other, by taking
the electric field off a whip and the magnetic field off a loop
and combining them, the whip and the loop being in the same location.

In practice, you don't do any analysis and just null out the station
you want to null out.

To do the same thing with two whips requires some separation of the
antennas, a quarter wave being best.

(Smaller separations start to reduce the gain in un-nulled directions,
and larger separations start to lose coherence when there's a spread
in angles of arrival from the nulled station. Neither is fatal, but
just a reason to prefer a quarter wave separation. The loop + whip
eliminates the problem completely by preferring no separation at all.)

``Lags'' by the way is a matter of convention, you can as easily say
``leads,'' all depending on whether you like right-handed or left-handed
coordinate systems. They're 90 degrees apart, is all. A phasing
system like the ANC-4 puts the 90 degrees back in one path so one
signal can be used to cancel the other completely.

The reason, by the way, that the depth of nulls is limited in
casually-constructed single loop antennas is that they pick up a little
eletric field along with the magnetic field, and there's no orientation
that nulls both eletric and magnetic fields at once. If it were
a matter of only the magnetic field, there would always be some
orientation that nulls it exactly and completely, no matter how
sloppily constructed the loop is, because the magnetic field can
always be used to cancel itself somewhere.

Another by the way : the reason I started adding antennas and ANC-4's
was to null out multiple stations. Say you want to get rid of two
MW local broadcasters, A and B, to receive C, on the same frequency.

Step 1. Null away A using antennas 1 and 2.

Step 2. Null away A using antennas 3 and 4.

Step 3. Null away B by combining the outputs of step 1. and step 2.
Station A is also nulled because it's not present in the inputs.

Step 4. You're left listening to C, the station you wanted.

You can also do this with only 3 antennas and 2 ANC-4's but there's no
simple procedure I know of to follow to achieve it beyond endless
fiddling until it's done.

And of course with 8 antennas and 7 ANC-4's you can procedurally null
3 stations and receive a fourth, though I never got this to work.
(Or, if you had a computer to do it, you could do it with
4 antennas and 3 ANC-4's, showing that my regularized method is
unnecessarily exponential when you start adding nulls.)

--
Ron Hardin
rhhardin@xxxxxxxxxxxxxx

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