On 19 Jul 2011 20:55:42 GMT, Allodoxaphobia
wrote:

In BCB SWLing you want the null(s) deep (and steerable)
to kill the strong, unwanted station.

This characteristic demands the SAME considerations as required for a
sharp beam of high directionality.

If we were to select the antenna that matches your quoted specs above,
it would be called the Cardiod (example available in EZNEC). Problem
there is the 30dB null isn't steerable (not enough elements). And it
is large (too large for the back yard):
1. Too tall for most to build.
2. Elements too far apart (out of necessity for, dare I say it?
Phasing).

As it is designed as a transmit antenna, too tall is quickly
dismissed. You can use as short of one as proves useful.

The first element, now being shorter, also allows us to add any number
of shorter elements in an array around (or mixed in with) the first.
This brings steerability. The more elements, the better angle
resolution and null depth control.

You can pull the additional elements (if only one more to build a
proof of concept Cardiod) closer to the first (dismissing the large
spacing objection), and introduce the necessary time/phase control
through:
1. cabling;
2. analog delay circuits;
3. digital delay circuits.

Moving to a digital solution controls all variables.

If none of this is covered in the "Dallas Files," it would be best to
leave them in the File Cabinet. Jim has provided adequate links to
fill in the gaps and no one was injured in the process of obtaining
the information.

73's
Richard Clark, KB7QHC

On 7/19/2011 3:47 PM, Richard Clark wrote:
On 19 Jul 2011 20:55:42 GMT, Allodoxaphobia
wrote:

In BCB SWLing you want the null(s) deep (and steerable)
to kill the strong, unwanted station.

This characteristic demands the SAME considerations as required for a
sharp beam of high directionality.


Actually, no.
You can form a deep null with a much simpler antenna system than for
high directionality.

All you need is to "cancel" the signal from the undesired direction.

If you had two verticals spaced some distance apart, fed by equal length
transmission lines, and one is polarity reversed, you get a fairly sharp
null on the line perpendicular to the line between the antennas.
(e.g. a signal coming from broadside will exactly cancel in the combining)

A loopstick antenna on a ferrite core or a multiturn loop, as popular in
direction finding, is another example with a fairly sharp null.



Now.. if you want one null, and one null only, that gets a bit trickier
in a small space. I don't know that you can do it with only two
elements (haven't thought about it much).

And if you want to steer the null.

One traditional approach in direction finding is to use a goniometer or
an adcock array.


If we were to select the antenna that matches your quoted specs above,
it would be called the Cardiod (example available in EZNEC). Problem
there is the 30dB null isn't steerable (not enough elements). And it
is large (too large for the back yard):
1. Too tall for most to build.
2. Elements too far apart (out of necessity for, dare I say it?
Phasing).

that's the "one null and one null only" problem.

On Tue, 19 Jul 2011 17:45:01 -0700, Jim Lux
wrote:

On 7/19/2011 3:47 PM, Richard Clark wrote:
On 19 Jul 2011 20:55:42 GMT, Allodoxaphobia
wrote:

In BCB SWLing you want the null(s) deep (and steerable)
to kill the strong, unwanted station.

This characteristic demands the SAME considerations as required for a
sharp beam of high directionality.


Actually, no.
You can form a deep null with a much simpler antenna system than for
high directionality.

Simpler does not invalidate SAME consideration.

All you need is to "cancel" the signal from the undesired direction.

If you had two verticals spaced some distance apart, fed by equal length
transmission lines, and one is polarity reversed, you get a fairly sharp
null on the line perpendicular to the line between the antennas.
(e.g. a signal coming from broadside will exactly cancel in the combining)

Hence my referenced Cardiod antenna available for modeling with EZNEC.

A loopstick antenna on a ferrite core or a multiturn loop, as popular in
direction finding, is another example with a fairly sharp null.

Mike has explicitly rejected loop solutions.

Now.. if you want one null, and one null only, that gets a bit trickier
in a small space. I don't know that you can do it with only two
elements (haven't thought about it much).

And if you want to steer the null.

One traditional approach in direction finding is to use a goniometer or
an adcock array.

Something I've already offered (Bellini Tosi Antenna, as well as
Wullenweber) - and has been rejected/ignored. Repetition doesn't seem
to stand much chance against the ongoing cult examination in trying to
parse the entrance qualifications for the Dallas Files.


If we were to select the antenna that matches your quoted specs above,
it would be called the Cardiod (example available in EZNEC). Problem
there is the 30dB null isn't steerable (not enough elements). And it
is large (too large for the back yard):
1. Too tall for most to build.
2. Elements too far apart (out of necessity for, dare I say it?
Phasing).

that's the "one null and one null only" problem.

Which loops (as in recurse, not a pun) us back to the top.

73's
Richard Clark, KB7QHC

On 7/19/2011 8:08 PM, Richard Clark wrote:

If you had two verticals spaced some distance apart, fed by equal length
transmission lines, and one is polarity reversed, you get a fairly sharp
null on the line perpendicular to the line between the antennas.
(e.g. a signal coming from broadside will exactly cancel in the combining)

Hence my referenced Cardiod antenna available for modeling with EZNEC.

Cardioid has only a single null and is a "end fire" configuration. I
don't think (esp with short spacing) you can get as deep or narrow a
null as with a W8JK style antenna(short spacing, out of phase).

two 180 degree out of phase antennas can be very narrow, even with small
physical extent.



A loopstick antenna on a ferrite core or a multiturn loop, as popular in
direction finding, is another example with a fairly sharp null.

Mike has explicitly rejected loop solutions.

Perhaps big loops were rejected.. what about physically small loops.


Now.. if you want one null, and one null only, that gets a bit trickier
in a small space. I don't know that you can do it with only two
elements (haven't thought about it much).

And if you want to steer the null.

On 7/20/2011 8:01 PM, Jim Lux wrote:
On 7/19/2011 8:08 PM, Richard Clark wrote:


After reading too many postings from this thread I wonder why anyone,
excepting myself just for this once, bothers to comment.

Who bleeping cares about this thread? This is not a great debate even
if you consider any of the the best ones here "great debates".

Which they mostly aren't.

tom
K0TAR