Hi Jose,
I think that we are going to agree to disagree as to how these type of
cardioid antennas work. Yes you are correct that there is a vertical antenna
mode, but you can't ignore that the induce current from the H field has to
be managed. Lets say that the induced currents from the E and H fields
differ by 90 degrees or put it another way the currents are -45 and +45
degrees. These cannot be added to generate a cardioid. However, as these
currents flow though the termination resistor, then the phase difference
diminishes because the resistor tends to be the dominant reactance in the
antenna. At a certain resistor value the induce currents can be equalise so
that they can be added in a similar manner like a sense antenna in a loop DF
system. As the relationship of the E and H field is constant over a wide
bandwidth and so is cardioid.
If you phase 2 verticals you will find that the rear pattern does shows a
good high angle FB. This is not the case with a Flag. Now phase a loop with
a vertical and you will see the opposite is true. Just like a simple Flag.
73
Andrew
Hi Andrew
He concept is very simple, you can phase 2 verticals. 3 verticals or 4
vertical. See you got, two verticals in phase give you a cardioid pattern,
only one deep null on the back. Moving to 3 or 4 verticals gives you two
deep side nulls plus some front back.
The SAL does not have side lobe nulls. The feed system does no change the
fact that you have only two vertical wires as antenna, the inclined wire can
be describe as two vectors one vertical and another horizontal. The two
vertical vector and the center of the inclined wire define the pattern.
See the case of a DHDL, invented by George AA7JV, the vertical wires are far
apart and the two inclined wires vertical vectors are half way each other.
The DHDL has 4 verticals as the Waller Flag with two independent loops
making 4 verticals as well, but the gain of the DHDL is 1-2 db below the
WF. Why? the reflection between the two loops and the proximity of the two
vertical vectors impact the DHDL pattern, as well the two verticals wires
on the SAL.
The SAL and the DHDL does not have side lobe nulls.
One Loaded loop or EWE, K9AY RDF is close to 9 db, the SAL and DHDL are
slighted better RDF 10 db on EZENEC, but again on practice, measuring the
diagram of irradiation the SAL never achieved the extra 1 db in RDF. Two
loaded loops has side lobe nulls and RDF is close to 12 db, very similar to
3 element yagi azimuth diagram. Both antennas, the SAL and the K9AY have
impressive deep null on the back, giving you a good front back. It is a null
on the back , very different than front rear, that take the 180 degree
energy between the front and the back.
You can find several stations using two DHDL in phase and it does work, but
you wont find any array of two SAL because the phase is so critical that
became impractical.
73's
JC
N4IS
73
Andrew Ikin
G8LUG
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