When Art used a combination loop dipole as a three element form of Yagi it
was really an error as he has lapsed back into wavelength style thinking
where as the loop/dipole were coupled elements that formed a collinear array
which obviosly could not be used succefully in this arrangement. Art then
changed the beam aproach by removing the capacitance from the element loops
and then coupled the loops in series form with the dipoles attached
which did not require a specified spacing between the elements which then
formed a nice beam via close coupling. The beam was fed via a delta feed but
Art wanted a broader frequency range. He did this by feeding the coupled
array with a separate dipole with a delta feed and placed this close to and
parallel to the leading dipole /loop which formed a capacitive coupling to
the antenna array. What happened here is that energy was fed to the delta
feed dipole and then the energy travelled along the dipole and then
transfered to the antenna array at the point of best match. This broadened
the frequency span of the array in a similar way to varying the connection
point of a delta fed antenna such that the operating frequency even when
changed was at the array resonant point. So upto now Art had made a
loop/yagi dipole with a ladder type loop that could be used in excess of one
octave as well as making a coupled array with a moveable resonance but with
the declining sunspot cycle comming decided to work on a 160 meter dipole.
He made the element as long as possible and then added the loop with a
variable capacitor, he also fed the dipole/loop antenna with a capacitive
coupled delta fed dipole that also contained a variable capacitor and then
realised that if he added a variable inductance to the loop dipole he would
in reality be duplicating the 'T' circuit that was used as a inbuilt tuner
in a solid state tranciever where he could disconnect the 'T' circuit in the
radio and use the controls to control both vaiable capacitors such that the
input impedance would always be resistive regardless of the spacing of the
former capacitive coupling which was now an inductive coupling. Immediately
it was seen that if the capacitances were made as small as possible (2 pF or
less)and left fixed, together with an ideal spacing between the feed and the
combo dipole the band pass of the antenna was around 5 to 7 Khz and could be
moved anywhere on the band by just varying the inductance. Varying the
inductance was done quite easily by the addition of a variometer to the main
inductance. The antenna worked extremely well at around 50 watts in the
horizontal position together with a few db down on the sides. Since Arts
tower was a fold over he was also able to operate the antenna in the
vertical position with a low operating angle because the antenna being
collinear in form was less dependent on ground conditions or the need for
ground radials.
Attacks can now begin ,.......the next report will detail what the computor
says about its characteristics on 160M and what an overlay on a beverage
pattern shows which will surprise many plus details how the antenna can be
reformed to provide a cluster of radiators and confirm again that one could
have a antenna array
that is not controlled by wavelength, with a high Q bandpass that not only
was moveable but always operated at a resonant point and where the delta
feed was devoid of radiation i.e. lossless feed and match.
Still going......
Art Unin KB9MZ.........XG























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