Hi Roger,
On cursory review, here are some thoughts that come to mind...
>> I sum the two middle elements with a two way hybrid combiner, and the
middle, front and rear elements with a three way hybrid combiner
(1) How are you achieving the plus and minus 90 deg phase shifts for the
forward and rear elements respectively with respect to the mid elements? I
see the inverter un-un but is the three way combining all of the inputs
in-phase? A hybrid quadrature (bridge) coupler would normally be used to
generate the necessary 90 degree phase relationship, or which the front or
rear would be offset by 180 deg. Your circuit diagram does not elaborate on
the coupler, but it does not look like a hybrid quadrature because there is
no "dump" port.
(2) You mention phase delay line but I did not see that in the on-line
schematic. If you are using phase delay line feed method, bear in mind that
there will be mutual interactions between the driven elements. These will
need to be evaluated (through testing) and included in the delay line
calculations. W7EL has a good program out there to do this.
(3) If using hybrid quadrature, I seem to recall that the mid antenna "port"
of the bridge operates at half the impedance of the "front" / "rear" ports
(would need to look through my notes to verify). I seem to recall that when
the two mid antennas are connected in parallel, the resulting combined
impedance (half of one antenna) then matches the port. If you are using a
combiner, the input impedance may be the same as each output and there could
be an impedance mismatch between the 2-way combiner and the quadrature
bridge.
Hope this info helps you & good luck on your project.
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Roger
Parsons via TowerTalk
Sent: Wednesday, October 01, 2014 10:49 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Receive 4-Square
I would appreciate some help with my 160m receive 4-square antenna. It has
horrible directivity which I presume means that I have the phasing or
amplitudes wrong.
The array consists of 4 passive vertical antennas, spaced quarter wave
across the sides, each 25' high and top-loaded. Each has 8 50' ground
radials, is resonant on 1850 kHz and is loaded to 75 Ohms - all exactly as
W8JI. I am confident that this part of the array works properly.
There is a pdf copy of the schematic at:
https://www.dropbox.com/s/2wg3kj9r42woqbi/Vertical%20Array.pdf?dl=0
Ignore the excessively complex control circuitry - that bit also works fine!
I sum the two middle elements with a two way hybrid combiner, and the
middle, front and rear elements with a three way hybrid combiner. These are
commercial units and are claimed to have excellent phase and amplitude
balance. The only real difference (I think) between my circuitry and other
published designs is that the two way combiner allows me to use a single 75
Ohm phasing cable rather than two in parallel.
So what have I done wrong?
73 Roger
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