[Hi-zreceivingarraydiscussions] Homebrew 4-square based on Hi-Z amps

[Bob Zavrel]

I just finished building a homebrew 4-square. The elements are 21 foot sections of 1 ½ galvanized pipe. I mounted 12 foot pressure treated 4x4s in the ground with cement. A metal pipe stand-off is used about 9 feet off the ground...the end is threaded, so a PVC threaded "T" is screwed on the metal pipe stand-off...then the 21 foot element is inserted through the T. The threading connection acts like a hinge. The bases use plastic funnels (like for oil drainage) upside down on small boards...that's all there is to the mounts. Plastic drain pipe keeps the amps dry, and extra coax lengths are wound around maritime-type rope fasteners...to keep the coax from running rampant, and looking ship-shape.

The homebrew controller can select 8 directions on both 80 and 160 meters. I can check the integrity of the four feedlines and the pre-maps from the shack by simply monitoring the current consumption to each element. I use 1 ohm resistors in series with the supply lines to each amp and then shunt with a 100 ohm resistor in series with an old 0-1 mA meter... a rotary switch selects the element to be measured. The current consumption is remarkably consistent among the four amps (about 30 mA each). I use identical feedlines to each elements (240 feet each), and use passive L/C phase shifters rather than transmission line phasors. This allows me to fine adjust the phasing in the comfort of the shack. Without adjustment, I achieved >25 dB F/B ratio..fine tuning for slight environmental variations (temp, moisture, etc) can null better than 30 dB F/B. Amplitude balance of the amps/lines is excellent. The amps are everything I hoped for...the weakest links in the array's performance are environmental and phasing accuracy..not the amps. I also use the Hi-Z 75/50 ohm transformer to convert the entire system's 75 ohm standard to 50 ohms just before the RX input. I use the Curtain-Zepp (last April QST) for TX. Since the directive pattern is tighter on the 4-square, the S/N ratio is about 3-4 dB better on the 4-square. I use a simple 1.843 MHz clock oscillator run on 3 AA batteries mounted in an electrical box. A 10 foot wire acts as an antenna. I place it about 200 feet from the array and can measure F/B ratios very accurately by turning off the RX AGC, and measure the difference in audio voltages...the dB differences will give you a very accurate mapping of the pattern. The unit is still generating a very low-power signal 2 weeks after turning it on...just enough to give me a reading.

The controller  is a very flexible operating unit, but also was designed as an experimental platform.

See you on the bands!

Bob, W7SX