A W9RE designed 8-circle PCB is used for phase control at the center of the array. This design utilizes Magic-Tees to combine in phase elements, of which one pair is routed through a 180 degree transformer and delay cable. The delay cable is currently cut for 65 degrees at 475 kHz (approx 318 ft), resulting in a phase shift of 115 degress between front and back elements.
The feedlines from each element to the central phasing box are all approximately 700-710 ft long. After the first cable was installed, an analyzer was used to determine the quarter (1/4) wave frequency (X=0 with open end). That frequency was measured to be 291 kHz. All subsequent cables were cut to that electrical length to ensure a consistent phase relationship between all elements.
Direction switching is accomplished via an NO3M designed control card. This device is remotely located about 600 ft from the shack and receives switching commands from a desktop controller via an RS-485 serial buss. Three (3) outputs from the control card are then routed to the central phasing box of the 8-circle array, which is another 600 ft away. The three (3) outputs allow selection of any eight (8) directions.
Information to be added.
Initial tests indicate a F/B of at least 22-28 dB, but is very dependent upon whether a station off the back is in one of the deeper nulls.
Below is an ARGO screen capture taken when switching between the Southwest (SW) and Northeast (NE) directions.
The signals from top to bottom are: WD2XSH/7 CW beacon in LA, WG2XKA (WSPR2) in VT, WG2XIQ in TX (WSPR2) and WG2XXM in OK (JT-9). It is clear to see when the direction is switched. Note the dog-boning of WD2XSH/7’s CW, which has a very faint trace when switched NE.
Further data was collected using WG2XKA’s WSPR2 signal, 2014/03/03, switching between East (E) and West (W):
2336 -20 -0.1 0.475726 0 WG2XKA FN33 30
2342 9 -0.3 0.475726 0 WG2XKA FN33 30
2346 -20 -0.0 0.475726 0 WG2XKA FN33 30
2350 6 -0.0 0.475725 0 WG2XKA FN33 30
2356 -19 -0.0 0.475725 0 WG2XKA FN33 30
0000 5 -0.2 0.475725 0 WG2XKA FN33 30
0006 -18 -0.2 0.475725 1 WG2XKA FN33 30
0014 9 -0.3 0.475724 1 WG2XKA FN33 30
0022 -16 -0.1 0.475724 1 WG2XKA FN33 30
The above data shows a F/B range of 23 – 29 dB.
- RG6 Coax (Commscope F660BVV); phasing lines + delay cable: 5912 ft (1802m)
- 1 in. alum. tubing; elements: 192 ft (58.5m)
- #17 Fence wire; radials + top-hat wires: 7200 ft (2195m)
Future improvements and Modifications
Replace passive elements with hi-impedance elements using hi-impedance amplifiers to improve operating bandwidth, reducing potential phase errors over arbitrary length feedlines. Array will still be primarily an MF system due to broadside spacing.
More accurate element placement with hi-impedance elements to reduce spatial phase errors (top-loaded elements require some re-location due to inhibiting vegetation)
Attentuator pad on the non-delayed elements to equalize amplitude of front:back elements, maximizing null depth potential. Attentuation has not been measured through the 65 degree phasing cable at 475 kHz (cable length approx. 375 ft, RG6), so this is perhaps a moot endeavor
Implement an 8-circle variation using 0,-106,106 degree phasing where all elements are “active” simultaneously, smaller diameter circle (800 ft), better RDF (13.4))
The last two elements have been installed and connected into the system. Array construction is complete.
Two (2) additional elements were added today. The array is now switchable NE, E, SW, W.
Direction control has been added. Array can now be switched Northeast and Southwest
Four (4) elements have been installed and connected to the central phasing controller. There is currently no direction switching, so array is fixed Southwest.
Testing various mechanical variations of vertical elements, including all wire, various top wire lengths, tubing elements, passive element components, active element amplifiers, et.al.