Ve6fi Amateur Radio
80 meter 4 square
& 80 meter rotatable and tuneable dipole
Above - installing vertical for the 4 square
Above - 4 square 80 meter controller. Cable are 50 ohm 1/2 foam at 1/4 wavelength electrical to the base of the verticals. Cables are all the same length. The controller did not come with any schematic and did not specify where a person installs the inductor and capacitor to adjust the phases to other than -90 and -180 degrees!
Above is the pickup for the power dumped into the dummy load. Remote pick up is connected to the SWR meter in the shack. The 4 square controller is also in the shack. It indicates 4 directions as well as one mono position where it just connects to one vertical.
Above is the box at the base of the verticals. It includes the coil to ground to discharge static electricity and for some lightening protection.
The 1/4 wave radials are soldered to the copper strip surrounding the vertical base. The radials are soldered to the copper strip and a ground rod is also inserted at the base of each tower.
80 Meter Rotatable Dipole
The amateur radio station VE6FI is building a rotating (directional) 80 meter half-wavelength dipole
antenna that will be mounted horizontally 80 feet in the air. I was encouraged to build this antenna
by my readings in Tom Schiller, N6BT book 'Array of Light' I have the physical antenna designed but it
is not built yet. The controller described below is an integral part of the system and it was designed
and built by Ian Burn ve6ob with his son in law Colin Ve6YD doing the mechanical work on his new
The antenna will be built of aluminum pipe and tubing and will be about 100 feet long. In order to tune
it from 3500 kHz to 4000 kHz (the full range of the 80 meter amateur radio band) two adjustable loading
coils will be mounted at the centre (photos of coils are attached) . An electric motor operating at 12 VDC
will expand and compress the coils changing their inductance and the resonant frequency of the antenna.
In order to keep track of the current coil position and hence the frequency of the antenna, a magnet on
the motor shaft closes a reed-switch once per revolution. Thirty five revolutions move the coil from fully
compressed (3500 kHz) to fully expanded (4000 kHz). By counting the number of electrical pulses produced
by the reed-switch it is possible to determine how much the coil has changed. At the coil's fully expanded
position an upper limit switch is activated.
The control system for tuning the antenna has two inputs from the top of the 80 foot tower:
1. One pulse (reed-switch closure) per revolution of the motor output shaft
2. A switch closure when the coil is expanded to it limiting position (4000 kHz)
The control system outputs are:
1. The 12 volts to operate the motor. The polarity is reversed to change motor direction. An UP-DOWN switch
operates the motor.
2. A Liquid Crystal Display (LCD) that shows the calculated current frequency of the antenna as well as
notification of having reached the upper or lower limits of travel.
Re-calibration instruction are provided if the limits are exceeded. A lock-out relay, connected to the limit
switch disconnects the power to the motor to prevent the coil from over-expansion. A similar relay operated
by the microcontroller disconnects power to the motor if the lower calculated frequency goes below 3500 kHz.
Any time the limits are reached, the system needs to be re-calibrated by moving the coil to the fully expanded
position until the upper limit switch closes. Light emitting diodes (LEDs) indicate when the motor voltage is
increasing or decreasing the frequency as well as LEDs indicating if the upper or lower limits have been reached.
The coil position is retained in the microcontroller's non-volatile memory so that the next time the unit is
powered up, it remembers the last position of the coils and can continue from there without re-calibrating.
The control circuit is attached along with the following photos:
The picture below shows one of the variable inductances. The plastic screw rod shown at the rear will allow the coil
to expand and contract. The inductance varies from 5 to 10 microhenries. The threaded rod is turned by a 12v DC motor
The picture below shows both coils. These coils are located at the center of the 80 meter dipole. They allow the dipole
to be tuned from 3500 Mhz to 4000 Mhz. The complete assembly is housed in a four inch PVC pipe for weatherproofing.
The picture below shows the schematic of the controller. The code would be available from Ian ve6ob Notice the two Programmable
chips 16F684. Notice the UP and DOWN limit relays as well as the Direction Relay. Opto isolators are utilized to isolate circuits.
There is only one control on the front panel.
Below is the circuit board for the controller built at home and shown with the traces tinned. The layout was done with
Proteus software but the etching was done at home says Ian.
The picture below shows the stuffed circuit board for the controller. The circuit board for the display is on a separate board.
The picture below shows the box containing all the circuit boards and the external controls. There is only one switch
to operate and that will allow the resonant frequency of the dipole to be raised or lowered. This will allow the resonate
point of the antenna to be tuned anywhere in the 80m band. This will allow the SWR to be minimum at the operating frequency.
The frequency is displayed on the LCD screen. Neat!
The picture below shows the display on the LCD screen. When this message appears one has to just tune the frequency
down to 3.5 Mhz and that will trigger the reset. Then all the frequencies would be calibrated.
The picture below indicates what the antenna is tuned to at this time.
The picture below shows the display which would come on the screen once the power comes up. The controller
stores the last frequency that the antenna was tuned too. So if you return to the station after being away for
a week and turn on the power, the controller remembers where the antenna was tuned too. No calibration is required. Neat!
Modelling the physical Antenna
EZNEC ver. 5.0
80m dipole 16/03/2018 3:05:19 PM
--------------- WIRES ---------------
No. End 1 Coord. (ft) End 2 Coord. (ft) Dia (in) Segs Insulation Conn. X Y Z Conn. X Y Z Diel C Thk(in) 1 0, -46.5, 90 W2E1 0, -1, 90 1 33 1 0 2 W1E2 0, -1, 90 W3E1 0, -0.5, 90 1 1 1 0 3 W2E2 0, -0.5, 90 W4E1 0, 0.5, 90 1 1 1 0 4 W3E2 0, 0.5, 90 W5E1 0, 1, 90 1 1 1 0 5 W4E2 0, 1, 90 0, 46.5, 90 1 33 1 0
So these are the dimensions one can use for modelling in Eznec. The element diameters where modeled with
1 inch diameter. Then after you have to do the taper schedule to fit the actual dimensions of pipe/tubing that
you are using. If you require the rest of the data or more information contact Denis at email@example.com