Download 5. Executive Summary The Automated Antenna Controller (AAC) is

5. Executive Summary
The Automated Antenna Controller (AAC) is an improved control unit designed to automatically tune the
MFJ-1786 and MFJ-1788 loop antennas. The AAC effectively tunes the antenna; matching the antenna
and radio impedances for lowest SWR allowing operators more time for transmitting. The AAC also
displays SWR, frequency, and forward and reflected power more accurately than the existing antenna
controller.
Figure 1: Product Graphics
The following constraints will ensure that these demands are satisfied. The AAC must be capable of
measuring and displaying up to 150 W RF power from an HF amateur radio with an accuracy of ± 1W. It
should also measure and display frequencies ranging between 7 MHz to 30 MHz with a resolution of ± 30
kHz. Current draw needs to be less than the rating of the supplying power supply, the MFJ-1312D AC
adapter, limiting the current consumption to a maximum of 300 mA. When tuning, the device will have to
send a pulse to the antenna of varying modulation lengths while providing 12 VDC for the duration of
each pulse. A maximum of 3:1 SWR must be achieved. The AAC must have an SO-239 connector to
interact with the operator’s radio and antenna. The AAC must use components that are already present at
the MFJ manufacturing facilities whenever possible. It should also meet MFJ’s 12-months limited
warranty. The dimensions should not exceed 4in x 7in x 7in. For safety reasons, the controller must alert
operators when the SWR is at unsafe levels and must be isolated inside a box to protect the user and
equipment from burns of both temperature and RF nature and electric shock.
To comply with these constraints, these design options were selected. The PIC18F2520 microcontroller
was chosen for its features and capabilities over other microcontroller offered by our customer, MFJ, Inc.
The ADC is used to calculate the forward and reflected power from the representative voltages received
from the directional coupler small signal output. After a full wave rectifier along with D-flip flops
convert the input waveform into a readable form, the capture module is used to calculate the operating
frequency of the radio transceiver. The pulse width modulation (PWM) module is used along with an Hbridge to control the motor that tunes the antenna. After all these values are calculated, they are displayed
on the LCD. Finally, to comply with the antenna motor requirements, the voltage supplied to the motor
was constrained to 12 VDC ± 1V. The microprocessor is supplied with the standard 5 VDC with a 300
mV tolerance, which allows for a 20mV cushion for the microprocessor’s requirements.
The AAC is more readable, more accurate, and much faster than the previous antenna controller used with
the MFJ-1786 and MFJ-1788 loop antennas. Its multiple displays and automation also make it much
easier to use. With its increased accuracy and ease of use, the AAC will be a must have device for avid
hams and beginners alike.