Automatic tuning

I obtained a Yaesu FT1000MP which has a Computer assisted Transceiver connector. This basically is a serial port from which you can control the transmitter. Popular software packages like Ham Radio de luxe and MixW use this interface. When scanning the bands the nice High Q of the magnetic loop antenna becomes a disadvantage: You keep on tuning the antenna.

So the following project is on it's way.

  • Yaesu FT1000MP connected to a PC with 2 RS232 ports
  • Ham Radio Deluxe (http://hrd.ham-radio.ch) version 3.3Beta Built 1072 or later. (Earlier versions do not allow you to set the speed of the 3rd party com port, tnx Simon) One com port controls the Yaesu, The 3rd party serial port option is enabled and talks Kenwood Language. I believe MixW has similar features but I did not check those, yet.
  • An Atmel Mega32 prototype pcb. The RS232 of the Mega32 talks to the PC in Kenwood language. The rest of the I/O pin's control a 16*2 LCD and the motor in the Mag loop. A 4*4 keyboard for entering parameters is present but not used yet.

The goal is that when tuning the transceiver from the knob or the program on the PC the antenna tuning will follow automatically. SWR under 2:1 should occur when deciding to transmit.

The BASCOM AVR software asks the PC at fixed intervals where the transceiver is tuned to. The answer is processed and used as an entry in a lookup table with potmeter feedback values. The difference between the EERAM stored potmeter setting and the current setting is used to steer the tuning motor using Pulse Width Modulation.  The lookup table currently has (fake) entries at 10 kHz intervals. User interface is in the form of a 16*2 LCD

At this moment the software is in Beta stage and a hardware simulation is running using the above setup and a potmeter for feedback. What remains is adding some electronics (H-Bridge) to convert the I/O pins for left, right, on/off and Pulse width modulation to something the motor will work on.

The next hurdle will be to keep the RF away from the controller, especially the feedback pot-meter. 

Some preliminary calculations have shown that the potmeter on the main shaft of the butterfly Capacitor together with the 10 bit A/D converter will not be accurate enough. In that case I will replace it with a shaft encoder and some switches. More wires and signals then the pot but they are digital and easier to tame then an Analog voltage coming back from the antenna over a cable in parallel to the feeder.