JUMA-TRX2 DDS / Control Board adjustments
OH2NLT 22.08.2007
Before you get on the air no DDS board adjustments are really necessary. I/Q
balance adjustment is however recommended. Software calibrations or
adjustments are for fine tuning your JUMA-TRX2 meters and displays.
I/Q balance trimmer
With trimmer R42 in the DDS board I/Q balance can be fine adjusted. I/Q
balance has direct influence to the unwanted sideband rejection. Theoretically
digital signals driving the mixer switch should be phased 90 degrees off each
other. Order of I signal and Q signal (which is leading) selects LSB or USB.
This switching is done in the main board. Practical circuits are not perfect and
require I/O balance fine-tuning to get best possible unwanted sideband
attenuation.
Adjustment is simple:
Select your favorite operating band and feed about S9 (50uV) CW signal to
the antenna connector. Switch to other sideband. Signal should disappear.
Adjust R42 to find minimum value. You may perform this check / adjustment
also with other frequencies (bands). Adjustment is not exactly the same for all
the frequencies and you may have to compromise in which suits best for your
listening needs. Find steady strong carrier from the air to do the adjustment if
you do not have a signal generator.
I/Q balance affects also TX unwanted sideband rejection. It is enough to do
this adjustment with RX but if you wish you could check TX sideband rejection
with dummy load and another receiver.
Software adjustments (calibrations)
There are several adjustments or calibrations done in the DDS board control
software. Calibration values are stored in the dsPIC30F6014A microcontroller
non-volatile memory (EEPROM). In the very first startup when the EEPROM
memory is ”empty” default values are written in to the EEPROM. These
default values are so close that you can operate JUMA-TRX2 without doing
any calibration adjustments. If you like to fine tune your JUMA-TRX2 continue
reading.
Calibration adjustments
Set reference oscillator frequency
Power supply voltage meter
Indicator tones (Beep) length
S-meter scaling
FWD Power meter scaling
Drain current (ID) meter scaling
Return to the ”factory default” values
