JUMA TRX2 DDS Guide

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

Selecting Service Mode (do the calibrations)
When powering on JUMA-TRX2 keep PWR button pressed until you see the
text Service Mode on the LCD display. Release button. Now you are in the
Service Mode.
With DISPLAY button you can walk through calibration menus
With FAST button you can save your calibration values and switch to the
normal operating mode
If you want to leave Service Mode without saving do the normal Power Off
with PWR button
Set reference oscillator frequency
When doing this calibration JUMA-TRX2 should be in its normal operating
temperature.
Method 1.
Measure 30MHz-reference oscillator output with precision frequency counter.
Multiply result with six (AD9851 internal clock frequency) and dial this value in
with VFO knob. For example: If you measure 29.999.850Hz multiply this with
6 = 179.999.100Hz and dial this value in. Default value is 180.000.000Hz
Method 2.
Listen to a exactly known carrier frequency. Change between LSB and USB.
Adjust JUMA-TRX2 VFO so that LSB and USB sounds are at the same pitch.
Read JUMA-TRX2 frequency display, compare it with known frequency and
calculate correction factor for JUMA-TRX2 DDS clock frequency.
Power supply voltage meter
Measure JUMA-TRX2 supply voltage with accurate DVM. With VFO knob
adjust the voltage reading on the LCD display as close to the DVM reading as
possible. Calibration value is also shown on the LCD display. Default Cal
multiplier (scaling value) is 132.
Indicator tones (Beep) length
You can adjust JUMA-TRX2 user interface indicator tone length. Long beep is
always ten times longer than short. If you dial in 0 (zero) no tones are played.
Maximum value is 100ms. Default value is 50ms.
S-meter scaling
S-meter adjustment is an iterative process where main board AGC threshold
trimmer R53 and S-meter scaling values are adjusted to get correct and
accurate S-meter reading. Please see main board adjustment procedure for
details. If necessary you can check DDS S-meter board operation by applying
1VDC voltage to J3-pin8. S-meter should read S9 with this voltage.
When this adjustment is done correctly your JUMA-TRX2 S-meter shows true
S-units and decibels.

FWD Power meter scaling
With this adjustment you can fine tune JUMA-TRX2 output power display to
show actual RF power output. Connect accurate wattmeter and dummy load
to your JUMA-TRX2. Select first TUNE mode and then PWR meter display.
Push PTT and read JUMA-TRX2 display and the external Wattmeter.
Example:
External meter reads 9W and JUMA meter 8W and calibration value is 23.
Divide 9/8 = 1,125 and correct calibration value with this. New calibration
value 23 * 1,125 = 25,875. Go back in the Service Mode and dial in new
calibration value 26. Save this and recheck the readings.
Drain current (ID) meter scaling
This adjustment is not necessary but if you like to check and calibrate your
JUMA-TRX2 PA ID current display do following:
First select TUNE mode and then ID current display. Push PTT, read JUMA-
TRX2 ID current display and measure voltage across R17 or R21 in the PA
board. Calculate drain current from the voltage = U / R. If you measured
0,209v divide it with R17andR21 value. 0,209V / 0,11R = 1,9A. If necessary
correct ID scaling Cal mult value. Procedure is same as in power meter
scaling.
See also PA board tuning instructions. Particularly bias current adjustments.
Return to the ”factory default” values
In case you want to return to the ”factory default” values select on the LCD
display:
Push FAST long =
Factory defaults
And press FAST button about five seconds.