DDS Unit Construction Guide of TJ6A pro
The main board, PA and the DDS function of TJ6A pro is the same with TJ6A. The different
part is the DDS unit in which the S meter unit (SM unit) is add (see picture below).
The DDS output filter circuitry is modified in the “pro” version to
remove “birdies” caused by DDS unit.
Besides, the phone connector is added on the front panel. This guide
only discusses the construction of the “pro” DDS unit and calibration of
the S meter.
Assembling and Wiring
The assembling of the LED SM is illustrated in the following pictures.
1. Insert the FFC cable, with blue plastic part up.
2. Position the LED unit and fasten with 2 screws. Be sure to tighten the 2 screws.
3. Bend the FFC cable, so that it does not block the connecting pads of the decoder.
Mount the decoder on the front panel. Extend the decoder leads and solder them to the PCB
pads respectively.
4. When the whole DDS assembly has been finished, it is suggested to apply a drop of silicon
glue between the LED PCB edge and the front face to prevent incidental short circuit. The
clearance between the LED and the front face is wide enough, but if the 2 screws become loose,
the LED’s metallic part might contact the front which is connected to GND, damaging the LED’s
and the FFC cable.
The wiring of the Pro DDS board to the main board is illustrated as the following picture.
After the AF GAIN
control, and PH, KEY,
and MIC connectors
are mounted on the
front panel, wire them
as shown.
Connect
speaker’s “+” lead to
output lead of the PH
connector (red line);
connect speaker’s “-”
pin to the GND lead
of the PH connector
(yellow line).
The speaker is
disconnected when
the earphone is
plugged in.
From the wiring
you can see that
“PHONE” of MIC
connector is directly
connected to audio
output of CN3.
“PHONE” signal is
not disconnected
when the earphone is
plugged in. “PHONE”
of the MIC connector can be used as DATA OUT for PSK31 service.
Connect AF G IN
control to CN2 of the main
board as shown above.
The S meter
signa
l from CN2. Connect
CN5 of DDS Board to the
signal arm of AF GAIN
control (see above picture).
A
picks up
If the black plastic PH connector is supplied in the kit, please connect as shown below.
Solder all the connections.
The connection of the MIC connector is illustrated below.
The definition of the MIC connecting pads on PCB is shown below (Viewed from front of
radio). Unlabeled pads have no connections. Extend the connector leads to the PCB pads
respectively.
After the M
and
adjacent “GND” pad to CN5 of the main board. Connect “PHONE” pad to PH connector as
IC connector leads are connected to the respective PCB pads, connect “MIC” pad
shown in the previous picture. “MIC” of the MIC connector can also be used as DATA IN for
PSK31 service.
a f SG-2020 so as to suit the
t oHowever, you may wish to define the connector wiring as th
NUE
-PSK Digital Modem connector. Then wire the 8-pin connector leads to the PCB pads
according to the connector wiring as shown below.
The connection of the KEY connector is illustrated as the fo ng picture. Solder the
indic
ated lead (the tip lead) to the KEY pad on PCB. Since the front face is GND, it is not
necessary to solder the GND lead of the KEY connector to the PCB.
llowi
Phone Connector
PH connector is the mono phone connector. When the earphone is connected, the louder
speaker is disconnected.
IF SET Button
The “IF SET” feature has been discussed in the Instruction Guide of TJ6A. TJ6A pro has a
button to access IF SET mode. Press IF SET button of the DDS unit, the DDS unit enters IF set up
mode. Press MEM to exit this mode.
Calibration of S meter
The S meter circuit is used with LM3915 which drives 10 LEDs, providing a logarithmic
3dB/step analog display. Each 2 LEDS stands for an S. For example, LEDs 1 – 2 stands for S6
(6.3uV), LEDs 3 – 4 for S7 (13uV), LEDs 5 – 6 for S8 (25uV), LEDs 7 – 9 (50uV), LEDs 9
8 for S
– 10 for 59+.
TJ6A pro uses the dot display mode to save power. The S meter displays the signal peak. For
bar display mode, connect
etween 10 – 100ohms.
b
After check
calib
rate the S meter. Trim VR2 of the DDS board (VR2 is beside U16) until all the LED’s are lit.
ing, apply power. Try to find a strong signal (S9+) of either SSB or CW to
Pin 3 to Pin 9 of U16 (LM3925) with a hookup wire or a resistor
If you have a standard signal generator, input a 50uV signal into ANT of TJ6A pro. Trim VR2
until the 8
th
LED is lit, which stands f
or S9.
Louder Speaker Liner
To prevent the friction occurs between the speaker cone and the casing, it is suggested to
insert a hard paper liner (around 1 mm thick) between the speaker frame and the casing. The
speaker cone friction causes hoarse or distorted sound when the strong signal presents.
Alternatively, 4
the l
iner offers better sound. Draw the shape of the speaker on a piece of hard paper (or other
materials), and then cut a opening the size of the speaker cone. Position the liner on the speaker
mounting, and then put th
uc
m h force to tighten the screws. Too much force might distort the speaker metal frame, resulting
in permanent damage to the speaker (unclear and distorted sound). The liner can be made larger,
because the paper liner breaks easily if the flange is too narrow.
spacers can be used to raise the speaker frame a little from the casing. However,
e speaker on the liner. Insert the screws and tighten them. Do not use too
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