JUNIOR 1D
Again and again I had requests from Junior1 builders,
whether digital frequency displays or reception areas can be
extended. I advise against these interventions. The questions
motivated me, however, to develop Junior1 further. J1D is
the successor model of Junior1, specially developed for HAM
RADIO enthusiasts without HF measuring station.
The only adjustment work is to adjust the LCD
Display contrast!
J1D shows the following changes: An Atmega AT644 micropro-
cessor is used as a “brain”. This provides the control commands
for the DDS, the LCD display and the preselector. All buttons as
well as the redary encoder are also queried at the AT644. The
reception concept of Junior1 has proven itself, which is why it
was largely adopted in J1D. However, the large reception area
requires a completely new input circuit. The preselector realized
with high-quality ring cores provides a good mirror frequency
suppression. At the output of the preselector, the RF voltage is
converted by the field effect transistor in a low-impedance man-
ner and supplies this voltage to the first mixer. At the output of
the mixer, the first IF is at 10.7 MHz. If you want to upgrade the
receiver, the 10.7MHz ceramic filter can be replaced by an 8-pole
quartz filter. The board is ready to handle it.
The first IF enters the A4100D. This converts the 10.7MHz to the
2nd IF of 455kHz. The automatic
Amplification control, demodulation and LF preamplification
Also takes the A4100D.
An SSB reception comes by direct radiation in the ZF amplifier.
The superimposed oscillator is realized with a BC547 and a ce-
ramic resonator.
By this direct method, however, the control range is lower and
there is a continuous glow of the “Field LED”. In addition, dis-
tortion of the SSB reception is possible with too strong signals.
An LM380 in conjunction with a 4Ohm loudspeaker guarantees
a strong audio reproduction.
The operation of J1D is reduced to the essentials.
The tuning steps can be selected by pressing the redary encod-
er knob. The “MEMO button” allows you to store the last set
frequency and type of demodulation before switching off the
device. The pre-programmed reception frequencies are selected
by pressing the “Amateur” and “Radio” buttons.
The “Field LED” shows the relative reception field strength and
serves as a tuning aid for the preselector.
A new battery compartment is also available.
Conclusion: J1D is a powerful SW receiver with high sensitivity
and frequency stability in a attractive design. Before we begin
now with the construction, read these important points:
1. The pushbuttons must be used in the correct position. The
stage on the button is marked as a line on the board.
2. Check the correct resistance before soldering the resistors
Value.
3. The electrolytic capacitors are absolutely polarized
soldered. The positive pole is the longer wire and the
Negative pole is marked on the housing.
4. Take your time and follow instructions.
5. Make sure you do not create any short circuits because of
Soldering eyes.
If you want to mount the IC’s (except A4100D), which is not
absolutely necessary. Frames can be used. If so take special
caution to check all pins for alignment.
