The Modulator,
After perfecting my system with the 14318kc transmitters, cw. dsb and linear amplifier , push pull amplifier and wasting so much time and energy on making, learning,teaching things it is my time to be on air finally or forget the dream forever.
So making it with my time proven modules. I have previously made the single ic modulator and mixers. Now giving it a little twist making on the copper plane. I call the copper board as a magic carpet. Better than pcb. It gives me the creative edge how to shape the project.
For working on the copper board you need small hacksaw, big hacksaw, triangular file, round file, sharp knife, marker pen, steel ruler or straight bar, some crocodile clips, little vice. one sharp steel pin, de-soldering pump & good Magnifying lence,
As for 04jan2015 see the foto
I soldered the transistors. Used BC549c. Tried to use same components so that inventory can be good.
06jan2015:- soldered all the wires, jumpers, extra capacitors.
07jan2015:- At the modulator state fixed/measured the LC valued in the Test oscillator with the frequency counter.
Soldered it.
15jan2015:- finished up.
27jan2015:- Tested OK, slight careers leakage is there, but which need to be reduced...
01feb2015:-uploaded the ckt diagram.
MY write-up for the contest.
Other items & hardware...
After perfecting my system with the 14318kc transmitters, cw. dsb and linear amplifier , push pull amplifier and wasting so much time and energy on making, learning,teaching things it is my time to be on air finally or forget the dream forever.
DSB Exciter |
So making it with my time proven modules. I have previously made the single ic modulator and mixers. Now giving it a little twist making on the copper plane. I call the copper board as a magic carpet. Better than pcb. It gives me the creative edge how to shape the project.
For working on the copper board you need small hacksaw, big hacksaw, triangular file, round file, sharp knife, marker pen, steel ruler or straight bar, some crocodile clips, little vice. one sharp steel pin, de-soldering pump & good Magnifying lence,
As for 04jan2015 see the foto
I soldered the transistors. Used BC549c. Tried to use same components so that inventory can be good.
06jan2015:- soldered all the wires, jumpers, extra capacitors.
07jan2015:- At the modulator state fixed/measured the LC valued in the Test oscillator with the frequency counter.
Soldered it.
15jan2015:- finished up.
27jan2015:- Tested OK, slight careers leakage is there, but which need to be reduced...
01feb2015:-uploaded the ckt diagram.
MY write-up for the contest.
14,194kc,
20 meter DSB MODULATOR by Indrajitsinh, VU3INJ,
For 20 meter only xtals widely available is 14318kc . Sometime we also get the 14166kc but not always. But this is far from the crowd. Most of the excitement is around 14200kc fone part. So this idea was born.
The DSB modulator using the two simple cheap easily available xtals and two TA7358AP, the 9pin SIL, FM mixer IC. Its widely available it contains one RF amp, Gilbert cell mixer and oscillator. It also cheaper than NE612 . Using two ta7358ap is a little bit over kill for a single frequency dsb exciter. Only advantage is simplicity, no critical tuning. When you are using the QRP the stability of signal is utmost important. Due to use of the DDS VFO and narrow xtal filters even 100hz deviation go dutch for some operators. This will give us a good solid stable signal and our friend will know where to find us.
The DSB modulator using the two simple cheap easily available xtals and two TA7358AP, the 9pin SIL, FM mixer IC. Its widely available it contains one RF amp, Gilbert cell mixer and oscillator. It also cheaper than NE612 . Using two ta7358ap is a little bit over kill for a single frequency dsb exciter. Only advantage is simplicity, no critical tuning. When you are using the QRP the stability of signal is utmost important. Due to use of the DDS VFO and narrow xtal filters even 100hz deviation go dutch for some operators. This will give us a good solid stable signal and our friend will know where to find us.
First IC is TA7358ap which modulates
the signal. Internal coll-pitt oscillator between pin7& pin8 is
used. Xtal here is 4.194kc. not pulled much. One stage bc549c used as
MIC AF amp with 4k7 preset as crude af level control. Another af
amplifier stage used is within ic. The DSB signal is taken out from
pin6 by resistor to make it simple. So it does not effect the
mixing/modulating much. But, a tuned amplifier is used to clean the
signal, filter out harmonics & amplify. Common BC549c is used
will give enough gain here. No need of RF transistor.
After that the signal is given to a
mixer second IC TA7358AP. Here 10.000 mhz xtal is little pulled up
higher / to change the frequency few kc upwards, trimmer capacitor is
used. But a small panel mount 50pf will be good. You can try also
the varactor diode. Single stage tuned amplifier using BC549c follows
the mixer ic to select the sum product i.e 14.194kc. Our goal is to
arrive near 14200kc.
Afterward this signal is filtered and
given to the linear amplifier. Whole strip is driven from the 5volt
regulator. Current consumption is about 45ma.... Signal is clean.
There is not much tuning or testing. Except setting 4k7 trimmer for
good sounding audio in receiver. Use whatever mic you have and
accordingly modify the mic bias resistor. All the tanks are
pre-tuned. i.e means the LC components were used as a tank in the
collpitt ocillator. By adding standard capacitors values to arrive
empirically at the given freq. The freq was measured by the counter.
Now, this same components were soldered on the board. This is
emperical and quick method of putting the fixed frequency coil for
BPF work. To simplify 2.2 micro henry ready made rfc used as first
tank. For second tank I could not find suitable candidate in
commercially made RFC. Its 22swg wire,1/8 inch dia ( a metal dril bit
used as a former) to wind it. 12 turns, tight wound. Then with the
adhesive it was made rock solid.
I had made two prototypes. First one a
year ago on vero-board and another this time on copper board. This
second prototype was mechanically more challenging than the
veroboard. I had to cut groves on the copper plane , solder the
copper pad with adhesive on copper board. But happy in the end that
it worked. To solder/brew it took me three days But, testing required
little more time as my receiver was not working....
Components details, values and ckt
diagrams follows. Please also see the PY2OHH & various TA7358
design on the web.
(x)indrajitsinh, vu3inj. Copy right.
If you find this ckt useful please enjoy and pass it on with your refinement
and above all enjoy the brewing.
Block diagram
Two prototypes:-
Bill of Material:-
Resistor | Value | Note | Capacitors | Value | Note |
---|---|---|---|---|---|
R1 | 1M | C1 | 0.1 | ||
R2,R5,R8 | 100 | C2 | 1000pf | ||
R3,R6 | 470 | C3,C6,C14,C21,C22, C23, C24,C25 | 0.1 | ||
R4,R7 | 47K | C4 | 100MFD | ||
R9 | 10K ---100K | Choose as per MIC | C5 | 10 MFD | |
R10 | 100 | C7 | 0.1 / 10 MFD | ||
R11 | 10K | C8 | NIL | ||
C9,C10,C16,C17 | 100 PF | ||||
C11,C13 | 47PF | ||||
C12,C19 | * TEXT | ||||
C15 | 33PF | TRIMMER | |||
C18 | |||||
C20 | 10PF | ||||
C26 | 470 MFD, 25V | ||||
C27 | 1000 MFD, 16V |
Transistor | Value | Note | Diodes | Value | Note |
---|---|---|---|---|---|
Q1,Q2,Q3,Q4 | BC549C | NPN transistor | D- | LED | |
IC-1,IC-2 | TA7358AP | FM Front-end IC | D- | 1N4007 | reverse polarity protection |
IC-3 | LM7805 | Voltage regulator |
Other items & hardware...
Mic
& PTT switch, Relays.
Copper
wire,20swg or similar for connecting the stages.
Copper
islands cut for placing the components
Adhesive
tube used in plumbing to join the water piples.10gm.
Fone
pins, plugs,
Aluminium
sheets to cover the entire units. Some paper for insulation.
Special
note:-
Please
make sure the Vcc is 5Volt dc .
How
many contacts I have made with this ? None,
Is
there any AM signal ? Yes there might some leakage of carrier due to
the gain stages and absence of the xtal filters.
What
development I can make ? well nothing much, in this one. if you don't
like the tuned stage, please use the resistor as load but then there
will be no harmonics filtering. This is just a simple DSB modulator.
Take it as a basis for your own design.
Can
I use the external VFO, DDS:- No need .its made for simplicity. If
you want to use vfo/dds then it will be more rewarding to make a
complete trx set of bitx.
posrasia_shi-North Las Vegas Antonio Rodriguez https://wakelet.com/wake/5KqXnSY-9ecUaaLhI1_sV
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