Tip:
Highlight text to annotate it
X
hi in this video I'll try
to show how to build a simple a.m.
modulator and how to test your
design. so, what you see on screen is
Tina that is a free software from Texas Instruments
and... what you see it's a simple schematic
of a quod ring
diode modulator. so, basically there're just
four Schottky diodes and a couple of
transformers and they perform the modulation
so this source that you can see
on the left here it's basically
just a carrier and and
here there is the signal that you want to use for the
modulation and here there is the output. If we go and use
function scope up this softer
you may see on output 1
there is the signal it's just triangles and
the output 2 is taken here at the
output of the modulator. let's go and see it's the signal
it is modulated so mmm
I designed the circuit
basically this way, I just added a couple of capacitors
and I've used some
software for the for the production
of some boards because most of the
components you might find are SMT
technology so you need to solder them on the boards and
you need to produce them (the boards) but I also used a
through hole board that is making it easier
to... just to
develop your circuits and... and instead for the production of
the signals I've used my spartan 3A
starter kit that it's just
a tool used for....
just for getting familiar with FPGA
the production is by
Xilinx and so I use this for this purpose
so this is the design that I decided to implement on
my FPGA here there's the input
that is the main clock, it's 50 MHz
using the digital clock manager
I generated a clock of 5 MHz and
this is the source for the other components that
are the SPI interface I used to
dialogue with the DAC (the digital to analogue
converter) that has been generating the triangles
that we saw before in Tina
this is the digital part of the triangle let's say that from here
there're bits that are going here and
this is dialoguing with
the DAC to generate the
analog output. The
two buttons (button EAST and button WEST) on board of
my board. I can choose frequency
of the triangle ( the period)
and can be greater shorter the
clock out, here, it's...
generated through the
5 MHz. The period is
multiplied per 4 that the frequency that is
going out is 5
ratio 4 so
1.250 MHz. So...
let's write now see the real
design
so, once I have downloaded the program
into the FPGA here it is
and here I may change the frequency of the
modulation via the 2
buttons I was talking before and here on the scope
we may see the the signal
modulated and the
baseband signal. I'm using a
Chinese scope that I bought for
less than one hundred dollars and
so apart from watching it on the scope
I've used a frequency
that is good for the a.m.
transmission so apart from the scope that I am going
to turn off... here I have my
old radio. Here it is
I've used..... I have used a
frequency of the the carrier of
1250
KHz
and you may hear the sound
if I'm going to change the
frequency
I may change the frequency that is
being heard
so the modulator works and
of course the load resistor
there is not and there is instead the antenna
that in my cases simply a
jumper the is used like a simple
dipole and is also not quite effective but
the main thing is that design
is working so that's all