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# Tuning into an square wave radio transmitter

A

#### Anders Nesheim Vinje

Jan 1, 1970
0
Hello. I was wondering how to filter out a 1MHZ square wave radio signal. I
got the sender working correcly.
I am sending this as digital data to a pic controller.
My first thought was to use capacitor and a coil in paralell. And find the
high impedance frequency by using the formula 1 / (2pi * squarerot(C*L)).
Now i am not so sure. I guess this only works for a sinewave signal.
So does anyone know how to filter out any other signals below and above 1
MHZ of a square wave signal??

Thanks in advance.

Anders N. Vinje

J

#### John Fields

Jan 1, 1970
0
Hello. I was wondering how to filter out a 1MHZ square wave radio signal. I
got the sender working correcly.
I am sending this as digital data to a pic controller.
My first thought was to use capacitor and a coil in paralell. And find the
high impedance frequency by using the formula 1 / (2pi * squarerot(C*L)).
Now i am not so sure. I guess this only works for a sinewave signal.
So does anyone know how to filter out any other signals below and above 1
MHZ of a square wave signal??

---
Could you supply a little more detail, please?

1. What do you mean by a "1MHZ square wave radio signal"?

2. What do you mean by "sender"?

3. When you say that you're sending it as digital data to a PIC, do
you mean that you have the 1MHz signal connected to it directly, or
do you mean that you're sending it as a CWRF signal, or do you mean
that you're modulating a carrier with a 1MHz square wave, or ????

4. If you run the 1MHz square wave signal through either a lowpass or
a bandpass filter such as the tank (the parallel LC) you've
described, the harmonics of the square wave will be attenuated and
the output of the filter will be mostly a sine wave with the same
period as the square wave. Is that what you want?

A

#### Anders Nesheim Vinje

Jan 1, 1970
0
It is a crystal oscilator connected to the parallelport of a computer.
When i put a 5 volt high its input i generates a 1Mhz squarewave signal.
The output is conected to an anntenna. Its based on this
http://www.scitoys.com/scitoys/scitoys/computers/radio/computer_controlled_transmitter.html
3. When you say that you're sending it as digital data to a PIC, do
you mean that you have the 1MHz signal connected to it directly, or
do you mean that you're sending it as a CWRF signal, or do you mean
that you're modulating a carrier with a 1MHz square wave, or ????

The purpose is to recive the 1Mhz signal and translate to a 1 when signal
is present and 0 when not present. I do need much data transfer since it
only
is supposed to control 2 electric motors. After amplification and rectifing
(and tuning) i was thinking of using a capacitor to ground, charging up when
the signal is present so its dc componet will be close to 5 volt. And a 5,1
volts zenerdiode to limit the voltage. Then have a resistor to ground so its
allowed to charge out when the signal is no longer present.
This might be a stupid idea on how to transmit data from one device to
another but i am kinda new to this so any other suggestions would be much
appricated.
The only thing is that i want it to be simple and that only signal that can
be recived is the 1 Mhz.square wave. I guess that modulating it with a sine
signal and then
tune into that frequency on the reciver might an option to. Or if its
possible to convert the square wave to a sine signal at the transmitter
might be even better.
Well i am open for suggestions.
4. If you run the 1MHz square wave signal through either a lowpass or
a bandpass filter such as the tank (the parallel LC) you've
described, the harmonics of the square wave will be attenuated and
the output of the filter will be mostly a sine wave with the same
period as the square wave. Is that what you want?

Will this convert the square wave into a sine wave at the samme frequency??

Thank for you answers.

Anders N. Vinje

J

#### John Fields

Jan 1, 1970
0
---
That is a VERY, VERY BAD idea. Not only will the amount of 1MHz you
broadcast be very small, depending on the length of the antenna you
could be causing someone some real grief since a square wave contains
an infinite number of odd harmonics which you will also be
broadcasting. I'm pretty sure it's also illegal.
---
The purpose is to recive the 1Mhz signal and translate to a 1 when signal
is present and 0 when not present.

---
That is also a VERY, VERY BAD idea, since you'll have your antenna
radiating for God knows how long, and it doesn't sound like it's going
to be just an intermittent thing, so you could be screwing someone up,
big-time, for a long time. The FCC takes a _very_ dim view of that,
as will, I'm sure, whoever you might be screwing over. :-(
---
I do need much data transfer since it only
is supposed to control 2 electric motors. After amplification and rectifing
(and tuning) i was thinking of using a capacitor to ground, charging up when
the signal is present so its dc componet will be close to 5 volt. And a 5,1
volts zenerdiode to limit the voltage. Then have a resistor to ground so its
allowed to charge out when the signal is no longer present.
This might be a stupid idea on how to transmit data from one device to
another but i am kinda new to this so any other suggestions would be much
appricated.

---
It's not a stupid idea, it's just an idea with so many problems
surrounding it that it's not a _good_ idea. As for suggestions, if
you could give a good deal more data about what your application is
then maybe you'll get some good help.
---
The only thing is that i want it to be simple and that only signal that can
be recived is the 1 Mhz.square wave. I guess that modulating it with a sine
signal and then
tune into that frequency on the reciver might an option to. Or if its
possible to convert the square wave to a sine signal at the transmitter
might be even better.
Well i am open for suggestions.

---
Forget the RF way unless you want to buy a commercially available, FCC
approved, transmitter-receiver set designed to do what you want.
---
Will this convert the square wave into a sine wave at the samme frequency??

---
Yes, but there's much, much more to it than that.
If you really want to get into RF, then you need to go to:

http://www.arrl.org

and start at the bottom.

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