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Re: FM Transmission with a vector of bits

From: Anthony B.
Subject: Re: FM Transmission with a vector of bits
Date: Fri, 3 Jul 2020 17:56:26 +0200

Hello Kevin,

Thanks, your link had useful information about the principles to consider with a vector source.

Considering the following generic flowgraph : Vector Source > Repeat > Multiply (with a sine wave) > Resampling / Filtering > Output (?)

I have seen that most of the variables are related to the Morse code transmission with the words per minute. However, I was wondering about how to tune the interpolation rate of the Repeat block after the Vector source for a known bit sequence, but out of the Morse standard. I would also expect some kind of periodic signal, if not an audio signal, at the input of the FM transmitter (I guess). What would you expect as a clean signal at the input of the FM transmitter (output here), if not an audio signal ?

I am also wondering about how to set the cut off frequency and transition width of the low pass filter in these flowgraphs. Is it by hand, or is there a relationship with the flowgraph variables ?

Thanks for your feedback!


Le jeu. 2 juil. 2020 à 18:39, Kevin McQuiggin <mcquiggi@sfu.ca> a écrit :

Whoops!  Here is the link!

On Jul 2, 2020, at 9:36 AM, Anthony B. <anthonyld508@gmail.com> wrote:


Thanks for the answers!

Is it this project ?

I'm gonna check it out, but it looks like the idea is in there, thanks!


Le jeu. 2 juil. 2020 à 18:21, Alex Humberstone <alex.m.humberstone@gmail.com> a écrit :
Hey Kevin, I don't see the link that you mentioned, did you forget to include it?

On Thu, 2 Jul 2020 at 11:18, Kevin McQuiggin <mcquiggi@sfu.ca> wrote:
Hi Anthony:

Check out this link.  The author is using a Pluto but he developed a flowgraph to transmit a vector that represents Morse code.  Pretty well-explained.  The ideas you need are likely in there.


> On Jul 2, 2020, at 8:40 AM, Anthony B. <anthonyld508@gmail.com> wrote:
> Hello all,
> I am trying to build a very simple FM Transmitter using a flowgraph as a reference. The principle is the following :
> Signal source of 48 kHz Sample Rate >  Rational Resampler up to 360 kHz Sample Rate > Add Constant 1 > VCO at 360 kHz with a carrier frequency at 120 kHz.
> What I am trying to do right now is to replace the signal source with a vector of bits coming from another application to then modulate it with FM.
> I've seen many examples of this kind of transmitter with audio input, but I don't understand how to pass it a vector of bits and to get the expected result.
> Is there something I should consider before going to the VCO ? Is the principle only working with periodic signals as input ?
> Thanks for your help!
> Anthony

PhD Student
Klipsch School of Electrical Engineering
New Mexico State University
Las Cruces, New Mexico

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