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Re: FM Transmission with a vector of bits

From: Adrian Musceac
Subject: Re: FM Transmission with a vector of bits
Date: Sat, 04 Jul 2020 07:17:17 +0000

Hi Anthony,

It's not clear to me if you are trying to implement an FSK transmitter for data or an FM transmitter for audio with the samples coming from another application. If you can clarify, perhaps I can be of some help.


On July 3, 2020 3:56:26 PM UTC, "Anthony B." <anthonyld508@gmail.com> wrote:
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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