[Discuss-gnuradio] Fw: Signal Source - frequency control

[Gavin Jacobs]

Thanks Kevin - that helped me move forward. You answered the question and then provided the answers to two more!

I used an embedded python block to take the binary bitstream and choose the right frequency for the VCO.

Now here's the frustrating part, when I tried to use another embedded python block to implement the bit banger, I got confusing runtime errors indicating that the top block was getting the two blocks mixed up(e.g. size mismatch). Is there a limit of one embedded python block?

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From: address@hidden <address@hidden> on behalf of Kevin Reid <address@hidden>
Sent: September 4, 2016 12:38 PM
To: Gavin Jacobs
Cc: address@hidden
Subject: Re: [Discuss-gnuradio] Signal Source - frequency control

 

On Sun, Sep 4, 2016 at 9:48 AM, Gavin Jacobs <address@hidden> wrote:

 I am building an application to send an APRS message. I have GRC 3.7.9.2 running on Windows 10, with a Hackrf as the radio. I have a kluge to transform the bits into an audio signal at 2200 Hz for a 0, and 1200 Hz for a 1. See the attached. But, on the Signal Source block, on the left hand side, is a grey attachment point that appears to be an input. If I hover the mouse over that, it says 'freq', but every time I attach something, it will attach but is always flagged in red (error). So, is there a way to attach a signal there and vary the frequency using the output of another block?

Gray ports are message ports — they can only be connected to other message ports, and aren't appropriate for transferring samples or bit streams.

What you want is the VCO ("Voltage"-Controlled Oscillator) block. (There are other ways to produce this sort of modulation, but that block will make the most sense getting started.)

You will also want to use a Repeat block to stretch your bits out to the appropriate length (sample rate divided by modulation baud rate) before putting it into the VCO.