On Sun, Sep 4, 2016 at 9:48 AM, Gavin Jacobs <apriljunk...@hotmail.com>
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.
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