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El cheapo SDR

neuromodulator

I've been playing a lot with my FPGA lately, its such a fun toy! I'm currently trying to participate in the computer vision/computer graphics Project14 with it, but got a bit sidetracked to test something different. As FPGAs can read or generate very fast signals, they are used a lot in higher end SDRs. Usually you would use the FPGA with ADCs, DACs, transceivers, mixers, PLLs, filters, antennas, and what not! But when you are an "el cheapo" you don't need any RF gadgets, just the plain FPGA board to program it and let its tiny pins act as crappy antennas!

 

So I fed a 440 Hz test tone into an NCO, and let the magic happen:

 

image

 

And it sounds pretty good!

 

UPDATE:

 

I made a few modifications and now it can be used to transmit Morse (which I really don't know).

Here is a demo, left button turns the transmitter on/off, right button sends 750 Hz, ~150 kHz bandwidth FM modulated pulses.

 

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  • in reply to 14rhb

    Yes I could use other frequencies too, the FPGA board doesn't come with any RF facility, I'm just switching pin voltages from 0 to 3v3 quickly with specific patterns to generate the desired RF signal. The limitation is that I'm using a 240 MHz clock for this, so by nyquist I could generate signals between 0 and 120 Mhz. But since the signal is very "squarish" its got many harmonics, so I could use the harmonics to generate signals at frequencies higher than 120 Mhz. The reason that I'm using 106.1 Mhz is because where I live there are no strong FM signals in that frequency. Now in terms of bandwidth I could use as much as I want.