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posted by
janrinok
on Sunday April 15 2018, @12:27AM
from the one-for-the-true-hackers-among-us dept.
from the one-for-the-true-hackers-among-us dept.
We’ve become used to software-defined radio as the future of radio experimentation, and many of us will have some form of SDR hardware. From the $10 RTL USB sticks through to all-singing, all-dancing models at eye-watering prices, there is an SDR for everyone.
What about the idea of an SDR without any external hardware? Instead of plugging something into your Raspberry Pi, how about using the Pi itself, unmodified? That’s just what the Nexmon SDR project has achieved, and this has been made possible through clever use of the on-board Broadcom 802.11ac WiFi chip. The result is a TX-capable SDR, albeit one only capable of operating within the 2.4 GHz and 5 GHz spectrum used by WiFi.
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The Raspberry Pi 3B+ as an SDR – Without the SDR!
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If the thunder don't get you, then the lightning will.
(Score: 2) by fyngyrz on Sunday April 15 2018, @06:01PM (1 child)
An antenna system should ideally be wideband enough to accommodate the max modulation bandwidth of the widest used modulation scheme across the RX/TX range, plus 1/2 the bandwidth of the widest symmetrical modulation scheme, or 1x the bandwidth of asymmetrical modulation schemes at one end, if you want to be able to transmit with the reference frequency right at the edge of the frequency range.
But other than that, no, you don't need different types of antennas, and you don't need filters.
For RX, what you need is enough dynamic range on the A/D system so that the sampled signal coming in from the antenna never clips. Everything else - demodulation, filtering, etc. - that can all be software.
For TX, you need a D/A with enough dynamic range to create a quality signal, and, generally speaking, you probably need an amplifier, as high-power D/As aren't exactly off-the-shelf items.
Now, it may be that the subject hardware - the wifi hardware - has built-in filtering and etc., and that could possibly interfere with some non-wifi uses of the hardware. I don't know, I've not looked at the hardware in question. But in the general case, SDR software is what handles the demodulation and modulation task.
I develop SDR software [fyngyrz.com] and have written quite a few SDR demodulators from scratch. So you can take me at my word here.
(Score: 0) by Anonymous Coward on Sunday April 15 2018, @07:12PM
You would definitely want filters at hardware level in order to focus on a particular band, otherwise your a/d converter would be overwhelmed to cover the wide spectrum the radio is supposed to be operate on.
In the end, software is limited by the hardware capacity, in this case the wifi hardware. "Software-defined" doesn't magically turn a wifi radio into something else.