Usb RTL Sdr radio with Axoloti? Plausible?

#1

Hello!

Since I am only getting started with coding, I'd like to ask some fo the more experienced programmers in this group about RTLSdr radio and Axoloti.

Do you think it would be plausible to make an Axoloti object that controls the radio?

I am not asking anyone to make it, just asking if you think it is plausible at all to make something like that for Axo?

This is the radio type:

I have been using it in Pure Data and it is really awesome tool, there is an external for it:

It would be pretty damn cool having live streaming radio into Axoloti too :slight_smile:

I did try connecting it to Axo, and the first time I got a "USB device attached" message, but didnt get it second time. So not 100% sure it accepts it or not.

What do you think?

#2

if it is an usb-audio device you are out of luck... axoloti only supports usb-midi and some other devices (mice, keyboard etc. though this is experimental/custommade)

#3

Ahh yes, that s right, USB audio not possible.

Ahh, I have it for PD, so Ill manage for now :slight_smile:

Thanks!

#4

I have been thinking about making an Axoloti based SDR receiver similar to https://github.com/DD4WH/Teensy-SDR-Rx . I would use the Axoloti stereo input for an I-Q signal pair coming from a simple quadrature direct-conversion tuner frontend. I consider making my own from a pair of SA602A mixers and a quadrature oscillator based on one of those cheap Si5351A modules. Si5351 programming code examples are available and should be portable to Axoloti.
It's a bit like a RTL dongle without the ADC and with narrower filter... Hmmm, what do you think, maybe the analog signals inside the RTL dongle before the ADC could be tapped?

#5

To be honest, I dont know that much about it, was just thinking it would a great thing to have, so I thought I'd ask more experienced guys what they thought about it. So someone else need to chip in here :slight_smile:

#6

I know little about the RTL receivers. But I think that they are not an ideal Axoloti partner, since they have a wide baseband made for digital TV. That's much data! They are so cheap because they shift almost all of the load to the PC.
I think that Teensy-SDR's schematic (in the doc PDF) looks reasonable; it should make a decent narrowband RF frontend not too much more expensive than an RTL-SDR dongle. It can even be simplified. A preselector should be added, and maybe a preamplifier.
Anyway, I think there should be some cool musical applications possible with an Axoloti radio, even without a display. I think of an automatic radio scanner / sample mangler / step sequencer or looper combination, with manual or randomized receiver tuning, for making crazy beats. Shortwave radio is full of weird sounds!

#7

Exactly my thoughts too!

Have been experimenting with this all ready in PD :slight_smile:

#8

Cool.
Really attractive to adopt it for the Axoloti world.

Hmm... in our case I'd rather invest my money in that DIY concept than in a shortwave converter for an 8-bit RTL dongle. (But I'm spoiled, having a good shortwave radio and being used to those excellent WebSDRs at my disposal...)

And...

I forgot: The Axoloti ADC would have to be made DC-coupled. (Not a problem.)

#9

Oops, I found an error in the analog part of the design I linked to. It seems to be derived from the design in http://www.hightower.com/files/Download/QEX_release.pdf , so better stick with that.

EDIT: Or maybe not an error after all? I found both variants (at least approximately) in a paper by the original inventor Dan Tayloe. (Google for "Tayloe Detector").

#10

Update:

There is a DIY shortwave SDR receiver with the same tuner frontend concept as the ones I mentioned, and using a somewhat slower processor of the same chip family as Axoloti and a very similar software basis (ChibiOS, CMSIS). So this may currently be the closest software porting candidate:
CentSDR.
Website is for Japanese audience though, and kits are out of stock.
But we would only need a minimal tuner frontend anyway, since we have the computer and the A/D converter already. A combination of the receiver module and the synthesizer module by QRP Labs might do.
This receiver technology, although cheap and performant, has the problem that it needs a filter to avoid reception on the wrong frequencies, and with this filter it is restricted to a narrow frequency band, say, a single shortwave broadcast band. If you don't mind some sound confusion, omit the filter and it will be tuneable wideband.