[hobby] [notes] [sdr] [spam] was Re: SDR projects have been developing

Karl gmkarl at gmail.com
Sun May 2 11:39:51 PDT 2021

> I'm pretty sure you could use ICA and adaptive subsampling to make a cheap
> realtime image of your local radio environment with one of these.  Could
> also a dish antenna on the gymbal to not need ICA.  This would help enough
> in reusably describing shielded rooms that I'm still trying to move forward
> on it, after all these years.

The imu is essentially a stream of data.  The timing of this stream can be
roughly calibrated by comparing with radio and motor data. (Motor changes,
then either radio or imu changes, then the other.)

With the imu seen as a stream, we can constantly slew the motors around
regions of interest to acquire data with a high degree of orientation

Here you could train an ML algorithm around the antenna's response, but I'm
not used to that for now.

ICA is a form of blind source separation that uses matrices.  For
simplification, we bucket the imu values, each one a separate vector of
data from the radios.

The radio vectors all have holes in their data, but at first we only care
about what the sources are, not what data they are sending, so we store
each radio vector as a single FFT, averaged from all recordings in that

Now the data matrix can be seen as a single audio source, with a huge
number of "ears" each receiving a single spectrogram as their "sound".

Blind source separation (ICA, unmixing) remixes the data in such a way that
multiply recorded signals cancel each other out, producing as many clear
independent signals as their were original recording channels.

After the ICA unmixing, a matrix is produced that holds the weight of every
contributing channel.  Because this matrix is the contribution of every
angle of recording to every extracted signal, each column shows the
spherical responsivity of the antenna and cymbal setup, shifted to be
centered around each different source.

The antenna response function of angle could be extracted by aligning and
averaging all the columns.  In fact, aligning them is needed to identify
the direction of the sources.

There are a _lot_ of unaddressed concerns that will likely require some
algorithmic redesign.  It is just one approach.

But it is valuable to have the IMU data be densely available as a stream,
if possible.  It is also valuable to support continous rotation drive

Alignment of signals to calculate the antenna response or calibrate the
streams could be done by simpy looking for the maximum of the sliding
absolute difference or product.

Metrics aiding in the indication of poor data would likely be very
helpful.  Approaches like this only work in the regions of data where they
are valid.

I did not fully edit this to include further parts.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: text/html
Size: 3815 bytes
Desc: not available
URL: <https://lists.cpunks.org/pipermail/cypherpunks/attachments/20210502/b9a85c2a/attachment.txt>

More information about the cypherpunks mailing list