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threeme3 | 4 years ago | on: Design of a Scalable 4G Portable Network Using Low Cost SDR and Raspberry Pi

Unfortunately the article does not provide an explanation how the GPIO transmit function was achieved, but most probably it was based on prior art here:

It started with piFM [1] where the possibility was explored to modulate the internal PLL Raspberry Pi with FM and output it on pin GPIO4. This was then further refined and a PWM phase and amplitude modulation technique was applied which made it possible to generate SSB signals [2]. Based on this rpitx [3] was then created which made it possible to basically modulate any type of signal, enabling to use a raspberry pi for analog and digital broadcasts, and to replace key fobs for RF smart plugs and other wireless devices. So yes, it is possible..

[1] GPIO4 piFM transmitter, by Oliver Mattos and Oskar Weigl http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspb...

[2] Direct SSB generation by frequency modulating a PLL, by Guido http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll...

[3] Universal I/Q TX for rpi, Evariste Courjaud, https://github.com/F5OEO/rpitx

threeme3 | 6 years ago | on: MBONE: The Multicast Backbone (1994)

Good memories. In 1994, about 5 years later after Steve Deering published RFC1112, IP multicast got implemented in our Dutch spanned amateur packet radio network [1]. There were about 20-30 network nodes acting as Local Access Points for access to users, and interconnected via interlinks. The nodes implemented the AX25 packet radio protocol with rates of 1200-9600 baud, on top of that you could transport IP datagrams hence these nodes were part of the 44.0.0.0 AMPR.ORG Internet network. There were nodes that had an Internet gateway through a local origanisation or university, but these gateways were mainly used to support linking the subnet of the 44.0.0.0 network and connecting the AX25 networks (via AXIP and wormholes).

The nodes here in the Netherlands used the multicast to distribute link information and IP autorouting. It was very well possible to join a multicast group somehwere in the network by multiple parties, and then stream UDP frames accross the network.

A very fun experiment at the time was to send CELP-compressed (1-2kb/s) audio packets through the multicast network, and hence it was possible to have conversation with multiple people spanning a distance larger then the radio horizon. The latency and packet loss were disrupting good operation, but it more or less worked.

[1] https://www.jj1wtk.jp/nos/history.html

threeme3 | 6 years ago | on: Fast inverse chirp z-transform found

It enables applications with spectral frequency components that are not constrained to have fixed magnitudes but also could decay or grow exponentially.

I think this exponential decay or growth is the major difference compared to an IFFT, and hence the algorithm can work more efficient over a larger time/frequency domain.

Think of improvements anywhere FFT is used today, but where there is a need to work over a non-linear time/frequency domain.

threeme3 | 6 years ago

Wondering what the reason is behind the reverted USB connector?

threeme3 | 6 years ago | on: The Most Dangerous Writing App

This is a solution to my problem: as writing for me is always a struggle due to the tendency to keep more focussed on optimizing previously written text then on continue writing new. This app allows me to write like a flow.

threeme3 | 6 years ago | on: Show HN: Bashfs – Run commands as your filesystem

microfs looks interesting to me, but unfortunately crashes with a SEGFAULT on Ubuntu 19.04:

Program received signal SIGSEGV, Segmentation fault. 0x00007ffff7de88b8 in __GI__IO_fread (buf=buf@entry=0x7fffffffd4f0, size=size@entry=1, count=count@entry=1024, fp=0x0) at iofread.c:35

threeme3 | 7 years ago | on: IPFS Project Roadmap

Exactly this: such an ultralight, accessible implementation would make it better suitable to run on embedded devices and mobile phones. And since we still live in as fairly disconnected world this is probably an area where IPFS can accelerate.
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