Introduction to DARS

Introduction to DARS: Distributed Amateur Radio Station

Going full digital with Ham Radio

Linux User Net topic notes for for April 1, 2019 (KC7MM, NCS)

The future is binary

Amateur Radio is going digital. With the advent of affordable digital electronics, it’s only a matter of time before analog radios disappear from retailers’ shelves, and all new rigs are based on SDR.

It’s not readily apparent now in these early days, but the move to digital means more than simply replacing a radio’s analog innards with their digital equivalents. Once an RF signal is converted to bits and bytes, it’s binary data that can be processed just like all other binary data: sent over a network, perhaps, or stored on an SD card. In fact, a ham station could essentially be a distributed computer network. In other words: a Distributed Amateur Radio Station.

A project for that

I have begun preliminary work on a project for developing a distributed station that I hope eventually could help Hams realize the full potential afforded by the digital transformation. During tonight’s net, I want to talk about where the project now, how it might develop, and of course, the role that Linux could play.

I also want to hear your thoughts about it.

Some history

A new ham

I’m relatively new to our hobby, and have been involved with SDR almost from the start. I passed the Tech exam in july 2016, and was able to get into HF the following month when I got my Amateur Extra. About that time the August 2016 issue of QST magazine appeared in my mailbox, containing a glowing review of the Icom IC-7300, a direct-conversion SDR transceiver with 100 watts output. To this old computer geek, it seemed just the thing. It wasn’t long before I was heading out the door of HRO with my first HF rig under my arm.

Limitations

The 7300 has been a fine radio for me, with many sterling features — not the least of them being its versatile filters and fine audio. But it was while investigating its potential for remote operation that I came to recognize that it has one very significant limitation: it clearly was designed to be essentially a drop-in replacement for older Icom analog rigs. It is an evolutionary advance in Icom’s product line, not a revolutionary one. Here’s why I think that:

  • It’s an entirely self-contained, standalone unit, a metal box with familiar operator controls on the front panel and the usual connection jacks on the rear.
  • Connectivity with a computer is implemented through Icom’s decades-old CI-V serial interface. It does have a USB port that allows a direct connection (plus a useful sound card) with a standard cable, but internally it functions only as an alternative to the TTL-level serial interface found on Icom analog rigs (and on the 7300). Computer control is accomplished by sending a custom set of bit strings over the serial line — identical to past practice. Icom sells its own remote-control software which is based on that, and it runs only on Windows.
  • The software that runs the rig is strictly proprietary and closed source, so the radio does only what Icom provides for. No user customization is possible.

All this is good from the standpoint of backward compatibility, but it misses out on the new possibilities opened up by being based on binary data. It does a great job on the things our experience leads us to expect a radio to do, while failing to open avenues to the new things a digital radio can do. The IC-7300 — along with its newer mate the IC-7610 — is somewhat akin to a science-fiction android: it walks and talks and looks like a traditional radio, but it’s a computer-based machine inside.

A different point of view

The lesson from all this is that, in order to understand and to realize the full potential of SDR technology, we have to step beyond our long-held conceptions of what a radio is and look at it from a fresh perspective.

The radio is…

As hams, we tend to think of a radio in terms of its functional capabilities: bands, modes, power, filters, and so on. Visually, I believe most of us picture it as a unit: a box with knobs and dials and push buttons, plus some sort of mic (or key) and a speaker.

That sounds very much like my IC-7300. In fact, looking at its front panel, you see nothing that really gives away its digital nature. To get at that, we have to turn our view inside the box to look at how it processes signals. That is, we need to understand not what it does, but how it does it. That knowledge enables us to distinguish Software Defined Radio from analog radio, and to undersand the true capabilities of SDR.

In addition, we need to look beyond the box, at how a radio fits into a radio station. That is, how it works in conjunction with antennas, mics, keys — and yes, computers — to constitute a functioning station.

Finally, we need to stop thinking in terms of electronics and electrical principles. SDR operates not in the physical realm of electricity, but in the abstract realm of data — and beyond that in the ultimate abstraction of information. For that we employ information theory.

…a computer!

With SDR, the radio is a computer, and the station is a computer system. Of course, there remain analog elements to be considered at the antenna end and in the user interface, but those are inputs and outputs at the edges of the system. Its heart is digital, and so, in designing one, we have at our disposal all the resources of the computer world.

Yes, but what does it all mean?

The upshot of all this is that a radio — and by extension, a radio station — no longer needs to be an interdependent series of stages bound tightly together electrically. Instead, it can be a collection of independent discrete components, loosely connected by binary data transferred between them: a computer network.

I see some particularly interesting implications arising from that:

  1. Since signal processing in a station can be distributed across a network, it can be performed by any computer that can be connected to the network, at any location it reaches.
  2. Computer systems are built using accepted industry-wide standards. That gives some hope of developing similar standards for distributed Amateur Radio systems.

The project

The project is still in the earliest stage of development, consisting so far of research on the current state of SDR in Amateur Radio. But there are a couple of things I know I want to do:

  1. Set up a working distributed station in my home. (Wanting a split station was the genesis of my interest.)
  2. Foster the development of voluntary standards for distributed stations that could be adopted by individuals and manufacturers to produce interoperable digital radio components and software.

I have started a section on this site that is devoted to the DARS project.


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