What is an SDR?

SDR – Software Defined Radio

What really is it?

Would seem that a generalized radio platform that is “made into” a radio by software is kind of the limit of the dictionary SDR concept.

As amateur radio operators we have added to that definition with concepts about software updates, sampling methods, and a whole raft of features that perhaps are neither specific to an SDR nor a requirement to meet the basic SDR definition.

Some things market expectations have added to the SDR concept is:

  • Ability to be updated by the end user, by download
  • Direct Sampling
  • Feature growth and bug correction by software updates
  • Tight integration with a computer
  • Panadaptors
  • Digital Signal Processing
  • Touch Screens
  • Remote Capabilities
  • IOT (Internet of Things) Capabilities
  • Station Integration with other station components

Updating of radios predates SDRs – many of you may remember buying a chip to add features or enhance certain radios back in the day – usually a EPROM with enhanced software on it.  Sometimes the end user could install the upgrade, and sometimes it took a trip to a technician’s bench to do it.  The delivery method of download and install also predates SDRs.

Direct Sampling is a marketplace expectation for an SDR but with many hybrid sampling methods being promoted as SDRs it doesn’t seem to be an absolute for an SDR.  There are historic direct sampling radios that are certainly not SDRs as well.

Feature Growth and bug correction go hand in hand with Updating, and plenty of historic non-SDR radios benefited from being improved and fixed this way.

Computer integration is also nothing new – some pre-SDR radios even offered dedicated PC accessories.  Others were knob-less like the Pegasus and Kachina radios, and you controlled the radio largely from a PC.  But they certainly are not SDR units.

Capabilities in vintage rigs like the Collins KM-380/HF-380 could be changed by a reprogrammed chip – does that make that series an SDR?  Not at all.

While only a fairly recent offering in the HF rig market, touchscreens are a user feature rather than something that defines and SDR.

There are some very non-SDR remote offerings, some which have been offered for years – again being able to go remote is a feature that doesn’t define whether a radio is actually an SDR or not.

I’ve seen some really neat vintage Panadaptors, so again the feature is not an SDR exclusive.

Being able to participate in the IoT is also an non-exclusive feature to SDRs.

Hams have integrated their stations from the early days onward.  Again nothing that requires an SDR.

Actually the whole list is a bunch of Red Herrings, as an SDR is all about a less specific generic hardware platform being “molded” into a particular radio through software.

Yes all ten points pulled from various online discussions perhaps are features that  many SDR share, but are not defining features:

  • Ability to be updated by the end user, by download – It is possible to have an SDR that is not field upgrade ready or use a different upgrade path than user downloads.
  • Direct Sampling – Direct Sampling is a product feature that doesn’t require the radio be an SDR
  • Feature growth and bug correction by software updates – these can be delivered by other methods including hardware updates and add-ons.
  • Tight integration with a computer – Some SDR are computerless and computer unaware.
  • Panadaptors – are available as add on features to many classes of radio.
  • Digital Signal Processing – can be added to most any radio.
  • Touch Screens – are a product feature that doesn’t require the radio be an SDR
  • Remote Capabilities – are a product feature that doesn’t require the radio be an SDR
  • IOT (Internet of Things) Capabilities – are a product feature that doesn’t require the radio be an SDR
  • Station Integration with other station components – are product features that doesn’t require the radio be an SDR

When we hear that radio XYZ and ABC is the “latest and greatest” SDR in the manufacturer’s press releases and hobby press but the actual radio is hardware-bound and cannot be reprogrammed for another use we should know we are being sold marketing marketing drivel.  In some cases the device may be partially reprogrammable but the major radio building blocks are conventional.

Then again almost ever transceiver does need some of the RF & audio building blocks to be handled at least partially by discrete conventional components.  Correct me if I am wrong but things like the FR power generation still require components we call finals, and are not reprogamable to another use.

What doesn’t come from the programming in an SDR is mostly limited to these discrete building blocks that cannot be handled another way.

Many SDRs – even if physically contained in a single package – have a server/client format to their software design.  Using a highly configurable server hardware platform the server software “defines” the exact radio configuration.  Many of the features operate in the digital world reducing the analogue radio components to only what cannot be effectively replaced by software.

The client end of the software deals with interfacing with the human end of the equation.  While it doesn’t need to have its own physically hardware, it is often integrated to the server strictly along certain lines.  Whether through defined hooks or through an open API it tends to be a separate program layer.

The SDR hardware is at least in theory redeployable in other radio configurations if programmed with an alternative definition.  Most ham radio SDRs are user level reprogrammable with updates.

Returning to the hobby marketing be careful when you read “SDR-like technology” or similar phases, as that radio is less likely to offer you the full SDR-experience or forwards opportunities.



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