[Elecraft] KX3 "Full" SDR

[Edward R Cole]

I am in general agreement with what Greg writes, below (but with some 
comments inserted);

Date: Tue, 31 Dec 2013 12:38:28 -0500
From: Greg Troxel <gdt at lexort.com>
To: Don Wilhelm <w3fpr at embarqmail.com>
Cc: elecraft at mailman.qth.net, Craig Schroeder <craigs at neb.rr.com>
Subject: Re: [Elecraft] KX3 "Full" SDR

There are several important questions that could be lurking behing "full
SDR", especially since Craig talked about hobby aspects of SDR -- people
often mistakenly equate SDR with "open-source SDR", blurring "functions
are controlled by software" with "user can control functions by
software".

1) Is the modulation/demodulation done in some sort of processor under
software control, from a wide IF (perhaps at 0, perhaps higher)?  This
is the normal definition, and indeed the KX3 meets it.

2) Is the user of the radio able to change the firmwmare, in order to
experiment or for other purposes?  One might call this "user-changeable
SDR".  Here, the KX3 does not meet that definition -- while Elecraft has
released updates and improvements and can be expected to keep doing so,
users cannot improve or even read the software.

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Here I must insert a comment that commercial SDR's do not generally 
offer "open source" sw to their customers, either.  This is a special 
issue that fits one of ham radios treasured activities of being able 
to "roll your own" and redesign everything!  I would maintain this is 
a small group in ham radio (even for a tech guy like me).
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2a) Can someone who changes the firmware share their improvements with
the world?  This is a further nuance, leading to "open-source SDR".
Flex used to be like this, but I understand (from speaking to a Flex rep
at Boxboro 2012) that the software used with their radios is now
proprietary rather than open source.

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Probably Flex has learned the hard way that opening up everything to 
general access has a huge customer service headache attached!  Again 
you will not find this offered in commercial or military SDR's.
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   And, it is limited to Windows
only, which leads to an unreliable system (as described by a Flex user
who gave a talk at a local club).  Note that there is hardly any
discussion of KX3s locking up and being flaky and needing to be
rebooted.

Then there's a related question separate from SDR definitions, having to
do with packaging and interconnects:

3) Does the radio function without having to carry along an external
computer?  There is great merit in a small low-power box being
functional by itself.

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I would venture to say you will not see the military running around 
with radios that require a computer to operate - they may use one as 
an accessory like a typewriter.
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Craig:

So it really depends why you think you want an SDR.  If you want to
understand the software and contribute towards a community of people
improving it, the KX3 won't let you do that, and I would suggest that
you look at GNU Radio and other open-source projects and their
associated hardware (some of which has open designs).  If you want a
radio which has features typically achievable in SDR, and that you can
expect to be improved by the manufacturer, and you don't mind not being
able to change it (and that others can't either), then the KX3 fits the
bill.

If what you want is to experiment with code to demodulate, the KX3 is
also a good choice because it provides I/Q output.  But I know of no way
to transmit custom signals (other than soundcard modes, which generally
are viewed as below the SDR definition).

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Yes, the soundcard interface is kind of limiting but still valid.  I 
would see better interfaces coming in the future.
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My advice is to think about what you really want in terms of an
experimentation/learning platform vs. a really well designed useful
radio.  And if you are going to experiment with code, stay within the
open-source world, so that you can share your changes with everyone.

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My guess for 99% of hams the current SDR model is quite adequate as 
folks want to buy or download free sw as new stuff is developed by 
those technically able to produce it.  In that sense the current crop 
of Flex and Elecraft SDR's are fine.  SDR is a new acronym for folks 
to figure out and understand - this discussion is good for that!
Ed - KL7UW
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73 de n1dam


73, Ed - KL7UW
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