[Elecraft] K3 and whats next from Elecraft

Tue Aug 20 07:50:26 EDT 2013

Ufff. You aren't EE but you have give us a great article. All point that
future is SDR DDC because issues about DDC will be covered with processing
speed improvements.

Edu yy4gmj
On Aug 20, 2013 12:58 AM, <wb4jfi at knology.net> wrote:

> Warning:  rather long reply follows.
> If you don't care, or have your mind made up, please skip this email.
>  Fred asked for some education, so here goes...  I'm not an expert, but
> these are my personal ramblings from what I think that I have learned.  If
> you don't agree, and the moderator doesn’t like this discussion here, maybe
> we can find another place to discuss?  Or directly?
>
> Elecraft has done a WONDERFUL job taming the QSD/QSE "mixers" in the KX3.
>  I LOVE MINE.  I regularly tout it at meetings, including tonight.  I think
> that I "sold" at least one KX3 and one K3 or another KX3.
>
> Having said that, the K3 and KX3 are subject to imperfections, just like
> any other analog circuitry.  Yes, the KX3 uses a QSD with "switches", but
> they have analog characteristics for an analog signal as well (on-state
> impedance, on/off switch times, off-state leakage, etc).  The op amps that
> follow them aren't perfect either.  There will be a little imbalance
> between the I and Q channels, either in amplitude or phase, due to
> component variations.  Kind of like the old phasing SSB days.  All these
> imperfections add up in a complex way, and need to be dealt with to reduce
> image issues, both on receive and transmit.  The KX3 does a remarkable job
> handling this. That's just one set of problems with "analog" radio
> circuitry.
>
> The "holy grail" of SDR is to put the ADC as CLOSE to the antenna as
> possible.  The reason is simple:  the sooner you get the signal converted
> into the digital domain (represented by numbers), the fewer imperfections
> from analog world circuitry will affect that signal.  A digital mixer just
> multiplies two numbers, for example, a "LO" represented by a set of numbers
> describing a sine wave, and an input signal, possibly from the ADC.  Within
> reason (and decent design), the numbers CANNOT change due to component
> imperfections, therefore you will not see problems with a digital version
> of a mixer, where the resulting signal is sort-of, close-to, but not what
> you want.   Two times two should always equal four, not 3.9 once, 4.1 the
> next time, etc, due to component drift, or other issues.  Filters are a
> different issue, but still more consistent and reliably reproduced in DSP
> than in the analog world.
>
> So, how can we get the HF signal right into the ADC?  That is tough,
> because the ADC itself has a limited dynamic range (and a generally poor
> noise figure).  Most SDRs use 12-bit to 16-bit ADCs, and sample from 66MHz
> to 123MHz rates.  Dr. Mitola suggests in a book that good HF reception
> requires at least 130dB of dynamic range.  IIRC 130dB works out to about
> 22-bits of ADC conversion.  16-bit ADCs by themselves provide somewhat less
> than 96dB, 12-bit ADCs provide slightly less than 72dB.  So, traditionally
> even the better SDRs needed some sort of filtering before the ADC - to
> hopefully reduce any strong out-of-band signals.  This may not work great
> on some bands, like 40M, where strong MW broadcast stations often appear
> just above or just below the ham band.
>
> There is a "trick" that is real-world, and reliable, that can improve the
> dynamic range of an ADC, called oversampling, that provides "processing
> gain".  If you sample much faster than the signal of interest's frequency,
> and decimate those samples (throw out every so many samples), you can
> achieve additional dynamic range.  I believe you gain roughly 6dB (or one
> ADC bit) every time you decimate by a factor of four.
>
> Up until recently, extremely fast and deep ADCs were too expensive for ham
> rigs, and it was hard to get more than about 20-24 dB processing gain.  The
> new Flex 6000 series has a 16-bit ADC that samples at 245Ms/s.  This allows
> them to have enough dynamic range to MAYBE not need filtering.  Notice that
> they do have filters built into the radio, that can be enabled or disabled.
> Regardless, the main analog components in the 6000 series before the ADC
> are only filters (which should contribute negligible distortion to the
> signal of interest), and a preamp, also optionally in or out-of-circuit.  I
> think even Flex has their fingers crossed regarding true dynamic range in
> the real world.
>
> Despite the comment on the Fun Cube Dongle Pro site, I doubt they have an
> actual 32-bit ADC.  Even lower-frequency ADCs, such as in sound cards, do
> not achieve that level of success.  In fact, I doubt that power supply
> noise, PC board layout, and many other factors prevent audio-frequency
> sound cards from achieving even the 24-bits that many claim.  For RF at HF
> frequencies, 16-bit ADCs are about as good as it gets - that we can afford
> anyway.
>
> Don't get me wrong, a DDC/DUC-based radio CAN have serious issues as well.
> Overload (poor dynamic range), bad noise figure of the ADC, not lining up
> the sample values right (value overflow), and a host of other issues.
> Filtering can be just as tricky (or more) in the digital domain as in the
> analog world.  And SDR hardware can be a pain to use and/or build.  Anytime
> a computer is involved, you are taking your chances.  Hi Hi.  Sometimes
> knobs are just plain easier to use.
>
> Yes, there has been a lot of discussion about whether or not the K3 is an
> "SDR".  I personally believe that it is, because a significant part of the
> SIGNAL PROCESSING is done in an executing software program, and that
> program can be changed.  Not as easily as loading a new EXE in Windows, but
> it can be.  Even though the RF front-end follows a traditional analog
> superhet receiver design up to the second IF.  In my mind, there's no
> question that the KX3 is an SDR.  It is similar in very basic layout as an
> SDR Cube, Softrock/host computer, etc, in that it uses QSD/QSE "mixers", an
> Si570, and a dsPIC back-end that is fully reconfigurable.
>
> I remember others here, including the author of much of the DSP code for
> the K3 and KX3 has previously stated that they also believe both rigs are
> SDRs. BTW, the Elecraft P3 IS A DDC RECEIVER, with a 14-bit ADC, sampling
> at about 60Ms/s, and feeding an ASIC DDC chip, then a dsPIC chip for FFT
> and other DSP work.  Yes, it samples the 8.215MHz IF from the K3, but as
> Elecraft states, it can be used on other radios as well.  It does take
> advantage of the K3's RF front end, including preamps, filtering, etc.  I
> would NOT hook an antenna directly to it!
>
> Spectrum analyzers are nice if you can afford one - many people can't.  I
> have both a homebrew W7ZOI one, and a commercial unit.  They usually don't
> have the sensitivity to look at typical weak HF signals, and they aren’t
> usually designed to demodulate anything, or at least not CW or SSB.
> Panadaptors/spectrum displays are really coming to the forefront of SDRs.
> In fact, I would argue the opposite of your comment.  Some hams are using
> SDRs, or at least hardware originally designed as an SDR, for many bench
> applications.  Spectrum analyzers, network analyzers, antenna analyzers,
> etc can be based on some of the better SDR hardware.  HPSDR Hermes, HiQSDR,
> even Softrocks, have all been used in those applications.
>
> I'm not a "digitalist", nor am I an "analogist".  I have several radios:
> RTL dongles/upconverter, K3/P3, KX3, SDR-Cube, tons of Softrocks, SDR-IQ,
> Flex 1000, SDR-Widget, SDR2GO, HiQSDR, HPSDR boardset, Flex 6500.  I know I
> forgot a couple.  I bought each for a reason, and don't disparage any of
> them.  I did finally sell my Icom IC-720a, a workhorse for over 20 years.
> Except for the clack-clacking!
>
> I've just given talks on SDRs to two local Charleston, SC ham radio clubs
> within the last week (one tonight).  I've been asked whether someone should
> buy a K3 or a Flex 6x00.  To be honest, I told them if they wanted a radio
> to "use and rely on" in the next year or so, get a K3, or possibly a KX3.
> In about a year, the Flex 6000-series MAY be mature enough to change that
> advice.  As Jerry Pournelle used to say in Byte Magazine:  RSN (Real Soon
> Now).
>
> I want to see more than just tiny little slices at a time.  For contests,
> I want to not only see how the present band looks, but hopefully multiple
> bands, so I can see how propagation is moving.  No, I'm not a very active
> contester, that's just one example.  I LOVE the K3/P3, and have used them
> on CW for Field day the last three years.  The Flex (any Flex) just isn't
> ready for that.
>
> I'm not an EE, just someone who has played with leading-edge amateur radio
> for 45+ years.  I was involved in the first licensed ATV repeater (WR4AAG),
> packet radio development, spread spectrum, a little LF, and now SDR.  I
> know how to burn my fingers with an iron.
>
> In summary: learn about Direct Digital Conversion (Digital Down
> Conversion) (DDC - whatever), look it up.  Read about it.  Don't stick you
> head in the sand, or you too may be carrying around one of those ancient
> Motorola 2M FM rigs with tubes in a Yaesu/Kenwood/Wouxun world.  There are
> definitely pitfalls to DDC/DUC radios.  But, there are several reasons why
> every "cell phone" has an SDR inside.
>
> Sorry for the length.  To each his/her own.
> 73, Terry, WB4JFI
>
> -----Original Message----- From: Fred Jensen
> Sent: Monday, August 19, 2013 3:33 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 and whats next from Elecraft
>
> I could use some education here please:
>
> What is the advantage of sampling directly off the antenna?  I'm
> surmising that's what is meant by "real SDR" vs "hybrid SDR".  I don't
> know if 32-bit ADC's existed when the K3 was being designed, but
> Elecraft settled on the hybrid superhet analog 1st IF/digital 2nd IF for
> at least one reason and probably many.
>
> The dynamic range of signal amplitudes at my coax connector across the 0
> to 30MHz spectrum has got to be huge, even after LORAN-C shut down.  Is
> there really any benefit to having that broad a spectrum with that large
> an amplitude range in the number soup?
>
> If you want to observe that spectrum, wouldn't it be better to use a
> spectrum analyzer and save your communications receiver to be optimized
> to deal with the tiny little slices we want 99.999% of the time?
>
> If the K3 sampled at the 8MHz 1st IF, after the analog roofing filters
> [i.e. RF amp and 1st mixer only], would it make the K3 a "real SDR" in
> the eyes of those who don't see it that way now?
>
> I'm serious about the "education" part, this "Is the K3 an SDR" thread
> has been going, on and off, for more than a year. It seems that we have
> two ideologies going, "Digitalists" vs "Analogists."  Unfortunately,
> debating ideologies qualitatively is rarely productive.
>
> My education is in math, my understanding of EE is the result of 60
> years in ham radio colored by a math background.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the 2013 Cal QSO Party 5-6 Oct 2013
> - www.cqp.org
>
> On 8/19/2013 11:38 AM, Arie Kleingeld PA3A wrote:
>
>  We don't have to worry about processorpower. The hardware is already
>> there and still developping. And Yes, sampling up to 6m is possible.
>> Apart from that, the interfacing from the machine to us humans can
>> certainly do better with some innovation (new ideas) as well.
>>
>
>  Op 19-8-2013 18:07, Lynn W. Taylor, WB6UUT schreef:
>>
>>>
>>> Consider for a moment an SDR with no analog filtering at all.
>>>
>>> How wide would the passband be?  Are we going to cover everything from
>>> MF to 6m?
>>>
>>
>
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