[Elecraft] K3 and whats next from Elecraft

Wed Aug 21 19:27:50 EDT 2013

Interesting.  My measurements up to S9+40 show it pretty linear with a 
slope of 1.001 db/SMH unit.  I didn't go above this.  I'll send you the 
curve.

The generator used is an HP8657B.  This was done with a 400 Hz filter in 
the CW mode.

73 de Brian/K3KO

On 8/21/2013 23:19, wb4jfi at knology.net wrote:
> In order to limit off-topic posts, I responded directly to Fred.
>
> One salient point is that my K3's S-meter does NOT show linear/accurate
> readings above about S9 +25.  It hits S9+60 at about -30dBm, which
> should read only about S9+40.  This could throw off the assumed dynamic
> range of 102dB.  However, Dr. Mitola's suggestion that HF needs about
> 130dB of dynamic range is still a good target, albeit tough for ANY
> radio without RF filtering (analog OR SDR).
>
> I provided several other comments, but I don’t think a manufacturer's
> reflector is the proper forum to continue the discussion.  I'm not
> hiding anything, as I think Elecraft makes at least two of the best
> radios on the market (K3/P3 & KX3), and I'm not planning to part with
> either of mine.
> 73, Terry, WB4JFI
>
> -----Original Message----- From: Fred Jensen
> Sent: Tuesday, August 20, 2013 7:50 PM
> To: Elecraft Reflector
> Subject: Re: [Elecraft] K3 and whats next from Elecraft
>
> On 8/19/2013 10:28 PM, 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?
>
> Hi Terry, thanks for the reply.  I'm thinking I'm not the only one
> seeking the education so I'll reply to the list.  If that's
> inappropriate, I'll take it off-list.  I'm also not going to quote your
> reply, those interested already have it.
>
> So far, I've learned that 32-bit ADC's have apparently not become as
> ubiquitous as I had surmised.  I have looked at the I'net SDR at Twente
> University in the Netherlands, and I understand the concept and the
> desirability of digitizing directly from the entire HF spectrum for it.
>   That cool receiver wouldn't work for everyone if it didn't.  I
> understand DSP also, or at least most of the math behind it.
>
> I want to focus my questions on a communications receiver and its
> performance however, because that's what I'm certain I don't fully
> understand.  In this focus, I'm attempting to receive a single fairly
> narrow-band HF signal in the presence of noise and other signals close
> by.  Let's say a 2KHz BW signal just for discussion.
>
> Let's say I'm digitizing at the antenna connector everything up to
> 30MHz.  We know that I have to sample at a rate at least twice the
> highest frequency being sampled so I'll stipulate that we're sampling at

> 120MHz, [4x 30MHz] and that there exists some sort of low-pass filter
> with a cutoff frequency of 30MHz, zero attenuation below, and 1,000dB
> above in front of the ADC [trying to get rid of "discussion noise" here]
>
> My K3 reads S9 with 50uV into the 50ohm connector which is 5e-11 watts,
> or -73dBm.  I have a KBPF3 [or whatever it's called] and I can find
> non-ham signals in the .5-30MHz range that will put the S-meter at or
> close to full-scale [60 over S9].  For the sake of discussion, let's

> assume the S-meter is accurate and the strongest signal I can find is 60

> over S9 or -13dBm.  Were the LORAN-C station at Middletown CA still
> operating, it would easily exceed anything I can find at HF, on my
> service monitor it generally ran around -10dBm at night with my flagpole

> as the antenna.
>
> I'll assume that the 2KHz BW signal I want to hear is S2, or 42dB below
> S9 or -115dBm which I don't think is unreasonable.  I would calculate
> then that the digitizing mechanism directly at the antenna connector
> needs to have a minimum dynamic range of 102dBm or a voltage ratio of
> 125,893 [rounding up].  2^18 gives me +/-131,072 steps so an 18-bit ADC
> should work. Right so far?
>
> In my K3, the .5-30MHz spectrum is filtered by the L-C BP filters prior
> to the first mixer, significantly reducing the effect of far but very
> strong signals on the mixer.  The 8MHz 1st IF is then filtered again by,

> in my case, a 2.7KHz xtal filter, so when this all gets to the ADC, it's

> 3KHz wide or so.
>
> And thus my first question [slightly rephrased]:
>
> "Ignoring the display possibilities of digitizing at the antenna
> connector, and concentrating on a communications receiver attempting to
> receive a 2KHz BW signal, what are the performance advantages of moving
> the A->D conversion to the antenna connector?"
>
> It seems like it should make sense to sample right at the antenna, if
> you can digitize at an adequate rate and precision, but I just can't
> make it work in my mind that subjecting the ADC to the full spectrum is
> good if I'm a single-op and all I'm interested in is the new mult.
>
> Follow-up question [watched too much 'West Wing' I guess]:
>
> Is all this "full-SDR" based on getting conversion and DSP processing
> rates high enough that it doesn't matter how far strong signals removed
> from the desired signal?  There is inevitable distortion that arises in
> the analog amplifiers, filters, and mixers, sufficiently long
> word-lengths in the DSP stages could minimize that.
>
> That's enough questions for now.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the 2013 Cal QSO Party 5-6 Oct 2013
> - www.cqp.org
>
>
>
>
>
>
>
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2012.0.2242 / Virus Database: 3211/6096 - Release Date: 08/21/13

-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2242 / Virus Database: 3211/6096 - Release Date: 08/21/13