K3 & ADAT ADT-200A by HB9CBU
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Re: K3 & ADAT ADT-200A by HB9CBU
 
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On Thu, Dec 4, 2008 at 2:23 PM, Bill W4ZV <[hidden email]> wrote:
> > Nico, this is truly exceptional phase noise performance! My sincerest > congratulations to you. Have you described how you achieved this somewhere? > > 73, Bill W4ZV > Not to speak for Nico, but direct sampling SDRs use a crystal oscillator for the ADC encode clock which obviously can be built to have very good phase noise. The LO generation and mixing is all done in the digital domain in the FPGA so there is no degradation of the crystal oscillator's original phase noise specs. This is not always the case for DDS/QSD based SDRs due to reasons described earlier. 73 Phil N8VB _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K3 & ADAT ADT-200A by HB9CBU
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In reply to this post by Julian, G4ILO
On Thu, Dec 4, 2008 at 1:54 PM, Julian, G4ILO <[hidden email]> wrote:
> > >> The one of the interesting things about using personal computers for SDR >> is >> imho that generally more people can take part in their development in >> major >> or minor ways. This is why I just recently decided to purchase the QS1R > > I can understand the attraction of that for hams, just as I understand the > attraction of Linux for people interested in what makes computers work. But > from what I have seen of open source type development the old adage about > too many hands can spoil the broth come to mind. Like anything designed by a > committee, it can take ages to get anything done. There is a lot to be said > for having things developed exclusively by a dedicated and focussed team, as > in the case of Microsoft. > In reality, most open source SDR software is primarily done by one or two people, unlike more ambitious projects (by orders of magnitude) like the Linux OS for example. This is about as focused "team" as you can get. As a result, bugs are fixed and features are added very quickly (sometime within hours of the bug being reported). 73 Phil N8VB -- Phil Covington Software Radio Laboratory LLC Columbus, Ohio http://www.srl-llc.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K3 & ADAT ADT-200A by HB9CBU
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In reply to this post by Julian, G4ILO
On Thu, Dec 4, 2008 at 1:54 PM, Julian, G4ILO <[hidden email]> wrote:
> I was really more concerned with what support there will be for the current > generation of SDR radios in, say 10 years time. If the PC that runs the > current software dies, and you can't get a new PC that runs XP (or whatever > you need to run that SDR software) what guarantee do you have that any > software that runs on Windows 2020 or whatever will support the 10 year old > box. The manufacturer (if they are still around) will probably have no > interest in supporting obsolete products. This is one of the arguments in favor of the open source model. If the manufacturer of hardware that uses proprietary software/firmware goes away, you are pretty much stuck with whatever the last release was before the manufacturer went belly up. If the software/firmware is open source, the hardware can still be supported long after the manufacturer has gone. Of course if you can't do the software/firmware yourself, it is a little less convincing argument at face value but you always still have the option to pay or barter for a software developer to make the changes or fix the bugs that you want. With interfaces such as USB (the new upcoming USB 3.0 is backwards compatible with USB 2.0 and USB 1.1) or Ethernet, support for those interfaces in the PCs should be around through multiple versions of Windows/Linux/OS?. 73 Phil N8VB -- Phil Covington Software Radio Laboratory LLC Columbus, Ohio http://www.srl-llc.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Bill W4ZV
Phil and Chen,
Thanks! I thought it looked like crystal filter performance but was thinking it was synthesized. This looks like a much better system than Flex's QSD. I wonder how long it will be before Flex goes to the same system? Phase noise and BDR have been Flex's weak links IMHO. I just located the Perseus user manual so will do some reading on it. For anyone interested: http://microtelecom.it/perseus/perseususermanual-en12.pdf 73, Bill On Thu, Dec 4, 2008 at 3:30 PM, Kok Chen <[hidden email]> wrote: > > On Dec 4, 2008, at 11:23 AM, Bill W4ZV wrote: > >> Have you described how you achieved this somewhere? > > > Bill, > > I suspect it is because there is no synthesizer in his receiver. Everything > comes off of a single crystal, and as you decimate, the noise from the > oscillator becomes even narrower. > > All the other "oscillators" are numerical and can be made as noise free as > there are processor cycles. Even in cocoaModem (2.4 kc passband digital > mode stuff for the Mac OS X), I had use a 24 bit since/cosine generator, > using 12-bit table lookups and the double angle trig formula to get 24 bits > of output resolution. > > "Phase noise" is a hardware artifact :-) :-) > > Vy 73 > Chen, W7AY > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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On Dec 4, 2008, at 1:06 PM, Bill Tippett wrote: > This looks like a much better system than Flex's QSD. For single signal use, I agree completely Bill. By the time you've matched the sampling rate of a direct SDR to a signal with 500 Hz bandwidth, you have adequate dynamic range. (And not need the expensive Asahi codec that is used in the Flex 5000, to boot.) However, the QSD based SDRs still has a dynamic range advantage when you want to demodulate (think CW skimmer for RTTY) multiple signals in a wider bandwidth, say 50 kHz. With added complexity, you can of course implement multi-rate filter banks with direct SDR and stitch the result back together to create a wider bandpass. Toby had earlier suggested multiple direct SDRs, and polyphase and multi-rate decimation is just one way to do it (i.e., use the same RF chip, the rest is "just software" HI). We can leap frog one another until the cows come home. Moreover, that is not to say that the QSD guys can't put a "roofing" filter between their quadrature mixer and the A/D converters (just that they are not doing it today) to get even better BDR than they are getting today. This QSD "roofing filter" would just be a matched low-IMD LPF pair for the I and Q channels. A 500 Hz "roofing filter" would reduce unwanted large signals from clipping the A/D converter and can raise the 2 kc separation BDR of the 500 Hz receiving system to something that is just a function of the dynamic range of the QSD itself. It is funny to imagine a "roofing filter" that is centered at DC, but its function is no different from the crystal roofing filters in superhets. Instead of preventing out of band signals from reaching the I.F. amplifiers, you prevent them from reaching the A/D converter :-). 73 Chen, W7AY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by dj7mgq
Can we end this thread? It seems to have drifted away from Elecraft. I, and I believe others too, could care less about all these numbers and the discussions surrounding them.
Dave N8AG _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: K3 & ADAT ADT-200A by HB9CBU
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In reply to this post by Kok Chen
> Moreover, that is not to say that the QSD guys can't put a "roofing" > filter between their quadrature mixer and the A/D converters (just > that they are not doing it today) to get even better BDR than > they are getting today. > > This QSD "roofing filter" would just be a matched low-IMD LPF > pair for the I and Q channels. A 500 Hz "roofing filter" would > reduce unwanted large signals from clipping the A/D converter > and can raise the 2 kc separation BDR of the 500 Hz receiving > system to something that is just a function of the dynamic range > of the QSD itself. Unfortunately, as soon as they put matched 3 KHz or 5 KHz LPFs between the quadrature detector and the A/D converters they lose panoramic operation and have to go back to a knob or some kind of scroll tuning instead of "click on the blip." That is unless they do two sets of detectors ... a low dynamic range ADC with no filters for panoramic tuning and a high performance ADC with "roofing filters" (perhaps even selected by mode) for high dynamic range single signal use. Hardware AGC, if needed, could be derived from the high performance decoder. 73, ... Joe, W4TV > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Kok Chen > Sent: Thursday, December 04, 2008 5:21 PM > To: Elecraft Reflector > Subject: Re: [Elecraft] K3 & ADAT ADT-200A by HB9CBU > > > > On Dec 4, 2008, at 1:06 PM, Bill Tippett wrote: > > > This looks like a much better system than Flex's QSD. > > For single signal use, I agree completely Bill. By the time you've > matched the sampling rate of a direct SDR to a signal with 500 Hz > bandwidth, you have adequate dynamic range. (And not need the > expensive Asahi codec that is used in the Flex 5000, to boot.) > > However, the QSD based SDRs still has a dynamic range advantage when > you want to demodulate (think CW skimmer for RTTY) multiple > signals in > a wider bandwidth, say 50 kHz. > > With added complexity, you can of course implement multi-rate filter > banks with direct SDR and stitch the result back together to > create a > wider bandpass. Toby had earlier suggested multiple direct > SDRs, and > polyphase and multi-rate decimation is just one way to do it (i.e., > use the same RF chip, the rest is "just software" HI). We can leap > frog one another until the cows come home. > > Moreover, that is not to say that the QSD guys can't put a "roofing" > filter between their quadrature mixer and the A/D converters (just > that they are not doing it today) to get even better BDR than > they are > getting today. > > This QSD "roofing filter" would just be a matched low-IMD LPF > pair for > the I and Q channels. A 500 Hz "roofing filter" would reduce > unwanted > large signals from clipping the A/D converter and can raise the 2 kc > separation BDR of the 500 Hz receiving system to something that is > just a function of the dynamic range of the QSD itself. > > It is funny to imagine a "roofing filter" that is centered at > DC, but > its function is no different from the crystal roofing filters in > superhets. Instead of preventing out of band signals from reaching > the I.F. amplifiers, you prevent them from reaching the A/D > converter :-). > > 73 > Chen, W7AY > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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