QS1-R vs SDR-14 vs Perseus -- Direct Sampling HF Receivers

Mike O'Dell mo at ccr.org
Mon Jan 25 20:15:07 CST 2010

thanks for the correction of the K3 IF frequency.
that's what I get for believing what I read on the Intardnet


On 1/25/10 12:18 PM, Tom Azlin N4ZPT wrote:
> Hi Mike,
> there is another comparison page out there told from the QS1R view.
> http://www.srl-llc.com/QS1R-vs-perseus.pdf
> in addition to http://microtelecom.it/perseus/tests/Perseus-vs-QS1R.pdf
> Perhaps both read together are useful. And the side bar in the ARRL
> SDR-IQ review on measuring performance in sampling receivers.
> BTW, the Elecraft IF frequency is not 10.7 MHz. It is 8.215 MHz.
> Filters from either Elecraft or Inrad are available. I use the SDR-IQ as
> a panadapter slaved to the K3 via the LP-Bridge software. Do not have
> the IF output mod that raises the gain on that path but it works nicely.
> And if I put a second sound card in my computer I would have two more
> demodulators to use.
> 73, Tom n4zpt
> On 1/25/2010 6:51 AM, Mike O'Dell wrote:
>> that piece was indeed interesting reading as well.
>> Nico is clearly a very sharp dude. when a bunch
>> of people started spouting about phase noise, etc,
>> he published a screen shot from an R&S source analyzer
>> showing that indeed, a rock-solid sample clock with
>> digital down-conversion has as much phase noise as,
>> well, a rock. it took a while to convince people that
>> no, there is no DDS or PLLs in the picture to make
>> phase noise.
>> the discussion on the K3 list swirled around for
>> quite some time but managed to remain far more
>> civil than i would have imagined given the vehemence
>> with which some of the doubters expressed their opinions
>> we saw a similar kind of thing when the group was
>> doing spread spectrum: people are so used to thinking
>> "narrowband" and "signal-by-signal" they cannot
>> let go of it. There is an interesting gray area,
>> though, typified by the K3, of a single-conversion
>> superhet with a reasonably high&wide IF - 10.7MHz in the
>> case of the K3 - followed by a good, fast ADC+DSP
>> to do everything from there wideband. is that an SDR?
>> or rather where does it land on a scale of 0 to 1,
>> with 0 being a classic Conrad-Johnson triple-conversion superhet
>> and 1 being a Hypres intercept receiver with a superconducting
>> front-end running at 40Gigasamples/second with a -145dB noise floor?
>> there was a rather intense discussion
>> about how an SDR could not possibly hear a signal
>> at -115dB in the presence of really loud local stations.
>> Phil finally just emailed a screen shot of 4 or 5 carriers
>> at 0dB with a tiny little spike down at -115 clear as day
>> under the display cursor.
>> as i said, the Perseus is advertised as a high-performance
>> SWL receiver, and there's just no arguing with that.
>> they really are optimized for different purposes, although
>> the "feasible regions" overlap a very large amount.
>> Phil does have a front-end board in the works which has
>> a switchable preamp (*not* in the path all the time with
>> a switchable attenuator - the preamp is bypassed) with
>> a set of "roofing" filters (aka "preselector"?) to help
>> deal with really hot local signals that drive the ADC
>> into clipping (which is at +9dBm - not a small signal).
>> that way he can just squelch the argument about front-end
>> filters, preamps, etc.
>> as for the cost, the big improvement would be to get it
>> fabbed by someone with some buying leverage. he's buying
>> expensive parts at very high prices because of no quantity.
>> and since he's decided to not take any prepayments, all
>> his working capital is coming out of his hide. very clean
>> from one point of view, but very, very painful from several
>> points of view.
>>      -mo
>> On 1/24/10 3:42 PM, Tom Azlin N4ZPT wrote:
>>> Hi Mike,
>>> Yes, interesting differences. Did you see
>>> http://microtelecom.it/perseus/tests/Perseus-vs-QS1R.pdf
>>> I looked at the Perseus at Dayton last year but in the end chose to buy
>>> a QS1R as a building block for learning. And if the other boards do come
>>> along then it may be a nice full receiver as you say. To complement my
>>> HPSDR. In the meantime a nice back end especially if I can use my GPS
>>> stabilized oscillator as an input to the QS1R and downconverters.
>>> 73, Tom n4zpt
>>> On 1/24/2010 2:10 PM, Mike O'Dell wrote:
>>>> thinking hard about how far i wish to put my foot
>>>> into the SDR pot, I've been doing a lot of reading,
>>>> trying to distinguish data from opinion from venom.
>>>> i'm recording them here to elicit commentary from
>>>> the knowledgeable chaps around the table.
>>>> if one is willing to spend a grand on an SDR receiver,
>>>> that puts one in the realm of the "direct sampling" receivers.
>>>> after comparing these three at some length (reading a lot
>>>> of extremely animated conversations, esp on the E-K3 list,
>>>> of all places), the Perseus appears to have the edge if
>>>> what you want is a full-up *receiver in a tin*. The SDR-14
>>>> seems also to be "dedicated receiver" but a bit more
>>>> bare-bones (or purist, depending on your religion).
>>>> However, if one is looking for a receiver which can be the basis
>>>> of a *platform*, then the QS1-R appears to have the edge
>>>> as it was clearly designed as such, and new companion
>>>> boards are coming along.
>>>> It should be noted that the Mercury receiver card and the
>>>> RX section of the Hermes one-board xceiver from the "OpenHPSDR"
>>>> project are essentially identical to the QS-1R.
>>>> As for sampling performance and BW (sans undersampling),
>>>> the QS1-R samples at 125MS/s and goes to 55MHz (hello 6M!)
>>>> the Perseus samples at 80MS/s and goes to 30MHz (limited by preselector)
>>>> and the SDR-14 samples at 67MS/s and goes to 33MHz
>>>> the QS1-R and the Perseus have a much
>>>> newer A/D part than the SDR-14.
>>>> That's one of the huge paradoxes in the
>>>> electronics biz - the guy who starts 6 months
>>>> after you has a big advantage because he usually
>>>> has better parts to pick from. The cellular radio
>>>> base station business is driving the evolution
>>>> of digital RF hardware really hard. The LTE/WiMAX
>>>> MIMO air interfaces assume massive digital
>>>> processing.
>>>> the other possible advantage the QS-1R and Perseus
>>>> have over the SDR-14 is that all of the DDC
>>>> processing (Quadrature NCO + Mixers + Digital Filters)
>>>> is done in an FPGA while the SDR-14 uses
>>>> a fine, off-the-shelf DDC from ADI. The QS-1R
>>>> has a very large FPGA while the Perseus seems
>>>> to have been cost-optimized (not a bad thing!).
>>>> the net result, though, is that in line with
>>>> being a platform, the QS-1R has lots of room for
>>>> further expansion of the digital processing.
>>>> (one option being explored is a true multi-channel
>>>> receiver).
>>>> In all 3 cases, the raw A/D samples
>>>> are available, as are the I/Q signals from the
>>>> DDC.
>>>> so my take is that if one were to take the plunge
>>>> for a "big bite" direct-sampling receiver intended
>>>> to be the basis for AMRAD-style geekery-hackery, the
>>>> Quicksilver QS-1R is the best of 3 quality alternatives.
>>>> again, this is my digestion of the current state of things
>>>> and the whole point of posting this is to have my
>>>> understanding improved by facts known to others.
>>>>       cheers,
>>>>       -mo
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