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

Mike O'Dell mo at ccr.org
Mon Jan 25 05:19:23 CST 2010

speaking of oscillators, i remember in the dim past,
a member of this august group (Andre? Hal? Dave?) came
up with a circuit from a wizard at COMSAT for a
*synchronized oscillator*. I vaguely remember it being
like a cascode pair with the upper transistor basically
forming a pretty ordinary crystal oscillator and the
lower unit getting the sync drive. the advantage was
that it could multiply the sync drive by a remarkably
large number without the phase noise of a PLL multiplier.
(I think this came up back during the DSSS experiments.)

is that schematic around anywhere?

the reason I ask is precisely because of multiplying
a 10MHz station clock up to the QS-1R sample clock without
compromising the spectral purity of that clock.


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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