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

[Mike O'Dell]

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


-- 
"Of course it's hard!
If it was easy, we'd be buying it from somebody else!"