On 10/06/2017 10:26 AM, Getz, Robin wrote:
Hi Marcus:
Yes – people need to understand the differences between SDR platforms
and bench equipment, it a lot more than just weight and size.
Before connecting an SDR to an amplifier – the end user needs to
understand what is really there (normally via bench equipment).
They also need to understand when they receive a signal, what’s
actually there, and what is aliasing down in the RF side. It’s a super
easy attack vector for misunderstood receivers.
Maybe I’m just too little sensitive to the noise floor – I think
there is a lot of invisible RF pollution, which is making everyone’s
lives harder, and few realize it.
I'm a radio astronomer (part-time) myself. RFI is a limiting factor
nearly everywhere these days, including sites with "dark sky" RF conditions.
When I'm doing system design, you can bet that filters play a crucial
role. They are a necessary part of an engineered RF *system*. Folks often
tend to think of SDRs as an end-solution rather than a *component* in
an overall engineered RF *system*. Many complaints about RX peformance
in particular tend to stem from this one mis-understanding....
-Robin
For those interested - there is a good article at:
https://spectrum.ieee.org/telecom/wireless/electronic-noise-is-drowning-out-the-internet-of-things
*From:*Marcus Müller [mailto:muel...@kit.edu]
*Sent:* Friday, October 06, 2017 7:45 AM
*To:* Getz, Robin <robin.g...@analog.com>; discuss-gnuradio@gnu.org
*Subject:* Re: [Discuss-gnuradio] cheap sdr platform
Hi Robin,
Yeah, I didn't mean to imply the Pluto was "worse" than others. It's
really that as you, and I thought that was really great about your
talk, showed that SDRs aren't "totally harmless toys". Indeed, I
hadn't even noticed so far the different band-specific paths of the
B2x0 were gone on the B200mini!
And yes, who am I to tell you that, but that's the price you pay for
frequency-agile SDR: Either you spend a lot of money on dedicated
filtering per band (E310, TwinRX), or you get the cheap flexibility at
the expense of selectivity. That might be the reason why an R&S
spectrum analyzer might be a tad more expensive then the average COTS
SDR device that we're considering below.
But the fact that you need your own filters, in the end, is – in my
experience – something that people building systems are very willing
to accept, because you can use one and the same SDR device that you
got to know intimately in products which you optimize for the bands
that you'll actually use in that incarnation of your system by adding
(relatively cheap) filters for exactly what you care about. That's why
it makes sense for the B200mini to lack these filters – the form
factor means it lends itself to systems integration. And that's also
why it makes sense for the Pluto to not have filters – aside from the
(extremely nice) price tag, hell, it's an experimentation platform, so
the flexibility is more important than the raw signal quality.
So, yeah, my wording was misleading there – thank you for the response!
They also have ones that are 700 MHz - 2.6 GHz (which is super
weird – since any 3^rd harmonic of the LO created internally will
mix down anything at 2100 – 2600 into the 700 – 866 MHz bands).
Well, the Ettus B200 works pretty well, but switches between the three
RX bands at 70MHz–2.2GHz, 2.2–4.0GHz and 4.0–6.0 GHz. I must admit I
always wondered which black magic was involved to support the nearly 5
(!) octaves that 70 to 2200 MHz covers on ADI's side.
Best regards,
Marcus
[1]
https://github.com/EttusResearch/uhd/blob/maint/host/lib/usrp/b200/b200_impl.cpp#L54-L60
On 10/06/2017 06:57 AM, Getz, Robin wrote:
Marcus:
It’s not only Pluto that does not have filters, I was trying to
make the point (maybe not effectively) at GRCon - it’s radios in
this “class”.
For example LimeSDR (sheet 5)
https://github.com/myriadrf/LimeSDR-USB/raw/master/hardware/plug/1v4/Project%20Outputs%20for%20LimeSDR-USB_1v4_LMS031pad/LimeSDR-USB_1v4_schematic_r7.PDF
Have Tx connectors which are spec’ed for 30MHz – 1.9 GHz – with no
filtering - my guess they will blast out the same that I was
showing – if anyone starts looking. (I haven’t got one yet, so I
don’t know for sure).
The ones that do have filters (and will not be as bad), are
limited to 2.0 GHz – 2.6 GHz; or 700 MHz - 900 MHz ; but that is
super limiting to a general purpose platform.
They also have ones that are 700 MHz - 2.6 GHz (which is super
weird – since any 3^rd harmonic of the LO created internally will
mix down anything at 2100 – 2600 into the 700 – 866 MHz bands).
What we have on Pluto is (sheet 7)
https://wiki.analog.com/_media/university/tools/pluto/hacking/plutosdr_schematic_revb.pdf
Which is the same as what we initially did on the
Evaluation/prototyping board:
https://wiki.analog.com/_media/resources/eval/user-guides/ad-fmcomms3-ebz/ad-fmcomms3_reva.pdf
Which is what was done on the miniB200 (for space saving I imagine).
https://files.ettus.com/schematics/b200mini/b200mini.pdf
These class of radios expect additional filtering on the outside
of the SMA connector. (for both Rx and Tx).
Radios which are not this that class – and can be connected in
harsh environments, or directly to amps, are like:
https://files.ettus.com/schematics/e310/e310_db.pdf
Those complex filter banks on the Tx/Rx sides are not there
because some over eager hardware developer. J
https://files.ettus.com/schematics/b200/b210.pdf
Uses 3 different baluns on the Rx side, and 2 different baluns on
the Tx side to get some frequency selectivity/filtering.
At GRCon, I was trying to make the point that just because you are
broadcasting (or receiving) at frequency X, and that looks good,
doesn’t mean you aren’t broadcasting (or Receiving) on other
frequencies at the same time (by accident, if you don’t understand
the limitations/features of the hardware). These are the specs
that folks (chip companies, or SDR manufactures) don’t talk about,
since they are hard to understand for the non-hardware person
(typically).
-Robin
*From:*Discuss-gnuradio
[mailto:discuss-gnuradio-bounces+robin.getz=analog....@gnu.org]
*On Behalf Of *Marcus Müller
*Sent:* Friday, September 29, 2017 11:47 AM
*To:* discuss-gnuradio@gnu.org <mailto:discuss-gnuradio@gnu.org>
*Subject:* Re: [Discuss-gnuradio] cheap sdr platform
Hi Ed,
as said about the general case, with the ADALM-Pluto's USB2
bandwidth, you can barely squeeze in one 20 MHz WiFi Channel if
you're using 8 bit samples, which probably won't cut it for WiFi.
For LTE: this might make more sense, but again, that depends on
the LTE bandwidth. Also, as ADI's Robin never tired to say at
GRCon: ADALM-Pluto doesn't contain sufficient output filtering, so
use at your own peril, and please don't break the law :) Other
than that, yes, indeed, looks like a pretty nice SDR!
Best regards,
Marcus
On 09/29/2017 04:23 PM, Ed Troy wrote:
I just got the Analog Devices ADALM-Pluto module. It seems
really nice, but I have not had any time to work with it yet.
It covers 325 MHz to 3.2 GHz and has transmit as well as
receive. I was one of the very few who actually got one since
Analog Devices was having some production issues. But, they
should be back on the market soon. And, as a student you can
probably get one for $99. The worst case would be $150.
Ed
On 9/29/2017 4:18 AM, w xd wrote:
Hello guys,
Have some suggestion on the cheaper SDR
platform for us to use with the GNURADIO software? As a
student, I cannot buy the expensive usrp ,but I want to
learn the knowledge by the hardware and software. Any
recommend? For example,use the hardware to do some
experiments about LTE/WIFI.
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