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.
-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:address@hidden
Sent: Friday, October 06, 2017 7:45 AM
To: Getz, Robin <address@hidden>; address@hidden
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 3rd 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 3rd 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
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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