
LimeSDR: Flexible, Next-Generation, Open Source Software Defined Radio - wolframio
https://www.crowdsupply.com/lime-micro/limesdr
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throwaway7767
What's with the male USB type-A connector at the board edge? Are users
actually supposed to plug the board straight into their computers? Seems like
a recipe to break connectors, the board is a strong lever with that length.

If that's not the idea, the more correct way would be to use one of the USB
connectors meant to be placed on cabled devices like B, mini-B or micro-USB.

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theon144
Yeah, it is quite odd. Fortunately, you can still plug it in with one of those
USB extension cords.

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gravypod
I don't know if it's me but there doesn't seem to be any tech specs. How is
the wave form generated, and is there provisioning for amps?

As a ham theres a lot of stuff SDRs do well, and interfacing with old
infrastructure isn't one of them.

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3flp
This would be okay for experimentation. It will not be able to run as a UMTS
or LTE base station or anything like that. Mostly because the software
required to do that is not available and not feasible to be done "from
scratch". Those protocols are huge and riddled with patent claims.

A minor issue would be that UMTS and LTE base stations need 0.1ppm frequency
precision (a GPS lock) which is missing here.

I wonder if the authors misrepresent their product knowingly, or if it's just
a lack of knowledge.

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throwaway7767
> This would be okay for experimentation. It will not be able to run as a UMTS
> or LTE base station or anything like that. Mostly because the software
> required to do that is not available and not feasible to be done "from
> scratch". Those protocols are huge and riddled with patent claims.

People said the same of GSM. Now we have open source implementations. It takes
a long time and it's a lot of work, and it's certainly not a given that it'll
work, but I don't share your certainty that it'll never happen (yes, I am
aware that LTE is considerably more complicated than GSM).

> A minor issue would be that UMTS and LTE base stations need 0.1ppm frequency
> precision (a GPS lock) which is missing here.

A quick google suggests 0.1ppm is what the standard specifies for "local area
BS". For a "home BS" (femtocell I guess) they give 0.25ppm.

From the datasheet of their oscillator chip (RPT7050A), its frequency
stability vs temperature is on the range +/-0.05 - +/-2.5 ppm depending on the
frequency (I didn't look at which specific accuracy it gets on the common LTE
bands).

So, you're probably right that this won't make it into commercial 4G LTE
equipment without using an external oscillator. However, I suspect this is
plenty just to get handsets to lock on to your signal for protocol
experimentation. The GSM standard has some really strict requirements for
frequency stability too, but people have made workable test networks with way
less stable equipment.

> I wonder if the authors misrepresent their product knowingly, or if it's
> just a lack of knowledge.

Lime Micro is well known, they made the RF transceiver on the BladeRF for
example. They know their stuff, so I don't think it's lack of knowledge at
least.

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robertk
I don't think the comparison on their site is fair. The Ettus B200 series uses
an Analog Devices chip that has a 640MSPS sampling rate, the Limemicro chip
can sample at 61.4MSPS at most. Even if the RF bandwidth is the same, the
Limemicro chip will have poorer performance by perhaps an order of magnitude.
So I'm not quite sure how it qualifies as next generation, even the 4 year old
HackRF has better frequency specs.

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deutronium
Are you sure you mean 640MSPS re. the Ettus B200, that sounds very high for an
entry level SDR.

Looking at the Ettus spec page -
[https://www.ettus.com/product/details/UB200-KIT](https://www.ettus.com/product/details/UB200-KIT)
they quote 61.44MS/s.

Also the HackRf isn't full duplex and the ADCs sample rate is a lot lower
however it does have a greater frequency range.

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teamster94
Throwaway to avoid giving too much away but I have used the AD9364 in a few
point to point links at my current employer. Its ADC sampling rate is 640MSPS
[1]. This oversampling is important, if not outright necessary for noise
shaping, and appropriate baseband filtering. I am not quite sure how the
LMS7002 chip can achieve a usable 56MHz channel bandwidth with only 61MSPS.

[1] [https://wiki.analog.com/resources/eval/user-guides/ad-
fmcomm...](https://wiki.analog.com/resources/eval/user-guides/ad-
fmcomms2-ebz/ad9361)

~~~
deutronium
That's very interesting I didn't realise that. So it's oversampling ~10x?

The datasheet for the LMS7002 chip seems to indicate its sample rate is 160
MHz? Which you can grab from:

[http://www.limemicro.com/products/field-programmable-rf-
ics-...](http://www.limemicro.com/products/field-programmable-rf-ics-
lms7002m/#resources)

~~~
teamster94
They are not using industry standard terms in the datasheet for some reason. I
believe the 160MHz is the analog bandwidth of the device. There is no real-
time bandwidth (RTBW/IBW) specification, which is the number the defines the
widest channel bandwidth of a device. It is likely that the 60MSPS bandwidth
can be shifted within that 160MHz analog bandwidth using the on-chip NCO to
hop around.

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madengr
Nice specs, but why are the cases so damned expensive?

OK I see $85 for the antennas and cable, but still.

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Quequau
This makes me wonder how likely users of SDRs are to run afoul of local radio
frequency interference laws.

For example I'm suspect that running an unlicensed 4G/LTE base station out in
the wild is legal (no matter what the intentions for use are).

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gh02t
I think you meant _il_ legal. Either way, I think they are mostly concerned
with signals that interfere with the normal operation of other devices. So you
could operate your 4G base station inside a Faraday cage to experiment with as
long as you're not leaking signal that interferes with anybody else.

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kseverna
"I'm suspect that" ~= "I doubt that"

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dguaraglia
Funny, "I suspect" could actually work both ways, but "I'm suspect" kind of
clears the ambiguity (but only because of usage, not because of any actual
grammatical artifact.)

English is such a crappy language sometimes!

~~~
devishard
My guess is Quequau doesn't speak American English; I've heard Brits and
Aussie's say "I'm suspect" a few times, but never Americans.

~~~
gh02t
I figured it was just an extra 'm and dropped the il, so "I suspect that... is
illegal." Haven't heard "I'm suspect" used before, but either way I guess we
know what they meant.

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wyager
Wow, this actually looks excellent if those specs are legit. A bit higher
bandwidth than a BladeRF, and wider range than the BladeRF+xb200, for about
half the price. If I was in the market, I'd probably get this.

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RachelF
No mention of RF specs, especially noise figures.

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iamcreasy
Can anyone explain in simple terms what this is for?

