LimeSDR: Flexible, Next-Generation, Open Source Software Defined Radio | Hacker News Reader

LimeSDR: Flexible, Next-Generation, Open Source Software Defined Radio

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98 pointswolframio28 comments

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.

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

> like B, mini-B or micro-USB [or C]

Maybe that is exactly the reason to go with type-A, i.e. to make a statement about too many different B types?

Still a recipe for a disaster of course.

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.

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.

> 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.

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.

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 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.

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...

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-...

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.

Could you elaborate on why oversampling is important? With Nyquist I was generally of the impression that 2 x bandwidth should be just fine, but in practice oscilloscopes (just one example) seem to have five times or more sampling rate than bandwidth.

The Nyquist rate is the theoretical minimum that allows you to distinguish one frequency from another. Sampling a higher frequency will cause an alias component to appear. This means that in practice, there must be analog band-limiting before the signal is sampled to reject any out of band signals before they are aliased to an in-band frequency and cannot be removed. The closer the band limiting cutoff comes to the nyquist frequency the more extreme the roll-off requirements for this band-limiting. Oversampling relaxes the band-limiting requirements, and can also increase the bit depth at lower sample rates. See PDM microphones for an example where this is taken to the extreme.

As a happy owner of a HackRF, I can say that this is better than the HackRF in basically every way other than the 5GHz band coverage. They have the advantage of producing their own custom chip, unlike the HackRF. To offer this at the same price point* seems pretty "next-gen" to me.

*Kickstarted HackRF One was $275 with case, Lime is $300 without a case and $500 with so it's still a bit more expensive.

I'm pretty glad to have jumped on one the 199$ early birds... though I'm not entirely sure what I intend to use this for.

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

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

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).

I think you meant illegal. 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.

Well, I'm glad you guys figured out what I meant, despite my lousy grammar and lack of proofreading.

I have my eye on this project for autonomous drone command & control, so operating the device inside a Faraday cage to prevent leaking a signal that might interfere with others would defeat my purposes.

I suppose the correct design would be to use two (one for the base station and one for the device) so that some other part of the RF spectrum could be used instead.

You could always try XBee. The XBee Pro modules are a bit expensive (~$50 each), but they can reach up to 15 miles or more, albeit at fairly low baud rates. The Pro-900 XSC ( https://www.sparkfun.com/products/11634 ) can stretch up to 28 miles with just its wire antenna. There's also LoRaWAN, which is even longer range but still low bandwidth and $$.

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

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!

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.

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.

Thanks for the translation; that particular idiosyncratic usage defeated me.

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.

No mention of RF specs, especially noise figures.

Can anyone explain in simple terms what this is for?

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