Using multiple LimeSDRs with a Thunderbolt 3 dock

Has anyone tried using multiple Lime SDRs over Thunderbolt 3 using a dock.
Ideally I want to interface to 4 LimeSDRs but most of the docks I have found only
support 3 USB3 ports.
OWC does a Thunderbolt 3 dock but at > £200 it is rather pricey. It appears to
be aimed at the Mac but one of their distributors seems to infer it will work with a
PC as well. The shipping date keeps slipping though.

  • Charles


I’ve always admired your work (especially on PC-HFDL), so let me get that out of the way first… :slight_smile:

I’m not sure of many that own more than two LimeSDRs (because of the cost), so that’s going to be a question for the heavy-duty developers out there…but I’m sure they’re out there…

73 de Marty, KN0CK

Hi Marty,

Yes PC-HFDL was pioneering in it’s day. It is getting a bit long in the tooth now though.
Not helped by Google removing support for the COM interface I use to send plots to Google Earth.

I have 5 LimeSDRs and have plans to use them for Digital beam forming. My latest PC motherboard
MSI Z270 has Thunderbolt 3 on it (40 GB/s). I just need to figure out how to use it for SDR now.

I think I will just have to wait until a suitable dock becomes available. All my PCI slots are
filled with NVIDIA Pascal GPUs otherwise I would have plugged in some USB3 PCI cards.

  • Charles

Don’t know anything about the question. Sounds like it’ll require some pioneer spirit!

One thing I miss these days are clean room type tests for these different busses and the hardware that is advertised to support the rates these devices are supposed to reach. Seems like no one hold the feet to the fire anymore.

Is thunderbolt the apple protocol? Is this the one that they recently released all the specs on?

I am curious about your application of digital beam forming. Sounds like a tx project but I have read about some stuff where they do interesting things with “digital antennas”.

Apple came up with it I believe but it is starting to appear on Windows machines
both my laptop and my desktop have Thunderbolt 3. Most peripherals are aimed at
Macs but they are starting to appear for Windows machines as well. The OWC dock I was
looking at apparently doesn’t work with Windows so I will keep looking.

I did find the Thunderbolt webpage that lists available devices.

It (beam forming) could be used for transmit but my thoughts were to use it for
receiving/tracking multiple Cubesats in the 70 cm band. The PC would grab the samples from the 4 Limes
then using pinned memory transfer them to a GTX1080TI GPU card to do the signal processing a GTX980TI
is then used to display the results. The antennas would be an array of 8 turnstile antennas.
So far I have the Limes and have built the P.C and that is as far as it goes.

  • Charles

Really nice project Charles, thumb up


do you plan to create a project, list and document on this?

It seems that these turnstile antennas are used in satcom, very interesting theory I’d guess on how to phase this array.

Sort of, there is someone selling 70 cms turnstiles on eBay

I bought one for evaluation.

  • Charles

Well I think the thunderbolt is a good idea. USB is a mess. Hardware by committee. I glimpsed a spec for some USB3 version that can handle up to 100watts. And there seems to be different USB3 specs or sub-specs or ??? Messy and look at the trouble and how long it has taken to manufacturers to get USB3 right.

Your project sounds interesting, I’m not familiar with Cubesat data. What kind do they send out?

Put it on and win some money?

####Update: There’s mention of Cubesat in the myriad blog Over The Air for June 8, 2017 and this page

Unfortunately the dock would just convert Thunderbolt 3 into a number of USB3 ports.
But I believe TB3 can be daisy chained so multiple docks could be used.

I did have a quick look to see if it was possible to get a TB3 chipset that could be
integrated into an SDR, didn’t find anything but I suspect they will come eventually.

Mind you after all the blood and toil working on the DATV-Express hardware I am
not too enthusiastic on hardware development any more especially for small volumes.

  • Charles

I have always had this dream of someday implementing a 8-element array for low bands with mini-whip receiving antennas. Nowadays with the profusion of SDRs, maybe this could be feasible at low cost:

With SDR, the delay lines can be re-configurable and simplified when compared to the analog phased arrays:

These days it is only software :sunny:

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The TB3 hub gives you 4 USB3 ports. The TB3 pc interface gives you 40GB/s and USB3 is 5GB/s so you push 20GB/s to the pc from the 4 limesdrs. Do I undertand correctly? I’d be pleasantly surprised if the hub actually worked to handle/marshall/negotiate 20GB/s from 4 devices.

No doubt they will come soon. Maybe Cypress working on it now.
Let’s hope the designers translate the spec properly and take the time to test and confirm properly.

After doing a bit more Googling I am still confused however TB3 seems to be heavily patented by Intel (basically it is their technology now).

It seems that you can connect two laptops TB3 to TB3 for high speed transfer so that seems to infer the chipsets are
bidirectional. Also Intel have bundled TB3 and USB3 in their controllers to try to get more manufacturers to adopt it.
There licensing fees were very high which put a lot of people off but I read they are going to reduce the licensing fee
so as to get more people using it.

TB3 seems to break the interface into multiple ‘lanes’
so I suspect what I was proposing will work in theory but I think I am going to have to wait!

  • Charles

I had no idea Intel was involved. Licensing fees will probably ensure its demise.

How about 10GbE? Ethernet’s well understood and there’s tons of code. Now I wonder about fiber optics? But probably a lot of money. Those globe spanning cables are doing multi-terabits/second. But I’m partly kidding. I guess it’s back to USB3.

It seems Intel will be getting rid of their licensing fees for 3rd party chip developers next year if the tech
media are to be believed.

  • C

Wait a minute, what’s PCIe bandwidth? Why not use that model? Is it because you have the boards already? Are they shipping the PCIe model now?

Yes I already have the boards, have no spare PCIe slots left and I noticed they were demoing a dual LMS7002M
PCIe card in their last video.

I guess you’ll have to find some PCIe slots for those new dualies! Have never thought of this but are there motherboards that expose the PCIe bus to allow for external PCIe expansion??? May be impossible due to timing issues.

Cabling PCIe bus is a normal practice in industrial solutions for high-demanding applications. It is a mature technology standardized by the PCI-SIG group.

The only problem is that this solution doesn’t target consumer products, meaning it is usually a low volume, high price product.

Check this out, it has a PCIe Gen2 160Gbs link:

But the price for the board alone is $3K! Despite the fact the board has two switches with 80 lanes each, this board seems to be way overpriced for our hobbyist standards. If this type of expansion board had volume production and high demand, we would buy for $100.

I would imagine filling this board with high-performance GPU cards and I would call it a super computer.

The PCIe cable is driven by this chip. PCIe Gen3 is also used.

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