trying to build a simple repeater but bandwidth is way too low

[apchar]

I'm trying to make a simlpe repeater out of an Ettus x310 and labview. There's not much to it. I made it by cobbling together pieces of the examples that came with NI-USRP.

But it works only up to an IQ sample rate of about 8 MHz. Anymore and I get underflow errors from the transmitter. It's a fast machine (HP Z420) and interface (1 Gbit ethernet.) There's no signal processing being done. So why is my bandwidth so low?

[kevins33]

Hi,

Thanks for posting to the forums! Can you please explain why you are reading and then transmitting? What is the hardware configuration with the Ettus x310? Is it in loopback?

Also, what daughter board do you have on the x310? The daughter board can be the limiting factor in terms of bandwidth. 

Is there anything that you will read from the USRP during the first call of the USRP RX VI? If not, then you also won't transmit any meaningful data. Please let me know, thanks!

[ErikL]

I recommend a few things:

1. optimize your ethernet settings by installing the manufacturer's driver and maxing out buffers

2. Build a producer / consumer architecture in LabVIEW using FIFO's, just in case there is a hickup in the windows system that would make it overflow

3. Don't transmit continuously unless a signal is present at the reciever.  Most real repeaters use a CTCSS tone for this purpose.

Cheers,

Erik

[apchar]

Thank you for replying.

Ultimately there will be some signal processing between receiving and transmitting. I just wanted a barebones system working before adding more overhead.

I dont know what the hardware configuration is or how to set it. The FPGA image is the one that came with NI-USRP.

The daughterboard is the UBX-160 so there's a lot of analog bandwidth.

There is a continuous stream of input data.

The ethernet drivers are from the manufacturer. 

Ethernet MTU is 1472. SendFastDatagramThreshold is maxed at 1500. So the buffers are as big as they can be. I've tried increasing the packet sizes in the labview code. That's how I got to 8 MHz.

I'm not sure how to implement a fifo like architecture.

Thank you,

Art

[zafarqos]

Did you try using labview queue function to get fifo functionality?