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Re: [Discuss-gnuradio] Optimising performance of N210 + XCVR2450

From: Michael Hill
Subject: Re: [Discuss-gnuradio] Optimising performance of N210 + XCVR2450
Date: Thu, 16 Aug 2012 19:13:11 +0930

Hi Dan,

Apologies for the delayed reply - life got in the road of my USRP stuff.. thanks heaps, these are exactly the answers I needed!!



On Thu, Jul 26, 2012 at 1:33 AM, Daniel Labarowski <address@hidden> wrote:

1) For 8 bit you change the wire format parameter of the UHD Source and Sink from "automatic" to "sc8". This is one of the options you get when double clicking the Source/Sink in GRC. Changing the output type of the block in GRC has no effect on the wire format. No modification to hardware or firmware necessary. Also, decimation would lower the bandwidth but, once again, all you have to do is change the option.

2) First off, the XCVR2450 is half duplex, so it can only transmit or receive at a time, not both. Maybe check out the SBX daughterboard if you want to do both (depends on your application, there are a few full duplex daughterboards in the ism band.) Also, remember that Ethernet has discrete TX and RX lines and each line is limited to roughly 50MSPS at 8bit, so you cant only transmit or only receive at 100MSPS.

3) It's always a good idea to terminate a transmitter as high power reflections could damage your amplifier. It's been a while since I used the XCVR and I can't remember exactly how it divided its ports. Not sure whether (since its half duplex) if it used the same port for both tx and rx by default or if they default to separate ports. You can definitely select the port when only transmitting or receiving. There is an antenna option in the usrp sink.source blocks. I've never used that option myself though so I'm not sure what type of input it expect. An integer would be my best guess so maybe start at 0 and see what you observe. If you wanted to transmit and receive on the same port you would have to stream tag the tx stream and set both blocks (sink and source) for the same port. The device defaults to receive and when it receives a tx_sob alongside the transmit signal it will switch to tx. When it receives a tx_eob, it will switch back to rx. Switching time for the xcvr is in the microsecond range. If the signals you are observing on J1 are very low power compared to those on J2, this could be poor isolation. The rf switch on the two output ports should provide 30dB of isolation. It's possible isolation on the board itself might cause some leakage too.

Good luck and I hope this helps!


On 07/25/2012 05:30 AM, Michael Hill wrote:
I have a few queries regarding some of the options for improving the performance of the XCVR2450 + N210.

1) The N210 can offer 50MSPS with 8 bit I&Q samples or 25MSPS with 16bit 1&Q.
If using 16 bit I &Q samples, I'd just leave the UHD input block with "Complex int 16".
How do I implement 8 bit I&Q (e.g. what input type do I use? and if it is 16bit.. do I have to decimate my signal in half or something? I don't need to do anything to the hardware or firmware do I?)

2) After reading further, I see that the N210 can apparently offer 100MSPS total host bandwidth with 8bit!
These seems to imply that 50MSPS refers to both transmitting and receiving simulatneously
Does this mean that if i'm only transmitting that I can thus use 100MSPS some how?

3) How do I change/set ports on the XCVR2450 or check which i'm using:
From what I read with the instructions, one shouldn't transmit unless they have an antenna or 50ohm terminator attached or it will damage the device?
I'm transmitting out of port J2 and have a terminator on J1. When I swap.. I seem to get lower power signals out of port J1?
I haven't (as far as i'm aware, done anything to change the settings... or port preference)

Does this mean that it transmits out of both ports, and one of mine is damaged?
Is it true that port J1 is the default port? in which case why are my signals coming out of both?
Do both ports offer transmit and receive, or is one port set to one function and the other port the other..

Sorry for the basic question but i've found conflicting info on the net regarding this, and still very much in the learning phase.

Thanks again gnuradio discussion list!!


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