Re: [Discuss-gnuradio] Fwd: Re: Transmission error

[Marcus Müller]

Hi Dave,

you shouldn't be modifying the python files before you understand what they do exactly. Please revert your edits, because it will be impossible to help you if you don't use the same scripts as we do, obviously. We've talked about this[1].

So:

Sender : benchmark_tx.py -f 2.435G -r 250k
Receiver : benchmark_rx.py -f 2.435G

That's wrong! Now, your transmitter sends 250,000 bits per second, but your receiver expects 100.000 (the default value, which doesn't work with your hardware), so that's not good. Use the same setting for both benchmark_tx and benchmark_rx.

So all you say is I need to change and play with the sampling rates and --tx-amplitude  until the received packet becomes 'n_rcvd=1'

No. RF is not "hey, there's this correct setting, let's apply it everywhere"; you'll have to figure out which combination settings work best. Generally, I'd leave the  --tx-amplitude untouched, because 0.25 is a sane value for the digital samples; what you want is analog gain, not digital scaling.

You should really set a TX gain and a RX gain. Try around with a few different gain settings for RX and TX gain -- a good approach would be to set something like 25 dB TX gain, and around 50 dB RX gain, if you place your TX and RX antennas far enough from each other. Notice that I'm assuming you're using antennas, and no direct connection! If you're using a direct cable between TX and RX, please use an attenuator, because you might otherwise damage your hardware.

To find out how to change the gains, please read the output of
benchmark_tx.py --help
and of
benchmark_rx.py --help


Best regards,
Marcus


[1] http://lists.gnu.org/archive/html/discuss-gnuradio/2015-09/msg00124.html

On 21.09.2015 16:48, Rama V wrote:

I have tried the following commands in the terminal

Sender : benchmark_tx.py -f 2.435G -r 250k
Receiver : benchmark_rx.py -f 2.435G

But the data packets are not being sent correctly. I have been receiving the packets as ok=false. I have tried modifying benchmark  python scripts. Can I do the modification of those scripts or evrything needs to be given in the command line. Please excuse me as I am slightly unable to understand. Thanks

Regards,
Dave

On Sep 18, 2015 2:21 PM, "Rama V" <address@hidden> wrote:

Thanks for the reply Michael. I will look into that as you have advised. So all you say is I need to change and play with the sampling rates and --tx-amplitude  until the received packet becomes 'n_rcvd=1' and CRC check changes to 'ok=true' from the narrowband folder?

Regards,

Dave 

On Fri, Sep 18, 2015 at 12:40 PM, Michael Dickens <address@hidden> wrote:

Hi Dave - I'm thinking that you are confusing "--samples-per-symbol" for the sample rate. I think the option you're looking for is "-r". Look at the "--help" for those examples when you get a chance. - MLD

 

On Thu, Sep 17, 2015, at 02:01 PM, Rama V wrote:

Thank you very much Michael. I will follow up on your advice. I am sorry that I wasn't able to understand some parts in GNU RADIO and didn't specify enough information.  Regarding the question, I have been doing the benchmark in the digital/ narrowband/ folder. The exact commands I have been working on are

Sender: benchmark_tx.py -f 2.435G --tx-gain 25 --samples-per-symbol 250000

Receiver: benchmark_rx.py -f 2.435G

When I give 250kS/s, my laptop freezes. USRP is XCVR2450. So I started to give less Samples like 50kS/s so that they communicate with each other without errors. But I couldn't figure out the solution to that. So I just have a doubt whether I need to modify benchmark scripts or is it enough for the parameters I give in the command line. Thanks for the help. Please advice

 

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