USRP Basics questions

GNU Radio
1

Hi All, I was wondering about some basic functions of the USRP board:

  1. To what carrier frequency does the USRP board (specifically AD9862)
    up converts the base band signal and how can we change that?

  2. At what transmission power does the USRP board transmits? and how
    that can be controlled or regulated?

  3. While using GRC, when we transmit the signal using the USRP block,
    how can we check or see the transmitted signal? Is there any pin on the
    USRP board which can be probed with the oscilloscope in order to view
    the transmitted signal.Â

Any help is really appreciated,

Thanks & Regards,
Somya A.

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2
  1. While using GRC, when we transmit the signal using the USRP block, how can we check or see the transmitted signal? Is there any pin on the USRP board which can be probed with the oscilloscope in order to view the transmitted signal.

What daughterboards do you have?

Make sure that the amplitude of the signal going into usrp sink is on
the order of 10,000 (since usrp range is +/- 32768)

-Josh

3

HI Josh, we have basic TX , RX daughter board with us. also what is that
range you have mentioned into your reply is for?

Thanks & Regards,
Somya A.

— On Tue, 14/4/09, Josh B. [email protected] wrote:
From: Josh B. [email protected]
Subject: Re: [Discuss-gnuradio] USRP Basics questions
To: [email protected]
Cc: “‘[email protected]’” [email protected]
Date: Tuesday, 14 April, 2009, 4:37 AM

  1. While using GRC, when we transmit the signal using the USRP block, how
    can we check or see the transmitted signal? Is there any pin on the USRP
    board
    which can be probed with the oscilloscope in order to view the
    transmitted
    signal.

What daughterboards do you have?

Make sure that the amplitude of the signal going into usrp sink is on
the
order of 10,000 (since usrp range is +/- 32768)

-Josh

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4

Hello,

Does anyone has some discription about the two programs usrp_fft.py
and usrp_oscope.py? I try to search in the archive but didn’t find any
basic discriptions. For example, I’m using digital-bert
benchmark_tx.py to transmit a sequence of 1’s, which modulated by
BPSK; on the other computer, I use python usrp_fft.py -f 900M -T B -R
TX/RX -d 32 to display the output.

I’ve some signals at the center frequency, but I don’t know whether it
is the signals at the transmitter side usrp or signals received in the
other usrp? Similar question to usrp_oscope.py as well, and I also
wonder what do the two lines mean, the red one and the blue one?

Thanks in advance. Your help is highly appreciated.

5

Somya A. wrote:

HI Josh, we have basic TX , RX daughter board with us. also what is that range you have mentioned into your reply is for?

Many times, users give the usrp sink numbers between +/- 1.0 and there
is no transmit power. Just to double check, you should be giving usrp
numbers around +/- 10e3 :slight_smile:

As far as how you can see the signal:

You can hook up an oscilloscope to one of the SMA connectors on the
basic TX (TXA or TXB)

Or, connect the basic RX to the basic TX with SMA to SMA connector, and
use a program like usrp_oscope.py or usrp_fft.py to look at the received
signal.

-Josh

6

Hi Josh, on the SMA connectors I had connected my transmit receive
antennas. I wanted to know if while transmitting and receiving signals
using USRP sink and source blocks, can I silmatenously probe any pin on
the transmit/receive daughter board inorder to see the signal out and in
to USRP. Also I was trying to make an OFDM system by implementing the
following blocks:

Random Source:---->OFDM Modulator:------------>USRP Sink
[Minimum=0;Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â [ Modulation:8 QAMÂ Â Â Â Â Â Â Â Â Â Â Â Â Â [Unit
Number=0
Maximum=2;Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â FFT Length=512Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
Interpolation=400
Num Samples=1MÂ Â Â Â Â Â Â Occupied tones: 200Â Â Â Â Â Â Â Â Â Â Frequency=100M
Repeat=Yes]Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â CP Length: 128Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Gain=0
                                     Pad for USRP=Yes            Â
Side=Side A]
                                     Payload length=0]

After running this, when I probed pin tx0 - tx7 on the daughter board, I
was able to see some waveforms on the scope. But when I build the
receiver system:

USRP Source:----------->OFDM DeModulator:------------>FFT Sink

[Unit Number=0Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â [ Modulation:8 QAMÂ Â Â Â Â Â Â Â Â Â Â Â Â Â

Decimation=400Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â FFT Length=512Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â

Frequency=100MÂ Â Â Â Â Â Â Â Â Â Â Â Â Occupied tones: 200Â Â Â Â Â Â Â Â Â

Gain=0 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â CP Length: 128Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â

Side=Side AÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â

RX Antenna=RXA ] Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â

I am get the following warning:
"** (python:4085): WARNING **: IPP request failed with status 1030
      Timeout "
and now if i probe the same pins on the daughter board, I am not able to
see any waveforms. Can you please help me to figure out this behaviour.

Thanks & Rgards,
Somya A.

— On Tue, 14/4/09, Josh B. [email protected] wrote:
From: Josh B. [email protected]
Subject: Re: [Discuss-gnuradio] USRP Basics questions
To: [email protected]
Cc: “‘[email protected]’” [email protected]
Date: Tuesday, 14 April, 2009, 9:57 AM

Somya A. wrote:

HI Josh, we have basic TX , RX daughter board with us. also what is that
range you have mentioned into your reply is for?

Many times, users give the usrp sink numbers between +/- 1.0 and there
is no
transmit power. Just to double check, you should be giving usrp numbers
around
+/- 10e3 :slight_smile:

As far as how you can see the signal:

You can hook up an oscilloscope to one of the SMA connectors on the
basic TX
(TXA or TXB)

Or, connect the basic RX to the basic TX with SMA to SMA connector, and
use a
program like usrp_oscope.py or usrp_fft.py to look at the received
signal.

-Josh

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7

You want to probe the SMA connectors. The pins tx0-tx7 are digital
control lines. If you see any signal on the control lines, it is
probably very weak leakage from the DAC.

Somya A. wrote:

After running this, when I probed pin tx0 - tx7 on the daughter board, I was able to see some waveforms on the scope. But when I build the receiver system:

Side=Side A

RX Antenna=RXA ]

I am get the following warning:
"** (python:4085): WARNING **: IPP request failed with status 1030
Timeout "

You can ignore this, its just wxpython molesting your printers.