Daughter Boards frequencies


#1

Hello Community,

I read in the faq and in the usrp_stardard.cc that RF frequencies higher
than 44MHz can’t be tuned in URSP,
so how BasicTX, and other daughter boards can tune hundreds, thousands
of
MHz ?

Thank you all, Regards…


Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil


#2

On Wed, Jan 7, 2009 at 1:17 PM, Ronaldo N. removed_email_address@domain.invalid
wrote:

Hello Community,

I read in the faq and in the usrp_stardard.cc that RF frequencies higher
than 44MHz can’t be tuned in URSP,
so how BasicTX, and other daughter boards can tune hundreds, thousands of
MHz ?

If you are not familiar, you may want to read up on superheterodyne
receivers:

http://en.wikipedia.org/wiki/Superheterodyne

For TX, a baseband signal is mixed up to the RF signal (carrier).
Reverse for RX.

Brian


#3

Hi

I can help with the RX bit. Read up on undersampling. This is how
you would do it with a BasicRX card. You can basically sample a
signal higher than 64MHz provided that the bandwidth is less than
64MHz/2. The signal then ends up between 0 and 32MHz and is either
inverted or not. You then need to set the cordic frequency to that
frequency to mix it down to DC on the FPGA.

With the TVRX cards there is a tuner that downconverts a high
frequency signal (FM,UHF,VHF) down to somewhere below 64MHz (depending
on which TVRX revision you have).

Sebastiaan

On Wed, Jan 7, 2009 at 8:17 PM, Ronaldo N. removed_email_address@domain.invalid
wrote:

Ronaldo A. Viera Nunez


Sebastiaan H.
Radar and Remote Sensing Group, University of Cape Town
Tel: +27 83 305 5667


#4

Than you Sebastiaan and Brian, I think that I understood it now.
I’m not sure but I think cordic is not available on tx path, is it?

Thank for your answers,

Ronaldo

2009/1/7 Sebastiaan H. removed_email_address@domain.invalid

frequency signal (FM,UHF,VHF) down to somewhere below 64MHz (depending

so how BasicTX, and other daughter boards can tune hundreds, thousands of

Sebastiaan H.
Radar and Remote Sensing Group, University of Cape Town
Tel: +27 83 305 5667


Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil


#5

Sorry my ignorance, I revised my question and i was not clearly…

There is a condition on line 1008 in usrp_standard.cc code. That
condition
limits the LO frequency (see my schematic) to the maximum of 44 MHz, OK?
But
you can read in the mailing list that the baseband frequency is limited
to 4
MHz, then you are able to tx just 48 MHz (f_RX = f_baseband + f_LO = 4
MHz +
44 MHz = 48 MHz).

With my USRP using the BasicTX daughterboard I can tune my system until
248
MHz ( f_LO = 244 MHz + f_baseband = 4 MHz).

My question is: How can the BasicTX tune up to 244 MHz if the
usrp_standard
doesn’t allow to tune up it more than 44 MHz?

(Sorry my poor english, I’m learning yet…)

Thank you a lot,

Ronaldo

2009/1/7 Ronaldo N. removed_email_address@domain.invalid

Hi

on which TVRX revision you have).
of

Sebastiaan H.
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil


Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil


#6

Thank you Eric, I got it! :wink:

2009/1/8 Eric B. removed_email_address@domain.invalid

upconverter. Please read the USRP FAQ and take a look at the

  • \param db the daughterboard we’re controlling.


Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil


#7

Hi,
I am new in GNU Radio and I am trying to do some tests using the USRP
and the BasicTx daughterboard. I want to use the BasicTx to transmit at
50 MHz, but I can´t because of the 44 MHz limitation given by the DAC,
as explained in the FAQ. I´ve read about the high-level tune method in
usrp_standard.h, but I don´t know how to use it in my python program.
I´d appreciate if you could indicate me how to use this method.

Thank you!

Nadia

Ronaldo N. wrote:

Thank you Eric, I got it! :wink:

2009/1/8 Eric B. removed_email_address@domain.invalid

upconverter. Please read the USRP FAQ and take a look at the

  • \param db the daughterboard we’re controlling.


Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil


#8

On Thu, Jan 08, 2009 at 10:25:34AM -0200, Ronaldo N. wrote:

Sorry my ignorance, I revised my question and i was not clearly…

There is a condition on line 1008 in usrp_standard.cc code. That condition
limits the LO frequency (see my schematic) to the maximum of 44 MHz, OK?

No, not OK.

The code you are looking at is the code that tunes only the digital
upconverter. Please read the USRP FAQ and take a look at the
high-level tune method in usrp_standard.h

/*!

  • \brief High-level “tune” method. Works for the single channel
    case.
  • This method adjusts both the daughterboard LO and the DUC so that
  • DC in the complex baseband samples ends up at RF target_freq.
  • \param chan which DUC channel we’re controlling (usually ==
    which_side).
  • \param db the daughterboard we’re controlling.
  • \param target_freq the RF frequency we want our baseband translated
    to.
  • \param[out] tune_result details how the hardware was configured.
  • \returns true iff everything was successful.
    */
    bool tune(int chan, db_base_sptr db, double target_freq,
    usrp_tune_result *result);

Eric