Transmitting gain in usrp sink

GNU Radio
1

hi community,

i wondered how the USRP is transmitting the signal even if i set the
transmitting gain to ZERO. and same as the case with receiving section.
what does setting gain in USRP sink will do ? and what is this gain
referred to? is it just to set the PGA’s gain or something different.
please help me…

thanks,
lingeswar.

2

Am 17.06.2013 19:49, schrieb lingeswar kandregula:

hi community,

i wondered how the USRP is transmitting the signal even if i set the
transmitting gain to ZERO.
ZERO is 0 dB scale…

and same as the case with receiving section. what does setting gain in
USRP sink will do ? and what is this gain referred to? is it just to
set the PGA’s gain or something different. please help me…
USRP Hardware Driver and USRP Manual: Daughterboards
Assuming you have the XCVR daughter board and the receiver end. For a
given gain setting, e.g, 50 dB, the uhd itself decides and divides the
gain between VGA and LNA.

thanks,
lingeswar.
Ankit

3

On 18.06.2013 12:49, lingeswar kandregula wrote:

hi ankit,
thanks for the reply. so, if we set a gain of 0dB, it will take it as
1 (10.^(0/10)). is it true? . and also please let me know is this gain
related to transmitting power?.
Google is your best friend!
what is the typical power transmitting from USRP.
Calibration is what you require.
http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2012-June/004783.html

Ankit

4

as you said the receiving gain is distributed between VGA and LNA. how
it
is distributed during transmission.

thanks,
lingeswar.

5

On 19.06.2013 08:35, lingeswar kandregula wrote:

as you said the receiving gain is distributed between VGA and LNA.
how it is distributed during transmission.

thanks,
lingeswar.

I think you didn’t look into the link which I have sent you previously,
so again
http://files.ettus.com/uhd_docs/manual/html/dboards.html

Ankit

6

i saw that link before… there are VGA and BB in the transmitting path
if
we consider the XCVR daughter board. is that distributed between these
two
or anything else also shares it? …

thanks,
lingeswar

7

On 19.06.2013 17:51, lingeswar kandregula wrote:

i saw that link before… there are VGA and BB in the transmitting path
if we consider the XCVR daughter board. is that distributed between
these two or anything else also shares it? …

There are only two gains (BB and VGA) that can be controlled over the
uhd interface…
Again I don’t know for what is your purpose and assuming you are using
uhd for setting gains…
You can set the BB and VGA gains values individually using the name
argument…

set_gain(uhd_usrp_source_sptr self, double gain, std::string const &
name, size_t chan=0)

double xcvr2450::set_tx_gain(double gain, const std::string &name){
assert_has(xcvr_tx_gain_ranges.keys(), name, “xcvr tx gain name”);
if (name == “VGA”){
_max2829_regs.tx_vga_gain = gain_to_tx_vga_reg(gain);
send_reg(0xC);
}
else if(name == “BB”){
_max2829_regs.tx_baseband_gain = gain_to_tx_bb_reg(gain);
send_reg(0x9);
}
else UHD_THROW_INVALID_CODE_PATH();
_tx_gains[name] = gain;

 return gain;

}

double xcvr2450::set_rx_gain(double gain, const std::string &name){
assert_has(xcvr_rx_gain_ranges.keys(), name, “xcvr rx gain name”);
if (name == “VGA”){
_max2829_regs.rx_vga_gain = gain_to_rx_vga_reg(gain);
send_reg(0xB);
}
else if(name == “LNA”){
_max2829_regs.rx_lna_gain = gain_to_rx_lna_reg(gain);
send_reg(0xB);
}
else UHD_THROW_INVALID_CODE_PATH();
_rx_gains[name] = gain;

 return gain;

}

Ankit