WBX notes

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WBX for use in the USRP from Ettus research. Here mostly used with gnuradio. Based on board revision 2 (WBXv2).

First bandpass filter

The TX/RX port has a lowpassfilter. It is labeled FIL1 on the simple_gdb. RX2 does not have the filtering.


CW sensitivity is -130 dBM.



max 100 mW / +20 dBm


(as controllable from GRC)

Tx gain: 0 - 25 dB (step 0.05dB)
Rx gain: 0 - 31.5 dB (step 0.5dB)
Freq range: 68.75 Mhz - 2.2 Ghz


TX gain is set by PGA0. It is converted from decibels to volts and then sent to the AUX_DAC_A. This is connected to the VSET input of the Quadrature modulator (U501 = ADL5386)

In AGC (ALC) mode the VSET is combined with output from the internal log detector, and sent to the "Voltage variable attenuator" (VVA). The control voltage of the VVA is measured with the AUX_ADC_A.

Reading the VVA controle voltage in gnuradio companion

Put the snippet below in dboard.xml in the directory .grc_gnuradio and restart gnuradio_companion.

<?xml version='1.0' encoding='ASCII'?>
  <import>from gnuradio.uhd import dboard_iface</import>
  <make>$(id) = self.$(block_id()).get_dboard_iface(); </make>
    <name>Block ID</name>
  <doc>Block ID points to a UHD USRP Sink</doc>

Create a block type "Function Probe" with the following parameters:

Variable Value Comment
ID vva
Value 0
Block ID wbx The ID as given in the 'dboard' block.
Function Name read_aux_adc
Function Args dboard_iface.UNIT_TX,dboard_iface.AUX_ADC_A
Poll Rate 1

Block "Static Text" :

Variable Value Comment
ID alc
Default value vva/0.025

Create a block type "dboard" from the category "Custom" with the following parameters:

Variable Value Comment
ID wbx
Block ID usrp_sink this is the block id of the relevant usrp_sink


Component ID
U6 MGA-62563 http://www.avagotech.com/docs/AV02-1237EN
U313 MGA-82563 http://www.avagotech.com/docs/AV02-1985EN
U502 GVA-84+ http://www.minicircuits.com/pdfs/GVA-84+.pdf
FIL1 LFCNN-2250+

to verify

From http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2013-June/006982.html:

I am wondering whether the FPGA puts the receive attenuator into
attenuation mode during transmit when the receive antenna is TX/RX. If this
does not happen, then this MGA62563 sees about 1mW of power through leakage
from the T/R switch during full-power transmit (the isolation of the switch
can be as low as 21dB), which means that it will generate about 20dBm of
output, enough to blow out the MGA82563, if we are to believe its maximum
absolute rating of 13dBm.

During full duplex operation I think that the situation is better, because
now MGA62563 sees the transmitter through two switches, or about 40dB of