WBX notes

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.

Sensitivity

CW sensitivity is -130 dBM.

http://www.oz9aec.net/index.php/gnu-radio-blog/319-wbx-receiver-sensitivity-in-cw

Power

max 100 mW / +20 dBm

Gain

(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

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'?>
<block>
  <name>dboard</name>
  <key>dboard</key>
  <category>Custom</category>
  <import>from gnuradio.uhd import dboard_iface</import>
  <make>$(id) = self.$(block_id()).get_dboard_iface(); </make>
  <param>
    <name>Block ID</name>
    <key>block_id</key>
    <value>my_block_0</value>
    <type>string</type>
  </param>
  <doc>Block ID points to a UHD USRP Sink</doc>
</block>

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

Components

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+	http://217.34.103.131/pdfs/LFCN-2250.pdf

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
isolation.