Max Voltage swing for WBX boards

Hi,

I’m trying to do some signal reconstruction and in testing and
developing a
concept design, I wanted to attenuate a test signal and hook it up
directly to
the RX port of my USRP2 through either the Basic RX or LFRX daughter
board (and,
eventually through my WBX board). My intention was to attenuate the
signal
through either a resistive attenuator or inductively through a
transformer.

Essentially, I want to temporarily use my USRP2 and boards as an
oscilloscope.
I’m very aware that I need to be really careful doing this, as it
would be
very easy to break something.

Theoretically though, provided I can guarantee my signal falls within
the
accepted input voltage swing for a given daughter board, there shouldn’t
be any
problems.

A couple of questions then:

What are the absolute and preferred input voltage ranges for the RX,
LFRX, and
WBX boards?

Has anybody successfully tried this?

What are the dangers I should be looking out for?

Are there specific precautions I should be taking?

What is the best way of attenuating the signal?

Warm Regards,

V

On Tue, Sep 14, 2010 at 9:24 AM, Vincent W [email protected] wrote:

very easy to break something.

Theoretically though, provided I can guarantee my signal falls within the
accepted input voltage swing for a given daughter board, there shouldn’t be any
problems.

A couple of questions then:

What are the absolute and preferred input voltage ranges for the RX, LFRX, and
WBX boards?

BasicRX or LFRX can take +10dBm (~2Vpp)

WBX input power should not exceed -10dBm (~0.2Vpp)

Has anybody successfully tried this?

What are the dangers I should be looking out for?

Are there specific precautions I should be taking?

What is the best way of attenuating the signal?

Mini Circuits makes a line of coaxial attenuators which can be
installed in your SMA cabling, we find they work fairly well. I have
also found the the North Hills baluns to be very nice, as well as
those from Mini Circuits.

Jason

those from Mini Circuits.

Jason

Thank you for your advice. I got everything working nicely, and just
wanted to
confirm those values as working nicely.

I ended up using a simple resistive attenuator (made of discrete
components) to
ensure the signal was within the limits set above, and so didn’t have a
didn’t
have a chance to test the coaxial attenuators you recommended. Having
said that,
I’m in the processes of buying some now.

Thank you for your help,

V

On 09/14/2010 01:29 PM, Marcus D. Leech wrote:

WBX boards?
the damage level, you end up with distortions caused by clipping, and driving
stages into

Make sure that you don’t inject too much power is the main thing.

What is the best way of attenuating the signal?

Standard resistive attenuators–you can buy them ready-made in a whole bunch of
different attenuation ranges, or build them yourself with connectors/discrete
resistors.


Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

I had an opportunity to test this out, and everything worked out quite
nicely. I
made a resistive attenuator using discrete resistors, and kept the
voltage swing
to .15Vpp for the WBX, and 1Vpp for the LFRX board.

It worked quite nicely, and allowed me to save the signal to a file
where I was
later able to process it using octave.

Everything seems to have checked out, so I’m pretty sure I didn’t break
anything, and I didn’t notice any signal clipping.

Thank you very much for your help,

Vvv

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