Re: [Discuss-gnuradio] USRP IF Receive

[Matt Ettus]

Quoting address@hidden:

> Is there an example of how to tune and demod a real signal rather than a
> complex (I/Q) stream?  I have a radio with a 10.7MHz output that I would
> like to connect to the Rx daughter card directly.

These are 2 separate things --  whether you use real or complex samples at the
IF (at the ADC) and whether you use real or complex samples at baseband (over
the USB).

You can use real IF samples simply by putting your input to I and setting Q to
0.  This can be done internally in the FPGA so that you could use 4 separate
real input.

The way the USRP FPGA code is designed, samples sent over the USB bus are always
complex.  This is not inconsistent with using real samples on the IF, since you
downconvert to 0 IF in the FPGA, and so you need both I and Q.

> Which connector is J18 or J19 is the real input?

There are muxes internally on everything, so it is arbitrary which you use.  J19
is input "0" and J18 is input "1"

> What is the full scale input power level (dBm)?

If you turn the programmable gain amplifier (PGA) down to 0 dB (the default),
then a full-scale signal would be 2 V p-p.  If you turn the PGA up to +20dB
gain, then full-scale would be .2V p-p

> What about a real transmit, rather than I/Q?

Just use only one of the outputs rather than both.

> Is it possible to populate the RS-232 driver hardware that is on each
> daughter card?  Is there still software support for it?  It would be
> useful for controlling a down converter or LNA hardware.

There is some support for it.  You could populate it, using the parts shown in
the schematic.  One thing to note -- the TXA and RXA share the same RS-232
pins, so you should only populate it on one or the other, not both.  There is a
second RS-232 on the other side, for TXB and RXB, so you could have a second
port there if you wanted.

> A note on the errors:
>
> TX d'board A: Invalid EEPROM contents
> TX d'board B: Invalid EEPROM contents
>
> You just need to run the script
>
> .../usrp/host/apps/burn-basic-eeprom

Correct.

> I couldn't find any documentation on what is stored in the EEPROMs?

The EEPROMs on the dboards basically store an identifier for the type of board,
and can store some DC offsets and the like.

> Also, there is a ./usrp/firmware/src/usrp2/burn-usrp2-eeprom script that
> writes to what appears to the be boot EEPROM on the USRP motherboard.

Yes, the EEPROM on the motherboard stores some USB info, and some very simple
code to put the board in a low power state when it powers up.  It also blinks
one LED quickly.  Once you start running anything on the USRP, a more complete
firmware (which is much bigger than the EEPROM would hold) is sent over the USB
bus.