Do I offset tune with the xb200?

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dglatting
Posts: 3
Joined: Mon Apr 20, 2015 8:24 pm

Do I offset tune with the xb200?

Post by dglatting » Sat Feb 27, 2016 2:57 pm

I have a GNURadio flow graph (recent git pull) with a HackRF One as the source and a BladeRF x115 as the sink with an x200 to transmit in the 131MHz range. The purpose of the HackRF One is it came first. I am trying to transmit a signal within a screen cage to debug my blocks.

I have an RTL SDR within the cage running GQRX. It indicates nothing is being transmitted by the bladeRF. I have instrumentation that indicates packets are going to the bladeRF. A couple of questions come to mind.

1) I see nothing in the documentation that indicates I need to offset tune when using the xb200. Is that true?

2) Does the Rx side of the bladeRF need to be active in order for the Tx side to work?

3) What verification mechanism is available to indicate the bladeRF is transmitting? An LED, perhaps?

My configuration string in GNURadio is:
bladerf,xb200=144M,verbosity=info,fpga=/usr/local/share/hostedx115.rbf

My default VG1 setting is -25 and VGA2 is 5.

TIA

jynik
Posts: 455
Joined: Thu Jun 06, 2013 8:15 pm

Re: Do I offset tune with the xb200?

Post by jynik » Thu Mar 03, 2016 6:46 am

Hi there,

I suspect the issue is your VGA1 setting. See below.
dglatting wrote: 1) I see nothing in the documentation that indicates I need to offset tune when using the xb200. Is that true?
Correct. You do not need to offset tune. When you request a frequency, libbladeRF takes care of turning that into an offset from the IF. If you tune back into the bladeRF's normal tuning range, then this IF is not used and the LMS6002D is tuned as it normally is.
dglatting wrote: 2) Does the Rx side of the bladeRF need to be active in order for the Tx side to work?
No, the two paths can be used independently of one another.
dglatting wrote: 3) What verification mechanism is available to indicate the bladeRF is transmitting? An LED, perhaps?
The LEDs show the state of the RX Overrun, scaled-down PCLK, and TX overrun, so no, these cannot be used to indicate the TX is active.

You can verify that all is well along the path from the FPGA to the LMS6002D and back using the loopback flowgraph with the rf_lna1 and rf_lna2 modes. You could then use an attenuator and tie TX to RX to further confirm that you're receiving the TX'd signal.
dglatting wrote: My configuration string in GNURadio is:
bladerf,xb200=144M,verbosity=info,fpga=/usr/local/share/hostedx115.rbf

My default VG1 setting is -25 and VGA2 is 5.
That VGA1 setting is really low if you're trying to transmit over the air. Try VGA1=-8, VGA2=10.

Note that you should not need to use fpga= if the image is stored in the autoload path.

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