[Discuss-gnuradio] ISM band signal recording problem

[WeiXiaowei]

Hi,

I am trying to use GNU radio with daughterboard RFX2400 to record a few period of signal with Bandwidth 20MHz and centered at 2.4GHz ISM band.

Here is the command I use to record signal

Python usrp_rx_cfile.py �Cf 2400M �Cs �Cno-hb -8 data.dat

 

I have a few options, but unfortunately neither of them works.

 

Option 1. use decimation, so the command will be

Python usrp_rx_cfile.py �Cf 2400M �Cd 4 �Cs �Cno-hb -8 data.dat

 

The default decimation is 16 and can be chosen from the range of [4, 256].

My test result are as follows:

If Decimation = 64

USB sample frequency is 1MHz à no uOuO error message

If Decimation = 32

USB sample frequency is 2MHz à uOuO error message appears about 5-10 seconds of recording.

If Decimation = 16

USB sample frequency is 4MHz à uOuO error message appears about 2-4 seconds of recording.

 

I found that the lower decimation rate I choose, the ealier the error message appears.

 

Question 1: If I choose a relatively low decimation rate, say 4. Is it possible to record the accurate signal before the uOuO error message appears? Because 1-2 seconds of the signal is sufficient for me.

 

I have tested the USB speed with the program “usrp_benchmark_usb.py”, it shows it works properly at 32MB/sec. Therefore, theoretically, the USB speed is 256Mbit/sec.

 

Question 2: If I choose Decimation = 32, USB sample frequency = 2MHz and 8 bit per sample (8 bit for I channel and 8 bit for Q channel), the data rate will be (8 bit + 8bit) * 2MHz = 32 Mbit/sec, which is much lower than the USB limit 256 Mbit/sec. But the data overflow message uOuO still appears, why?

 

Option 2. If I do not want to use decimation, but choose to drop some bits before recording, is it possible? Which files do I need to modify and how to modify?

For example, if I choose 8 bit for I channel and 8 bit for Q channel. In order to reduce the data rate to avoid the data overflow, I would like to record the 4 most significant bits and drop the rest, as I believe 4 bits is accurate enough for this signal. Is it possible with minor changes in the code?

Thanks.

Alessandro

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