Flirting IQ stream

[Maksym]

Hello All.
I have BB60C.
What limit exist for BW flirting for getting IQ stream?
For example when I use:
bbConfigureIQ(int device, int downsampleFactor, double bandwidth)
What minimal correct (for successful flirting) value bandwidth can I use?
Thank you.

[Justin Crooks]

Maksym,
The power of 2 downsample factor sets the theoretical bandwidth that is available. For example, a downsample factor of 4 gives you 10 MSPS, which theoretically represents 10 MHz of bandwidth. But you should leave 20% for filter rolloff, etc. so generally bandwidth will be 40% to 80% of the total bandwidth based on your downsample rate.

[Maksym]

Hello Justin
Thank you for answer.
With “douwsampleFactor” I understood. It is clear from API Manual.
For me interested third parameter from bbConfigureIQ. It is “bandwidth”

bbConfigureIQ(int device, int downsampleFactor, double bandwidth)

I tested receiving IQ stream for GSM. So I think that in BB60C exist digital filter.
Examples:
I can synchronization with GSM signal if I use:
bbConfigureIQ(int device, int downsampleFactor, 200000)
and I cannot do it if I use
bbConfigureIQ(int device, int downsampleFactor, 2000000)
Because I have mixed with others GSM channel.
But if use “bandwidth” = 2000 I can synchronization with GSM signal. So I don’t fill difference between 2000 and 200000.
Probably parameter “bandwidth” has some limit for low value.
Can you give me some description?
Because I cannot find it in API Manual.

[Andrew]

Maksym,

The bandwidth parameter controls the FIR filter cutoff frequency on the IQ data stream. The lower limit for IQ bandwidths are below. Additionally, the final IQ bandwidth is reported back to you in the bbQueryStreamInfo function after you initiate an IQ data stream. Ideally, you should target a bandwidth between 20-80% of the sample rate, because with fixed lengths FIR filters, the filter rolloff duration will be constant. If you need a narrower bandwidth, I would suggest either lowering the sample rate, or running an additional larger filter on the IQ data after you acquire it.

case 1,2: return 50.0e3;
case 4: return 50.0e3;
case 8: return 50.0e3;
case 16: return 50.0e3;
case 32: return 50.0e3;
case 64: return 50.0e3;
case 128: return 50.0e3;
case 256: return 20.0e3;
case 512: return 10.0e3;
case 1024: return 5.0e3;
case 2048: return 2.0e3;
case 4096: return 1.0e3;
case 8192: return 0.1e3;

[Maksym]

Andrew. Thank you.

[Maksym]

Hello.
I fact I have issue (problem) with douwsampleFactor. I use PPS for synchronization two IQ stream from BB60C. So I have trigger with accuracy (time) of samples. So if I will use filter on BB60C (for filtering 10kHz) I will have slow sample (douwsampleFactor = 512) and incorrect time (time with low accuracy). Then I need develop filter on my source code.
Can I outflank that issue?

[Andrew]

Hello Maksym,

You are correct in noting the BB60C triggering accuracy is only provided at the output sample rate. This means if you need higher trigger precision you would need to stream at a higher sample rate and then filter/downsample after retrieving the I/Q samples. I apologize for the inconvenience.

Regards,
Andrew

[Author]

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