HackRF sends 8bit samples, same as the RTL dongle. 20Msps * 8bits * 2 (complex sampling) = 320Mbit/s, or 67% utilization. The Ettus B100 gets 10.6Msps on most USB host controllers, sometimes 12.8Msps if you have a really nice USB host controller with nothing else on the bus -- 71-85% utilization with 16bit samples. You can double that if you select 8 bit sampling mode for the B100, for 21.3-25.6Msps, at the cost of dynamic range. The RTL dongle appears not to be able to continuously sample above 2.4Msps for reasons that are unclear to me, but certainly not due to a USB2.0 limitation.
--n
On Sat, Sep 21, 2013 at 2:37 PM, Leif Asbrink leif@sm5bsz.com wrote:
Hi Adam,
The bandwidth of the I/Q pair is too large to be transmitted over USB for the reception of TV signals. After demodulation the bandwidth is lower so it would (marginally) fit an USB interface if we talk about traditional analogue TV. For digital TV the bandwidth reduction by the decoder is much larger.
Is that correct? From what I can find, an analogue TV signal has a bandwidth of around 6-8MHz.
Yes.
The HackRF is an SDR that works over USB2.0 and can capture a chunk of RF spectrum up to 20MHz, which should be ample for one analogue (or even digital) TV signal, perhaps even two if the channels are close enough together.
I was under the impression that the USB channel was the reason that the highest sampling rate I was aware of in continous mode is 4 MHz (QS1R) Now, I did not think of the fact that for the dongle we need only 8 bit while normal SDRs use 16 bit so with my assumption the maximum sampling speed would be 8 MHz. To receive 6-8 MHz bandwidth one would need to sample quite a bit higher. Surely one could apply digital filters but even so a, substantial amount of oversampling is needed.
Are you sure HackRF really can send 20 MHz of bandwidth over USB 2.0 continously? Where did you find that info? (Seems I should try to push SDR manufacturers who use USB 2.0 to supply modes with higher sampling rates...)
73
Leif