Hi Alex, List, On Sun, Jan 23, 2011 at 3:03 AM, Alexandru Csete <oz9...@gmail.com> wrote: > On Sun, Jan 23, 2011 at 2:56 AM, Arya Santini <arya.santi...@gmail.com> wrote: >> Hi GNURadio, >> >> I'm new to the USRP and trying to understand the number of RF >> input/output channels available (USRP1). From the GNURadio wiki >> (http://gnuradio.org/redmine/wiki/gnuradio/UsrpFAQIntroMobo), I gather >> we have 4 possible TX and RX channels each, since we have 4 ADC's and >> 4 DAC's on the motherboard: > > Hi Arya, > > Thanks for reading the doc - it makes explaining easier :-) > >> >> "..in principle, we have 4 input and 4 output channels if we use real >> sampling. However, we can have more flexibility (and bandwidth) if we >> use complex (IQ) sampling. Then we have to pair them up, so we get 2 >> complex inputs and 2 complex outputs." >> >> This means we could have only 2 complex TX/RX channels. >> >> Also from the USRP FAQ page >> (http://gnuradio.org/redmine/wiki/gnuradio/UsrpFAQIntroFPGA), in >> explaining the DDC implementation, it is said: >> >> "Note that when there are multiple channels (up to 4), the channels >> are interleaved. For example, with 4 channels, the sequence sent over >> the USB would be I0 Q0 I1 Q1 I2 Q2 I3 Q3 I0 Q0 I1 Q1, …etc. In >> multiple RX channels (1,2, or 4) , all input channels must be the same >> data rate (i.e. same decimation ratio)." >> >> Do these multiple RX channels (1,2 or 4) refer to those coming out of >> the ADC's? Then contrary to the aforementioned, how come now there are >> 4 complex channels, I0,Q0 - I3,Q3 coming in. when it should be >> possible to have only 2 complex RX channels? Looks like I'm >> understanding the architecture incorrectly! > > This multiplexing refers to the data stream on the USB interface, i.e. > after FPGA processing where the real signal is converted to > quadrature/complex signal. So the 4 RX channels that use real samples > are converted to complex signal in the FPGA. >
Okay, there are a total of 4 pairs of IQ signals, each of the 4 real outputs from the ADCs being converted to an IQ pair in the FPGA. >> >> Some help here would be greatly appreciated. >> >> Also, on the daughterboard, each RX port has access to 2 ADC's. So in >> the context of having 2 RX channels possible per daughterboard (in the >> case of Real sampling, and total 4 for the system) are the inputs >> RX_A_A, and RX_A_B separate/independent? I mean, does the RF >> daughterboard circuitry receive two frequencies simultaneously on a >> single receive antenna? > > I am not entirely sure about this so someone may correct me if I'm wrong... > The LFRX and BasicRX are not quadrature receivers so the use real > sampling and conversion to quadrature signal is done in the FPGA. You > can however also chose to input quadrature signal in which case you > use RX_A_A and RX_A_B as I and Q input. This works in the two receiver > configuration. Suppose we're dealing with real signals alone, then we have 4 input channels viz. RX_A_A, RX_A_B, RX_B_A, RX_B_B. My question is, are each of these channels independent of each other in the sense that their frequencies are different i.e are they 4 different RF signals? In other words, on each daughterboard, can the circuitry be configured to receive on 2 separate frequencies from the same antenna, and feed them as inputs to each of the 2 ADCs its RX port is connected to? > If you use the 4 receiver configuration then 2 > additional receivers have to be mounted on the TX_A and TX_B slots. > Therefore, if we chose to use 4 receivers we can not have transmitters > at the same time. > > Alex > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > Thanks, Arya _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
