At 11:41 AM 4/24/2008, you wrote: >Please correct me if I am wrong, but it appears to me that QSK on a >SDR encounters a wall at the receive latency interval, which sets a >minimum bound for recovery of reception. > >After the completion of transmitting a code element, the receiver is >going to be receiving the tail of that element for the duration of >the receive latency period. After that, the AGC has to recover.
The AGC (being in software) could recover instantly (i.e. be at the level it was before you started transmitting) (I haven't looked at the code recently, but I think it does this.. that is, the AGC loop is held fixed during Tx time) >Even in split or with a second receiver what will be heard between >elements happened the latency interval earlier in time. only if the monitor isn't also passed through the Rx. If you put the Tx sidetone through the Rx, it will have exactly the same latency as the received signals. You'll hear both your signal and the other guys, properly aligned. >Current SDR latencies are running in the range of 100ms or more. This >latency will have to be reduced by at least a factor of 10 before >there can be a 10ms recovery in QSK. All receivers, including totally analog ones, have some time delay through them. To a first order, one could approximate it as (1/IF bandwidth) * # of filter sections. For a 200 Hz filter with 3 or 4 sections, that's already 20 milliseconds. Then, there's the 3-5 milliseconds delay in the air from speaker to ear (unless you're on headphones..) Admittedly, 100ms is pretty long, but I don't know that PowerSDR is that long, especially with small buffers and fast sample rates. >The low level of latency required for true QSK is achieved in box- >based SDR units like TenTec and FT-2000. Why is it not being achieved >in computer-based SDR's like the Flex 5k? > >My two cents... _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
