News from the OsmoSDR frontier

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hello everybody, since we found out that the Atmel SAM3U SSC interface is only capable of transporting 500ksps worth of I/Q data, we heard a lot of complaining because of the too narrow bandwith. Especially compared to the rtl-sdr with about 2msps, our 500ksps was bit contrained. The fact, that the OsmoSDR is much more sensitive to very small signals and brings a 14bit ADC instead of 8bits did not really compensate for the bandwidth loss. Also the mismatch between E4000 output resistance and ADC input brought some unwanted spectral effects. Instead of just releasing stuff, we decided to fix both issues: I now have a prototype with simple stack-on-board, that adds two op-amps to decouple the E4000 from the ADC and lower the impedance and also this board connecteds the available FPGA pins to the MCI (SD-Card) interface of the Atmel SAM3U. For this to get working, we had to rewrite major parts of the ARM firmware and the FPGA VHDL code. Today this work is completed and I can report success: The OsmoSDR now delivers up to 4msps at 14bits. Also the strange peaks around Niquist/zero frequency are gone. Find a screenshot of SDRangelove recording a DAB signal at 2msps (SDRangelove needs some more love until it can cope with 4msps in realtime - but we have verified that 4msps works without dropped samples using the builtin FPGA test mode). http://www.cdaniel.de/download/osmosdr-dab-2mhz.png We will now integrate the changes into the OsmoSDR mainboard and reroute the now free SSC pins to the pin headers instead of the MCI interface. Also we will add the opamps. For the already produced OsmoSDR boards, we will have more of the prototype stack-on-top-boards. We will keep you in the loop! Best regards, Christian PS: Regarding the DAB screenshot: - - The horizontal lines are correct - DAB uses a so called "pilot symbol", which only has energy on a few carriers. That's why it looks like a pause in the signal. - - The vertical line is also correct - DAB does not use the middle carrier to avoid I/Q offset problems on the transmitter side. - -- - --------------------------------------------------- | maintech # Dipl. Inf (FH) Christian Daniel | | GmbH ### Otto-Hahn-Str. 15 · D-97204 Höchberg | - --------------------------------------------------- | AG Würzburg, HRB 8790 Tax-ID DE242279645 | - --------------------------------------------------- | http://www.maintech.de cd(a)maintech.de | - ---------------------------------------------------