My 5 cents I agree with Helmut's analysis. Additionally, with such a low IIP3, the radio will be absolutely riddled with intermods and essentially unusable in a city.
NE602 is good for a cordless telephone, or a well protected 2nd IF mixer function. By modern standards they are a low performer. The radio is certainly fine in the lab as a demonstration aid. aim for an IIP3 of > -10dBm for a cheap radio. For this design, I'd suggest an IQ sampling because it can be done effectively by the STM32 ADCs. IQ sampling, will in general be a lower power consumption solution as it doesnt have high speed ADCs and high speed downsampling filtering (fpga) . There will need to be considerable gain between the ADC and the antenna. Say sample rate 256kHz, SNR 60dB, say full scale of 0dBm, Noise floor = -60 -54 = -114dBm (Hz)... a noise figure of around 60 dB.... Likely needs to be a double conversion receiver- so this would maybe be portioned as 12dB pre mixer gain, active mixer IIP maybe +6dBm, low noise post mixer , IF filter say easy available 21.4 filters, some more gain, and then use a CMOS switch SDR style IQ mixer with some more low noise opamps before feeding your STM32 ADCs. Keep the noise floor in the 1st half as low as possible, enabling you to really heap on the gain in the baseband opamps .... as heaping on the gain at the baseband wont risk a feedback/instability issue. of course, you could use a CMX994 and a couple of opamps and feed your STM32 dual ADC. I have some CMX994s on order. g On 25/02/2015 12:46 PM, David Rowe wrote > Hello, > > To support VHF FreeDV developments I've been working on a really simple > and very open SDR architecture for VHF radio: > > http://www.rowetel.com/blog/?p=3884 > > Glen and Matt - would appreciate you suggestions on appropriate input > BPF filtering and a VHF mixer. Also pls let me know if you see any show > stoppers in this architecture. > > Cheers, > > David > > ------------------------------------------------------------------------------ > Dive into the World of Parallel Programming The Go Parallel Website, sponsored > by Intel and developed in partnership with Slashdot Media, is your hub for all > things parallel software development, from weekly thought leadership blogs to > news, videos, case studies, tutorials and more. Take a look and join the > conversation now. http://goparallel.sourcefor ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
