Sunday, 2018-07-01

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emeb_macawygle: Interesting - tbh I haven't paid much attn to the power requirements of the various ADCs I've used. Mostly interested in high rates & resolution and that always has a cost.00:50
awygleemeb_mac: sure! whereas my applications are almost all narrowband and power-constrained00:51
awygledifferent constraints, different design (despite all the SDR hype ;)00:51
emeb_macawygle: for really narrowband stuff it might make more sense to go with more analog in the front end.00:51
awygleemeb_mac: yes, that's what i've historically done. but it would be nice to be able to play more interesting protocol games00:52
emeb_macmy HFRX radio has very similar back-end processing as iceradio, but uses a QSD to convert RF to I/Q analog, then uses a high-res 50kSPS ADC00:53
emeb_macmight be a better fit for what you want00:53
emeb_macof course a QSD has some of its own problems, but those are solveable...00:54
awygleoh that is interesting. i've never tried a QSD before00:54
tpbTitle: HFRX (at
emeb_macawygle: you probably have seen the circuit used - just not always called that.00:55
awyglei had put together a similar design (in the sense of using a high-end STM) but with a more conventional downconversion stage, but i couldn't get it to hit all three of performance/power/price targets00:55
emeb_macyeah - designing radios is a vast multi-dimensional space to optimize00:57
awygleyup yup00:57
awyglesadly i'm mostly out of this game now but i'll definitely do more reading on this approach00:58
emeb_macthat STM32F373 is a fun part - it's got some really nice 16-bit differential ADCs that are surprisingly low noise.00:58
emeb_macworked pretty well for doing the DSP on the back end of that quadrature ZIF front-end.00:58
awygleit appears from my notes i was looking at the F30300:58
emeb_macVery similar part, but w/o the good ADCs00:59
awyglei think i might have been aiming for higher sampling rate and paying less attention to performance01:00
awyglebut it was a long while back01:00
emeb_macIf power is an issue then iceRadio was definitely not optimized for that.01:01
emeb_macespecially with the R820T2 VHF front end - that thing gets pretty toasty.01:01
awyglethe interesting aspect of that design from a power perspective is that the ice40up potentially represents a very low-power way to do the baseband processing01:03
awyglealthough it's sort of unclear to me how it would compare to something like an STM01:03
awygle(i'll freely admit i am better at the frontend than the digital stuff)01:04
emeb_macWell, the FPGA is fairly low-power, but I use it to do the wideband downconversion all digitally. An STM32 doesn't have the horsepower to handle 40MSPS data in any way.01:05
emeb_macThat high sample rate means it's able handle most of the HF band in one gulp, but it immediately reduces it down to a ~40kHz bandwidth, so some might argue there's more efficient ways to do that.01:08
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awygleideally i would like to take in something like a 500k-2Mbps QPSK signal and put demodulated bits or even higher-level packets out over something like I2S. perhaps including FEC in the fpga as well01:10
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awygleah well. someday. too many irons in the fire already to work on something like that now.01:11
emeb_macThat's probably doable in a UP01:12
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ZipCPUWoohoo!  All six butterfly forms are now working.  That means the whole FFT works as well!  Yaaaaayyyy ...02:54
ZipCPUMust mean its time for bed.02:54
ZipCPUSigh.  Celebrating too soon.  I had the first three multiplies working, and ... they aren't anymore.  I'll have to check the git history on Monday.  *SO* close.02:56
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