On 2/20/14, 8:51 PM, Bob Camp wrote: > Hi > > You can get parts in the 18 bit and up range for not a whole lot of money > with rational sample rates for a WWVB receiver. Analog Devices and Linear > Tech both make some interesting looking parts. They get you into the >=100 db > dynamic range area.
Yes. 192ksps is considered audio and is now available as a common part for consumer devices. Or go with a 1-bit part and then decimate the hell out of the result. > Even with a lower bit count part, you pick up some bits in the downsampling > process. As long as you have enough noise to keep things moving, you can > track pretty far down into the crud. GPS receivers do that sort of thing all > the time. > > Since this is slow audio after the CIC decimator, things like ARM chips > probably have enough DSP horsepower to do what you need to do. The decimator > it’s self is not terribly taxing if you don’t go too crazy with the rate > change. This all makes more sense to me than hacking a bunch of op amps and filter hardware. Use a low bit-depth but fast part then decimate. If it is fast enough you can get by with very simple anti-alias filtering. Like you said, if you have enough noise to randomize the LSB you are good to go. I bet that the AMBCB provides more than enough randomization power. And if it doesn't, just inject enough broadband noise to randomize the LSB. The rest is just SMOP. Just for giggles I took a look at the output of the ADC on my Hermes board. The input is my Pixelsat loop which is broadband from 50kHz to 30MHz. (It has significant output down to below 20kHz.) The ADC of my Hermes HPSDR board is being fed with the raw output of the antenna with no filtering so the ADC is seeing everything from DC to 60MHz that comes out of the antenna. Peak ADC level at my location is -40dBFS. I live about 35km N of San Antonio so my location is neither particularly RF quiet nor noisy. Seems like the 16-bit ADC has plenty of headroom. I hear WWVB very handily on this setup and I am seeing -83dBm out of my antenna for WWVB on peaks. (Actually the S:N is pretty good at over 16dB in a 300Hz bandwidth.) This is near noon local time. -- Brian Lloyd, WB6RQN/J79BPL 706 Flightline Drive Spring Branch, TX 78070 br...@lloyd.com +1.916.877.5067 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.