Re: Recommendation for high sample rate receiver?

[CEL]

Hi Mike,
thanks for following up on this:
A signal with 0.1 microsecond rise time definitely has definitely more
than 6 MHz bandwidth :) so that's where my confusion stems from.

It will have something upwards of 20 MHz, rule of thumb should be
around 100 MHz bandwidths, and that fits nicely with the bare necessary
40 MHz bandwidth for do anything at a 25ns timescale.
As said, if you can capture that amount of bandwidth, you can infer the
timing – you really do not need 500 MS/s, as far as I can tell from
your description of the signal.
Then again, there might be complicating factors – extreme dynamic
range, for example.

Could you tell us more details about your signal? And also, "as
accurately as possible" is not a spec; could you say "I need a timing
accuracy of X ns, given an SNR of Y dB", so that we could help you
there?

Best regards,
Marcus

On Sat, 2020-02-01 at 02:58 -0500, Mike wrote:
> Thank you to all who commented.
> 
> The target signal of interest uses pulse modulation where each pulse
> is 1 microsecond in duration, with a rise time of less than 0.1
> microsecond and a decay time of less than 0.2 microseconds.  The goal
> is to identify the start (arrival) of a transmission at each receiver
> site as accurately as possible (better than 25 ns).
> 
> Interpolation adds no useful information regarding start time, of
> course.  Lower sampling rates lose arrival time resolution.
> 
> No affordable SDR supports 500 MS/sec; I'm looking at A/D evaluation
> boards with an RF front end.
> 
> 
> Thanks!
> 
> 
> 
> On 1/29/2020 10:34 PM, Kyeong Su Shin wrote:
> > To whom it may concern:
> > 
> > Forgot to mention: There is a Wikipedia article, listing SDR
> > receivers with various capabilities ( 
> > https://en.wikipedia.org/wiki/List_of_software-defined_radios ).
> > There's also something called OneRadio ( 
> > http://www.oneradiocorp.com/ ). I saw an actual build of OneRadio,
> > and it was pretty impressive (but expensive, of course). 
> > 
> > Do not expect these receivers to be well-supported by GNU Radio,
> > however. However (I think it is not necessary, but), if you still
> > want to get a fast receiver and do not want to roll out your own
> > receiver using oscilloscopes or FPGAs, then I guess         these
> > are possible alternatives. 
> > 
> > Regards,
> > Kyeong Su Shin
> > 보낸 사람: Kyeong Su Shin <address@hidden> 대신 Discuss-gnuradio <
> > discuss-gnuradio-bounces+ksshin=address@hidden>
> > 보낸 날짜: 2020년 1월 30일 목요일 오후 12:10
> > 받는 사람: address@hidden <address@hidden>; 
> > address@hidden <address@hidden>
> > 제목: Re: Recommendation for high sample rate receiver?
> >  
> > To whom it may concern:
> > 
> > It is already well-discussed, but I would like to add a few points:
> > 
> > -If you absolutely want to have a such receiver (it's pretty
> > meaningless, as discussed already, but if you still want to), then
> > you can grab a digital oscilloscope or a similar hardware and
> > attach a RF frontend to it. You will end up losing some (actually,
> > most of) samples, but you cannot run non-trivial data processing
> > chains at 500MS/s in real-time with a generic desktop CPU anyway.
> > 
> > -Regarding on why this is pretty meaningless (not using the Nyquist
> > criterion or maths, but using intuitions): consider two consecutive
> > samples, sampled by your receiver. Since the sampling rate is way
> > higher than the bandwidth of the signal, these values are going to
> > be nearly identical. There could be a bit of differences in the
> > amplitude and the phase, but the differences will be pretty small
> > and will be easily washed out by the noise. You cannot expect to
> > get reliable TDOA results           from that. You will have to use
> > more samples to get more reliable results.. or just use a slower
> > receiver, anything that satisfies the Nyquist criterion. 
> > 
> > -If you know the structure of the transmitted signal (like PRNs in
> > GPS), and if you are dealing with CDMA-like signals, then maybe you
> > want to review the GPS receiver design principles and apply that to
> > your design. Not sure if that's the case, though..
> > 
> > -Please consider power difference of arrival or phase
> > interferometry as alternative methods.
> > 
> > Regards,
> > Kyeong Su Shin
> > 보낸 사람: Qasim Chaudhari <address@hidden> 대신 Discuss-
> > gnuradio <discuss-gnuradio-bounces+ksshin=address@hidden>
> > 보낸 날짜: 2020년 1월 30일 목요일 오전 11:05
> > 받는 사람: address@hidden <address@hidden>; 
> > address@hidden <address@hidden>
> > 제목: Re: Recommendation for high sample rate receiver?
> >  
> > Hi
> >    A high sample rate for such ns times of arrival resolution is
> > impractical. Same holds for high SNR and longer times of
> > measurement. GPS and most other high resolution positioning systems
> > stitch the information together from the signal time of arrival
> > with the carrier phase of arrival. Since carrier frequencies are
> > incredibly high, their phase can provide such ns accuracy because
> > the phase information is preserved across the downconversion stages
> > with sufficient linearity. For this purpose, the algorithms also
> > need to determine the integer number of arriving wavelengths.
> > 
> > Cheers,
> > Qasim