[TangerineSDR] Setting up DE for selected bands and sample rate
tom.n5eg at gmail.com
Sat Apr 18 15:23:49 EDT 2020
Hi Nathaniel -
Responding to question 1: the requirements for the DE putting out 8
channels sampled at 10 Hertz are similar to 8 channels
sampled at higher rates. The very low sample rate requires the FPGA low
pass filters have many more taps, but I think
that's small-ish compared to other FPGA things.
Responding to #2 (from the original post) The algorithm in the paper would
probably be implemented in the Local Host as software.
I'm not sure it would be easy nor useful to figure out how to compute that
in FPGA as opposed to in CPU. But at 10 Hz sample rate,
that computation is likely feasible in CPU. There will be the initial
collection of samples to get the estimator started, then it can update
frequently (i.e. 1 second rate).
I can't comment on question 3.
-- Tom, N5EG
On Sat, Apr 18, 2020 at 3:37 AM Dr. Nathaniel A. Frissell Ph.D. <
nathaniel.frissell at scranton.edu> wrote:
> Hi Bill and Tom,
> 1. If we run the DE in the 8 channel mode for doing these measurements, do
> we think that will max out the data engine to prevent it from doing
> anything else?
> 3a. I agree that we probably do not want to emulate a sound card. I would
> like to see a program like FLDigi be able to accepts files or buffers. It
> would be good not only for the PSWS, but al also for doing post-processing
> of data in general.
> 3b. We need the ability to collect both the raw spectrum and the derived
> frequency estimate. Exactly how to interpret and use these things is still
> an active area of research. Steve WA5FRF is actively working on this and is
> probably the best person to work with on this right now.
> Maybe David Kazdan can comment to address Tom’s question on needing 100
> seconds of measurements.
> 73 de Nathaniel W2NAF
> Dr. Nathaniel A. Frissell, Ph.D., W2NAF
> HamSCI Lead
> Assistant Professor
> Department of Physics and Electrical Engineering
> University of Scranton
> (973) 787-4506
> On Apr 17, 2020, at 1:41 PM, Tom McDermott via TangerineSDR <
> tangerinesdr at lists.tapr.org> wrote:
> Hi Bill - thanks for the link to the paper. I don't have access to the
> references in the paper, particularly
> , , , and , so I am missing the details of the critical first
> step. My reading of the paper indicates that
> the initial estimate of the frequency is needed, and that initial estimate
> has to distinguish between adjacent
> spectral bins, those being +/-fs/N apart. (Section 2.1, step 1.)
> So perhaps I'm reading this wrong, but it still seems like one needs 1000
> samples to separate
> out the desired bin, assuming 10 Hz sample rate and 10 milliHz resolution,
> that is 100 seconds.
> [ The DFT doesn't need a power-of-two sample size, it can just be a
> convenient number. ]
> -- Tom, N5EG
> On Fri, Apr 17, 2020 at 8:52 AM Engelke, Bill via TangerineSDR <
> tangerinesdr at lists.tapr.org> wrote:
>> In yesterday’s HamSCI research telco
>> we discussed several ideas on how to accomplish several goals with the
>> TangerineSDR; a summary is below for your review and comment.
>> 1. We currently think that the Data Engine (DE) will have the
>> capacity to simultaneously collect up to 8 channels of data for observing
>> Doppler shift in carrier frequencies, i.e., WWV at 2.5, 5, 10, 15, 20 MHz
>> plus CHU at 3.33, 7.335 and 14.670 MHz. We think we can do this by
>> observing excursions of up to +/- 1 Hz from the carrier frequency with a *precision
>> of 0.01 Hz, with measurements taken every second *(see next point).
>> 2. In earlier discussions on this board, it has been stated that this
>> kind of precision (10 milliHz) would require a 102.4 second sample time;
>> this assumes the processing is linear. CWRU is using a non-linear method in
>> the low-cost approach to extract a frequency estimate, which uses fldigi to
>> achieve the 10 milliHz resolution once per second, and it was discussed
>> that TangerineSDR could be set up to do this as well. (Reference here:
>> 3. I won’t try to explain the method mentioned above, as it is at the
>> very limits of my understanding; however, a couple of observations…
>> 1. The CWRU low-cost system uses fldigi to implement the frequency
>> estimator, and in looking at fldigi I see that it requires sound card
>> input. In the case of the TangerineSDR, we will have buffers of IQ data. I
>> don’t think I want to use some sort of kludge to take the buffers and
>> somehow emulate a sound card (do I?) – another option might be to implement
>> the frequency estimator algorithm in the Small Board Computer (SBC) of the
>> TangerineSDR. If we could/should do this, I would ask for a volunteer to
>> code it; I fear that if I try to do it, it would take far too long for me
>> to get up the learning curve. The code (C++) for the algorithm as used in
>> fldigi is online (included with hundreds of other routines; see
>> http://www.w1hkj.com/files/fldigi/ ). A third option might be to
>> persuade the fldigi team to support buffer or file input.
>> 2. As I understand, the frequency estimator outputs a single
>> value: the strongest signal in the band. A downside of this is that there
>> seems to be a lot of other possible information in the data (Steve Cerwin
>> has shown data he has collected showing Doppler effects but with multiple
>> structures including various modes in both time and frequency domain). We
>> need some guidance from the science community: what data do we really need
>> to do the desired science?? Maybe we need to implement/support both raw
>> data collection & frequency estimation at the same time(?)
>> 3. In yesterday’s call, we discussed that we should be able to
>> specify an 8 ksps sample rate and a center frequency, and get the desired
>> 10 milliHz resolution – frankly, I am still fuzzy on the details of this,
>> so I wish someone (David Kazdan? Kristina?) would chime in and explain, for
>> the record, how this works.
>> 4. Channel configuration settings for the DE:
>> 1. The DE will be able to tell the SBC what data rates it
>> supports. We are working with 2-byte command codes; in general, a command
>> ending in “?” is a query, i.e., send the DE the command “S?” and it answers
>> “AK” , a simple health check. Send the DE the command “R?” – it will
>> respond with a table such as the following:
>> 1 2000 2 4000 3 8000 4 16000 etc. – where
>> each entry is 2 integers: an index and a sample rate (Hz). To put a channel
>> into data rate of 8000 sps, we put 3 into the channel setting.
>> Please comment! -73- Bill, AB4EJ
>> TangerineSDR mailing list
>> TangerineSDR at lists.tapr.org
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