[TangerineSDR] Setting up DE for selected bands and sample rate
m0ycm at veenstras.com
Fri Apr 17 15:08:20 EDT 2020
You might consider looking at what the FAROS software (NCDXA) does with time
of arrival measurements on the HF beacons. Good representation of effective
ionosphere heights (time of arrival measurements) and thus Doppler
estimation as the path changes. The beacons waveforms ate synced via GPS.
The WWV/CHU waveforms offer the same time of arrival possabilities.
Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y
<mailto:lester at veenstras.com> lester at veenstras.com
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From: TangerineSDR [mailto:tangerinesdr-bounces at lists.tapr.org] On Behalf Of
Engelke, Bill via TangerineSDR
Sent: Friday, April 17, 2020 11:52 AM
To: TAPR TangerineSDR Modular Software Defined Radio
Cc: Engelke, Bill
Subject: [TangerineSDR] Setting up DE for selected bands and sample rate
rhtaid=286> 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:
&type=pdf> &rep=rep1&type=pdf )
3. I wont try to explain the method mentioned above, as it is at the
very limits of my understanding; however, a couple of observations
a. 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 dont
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.
b. 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(?)
c. In yesterdays 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:
a. 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
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