Re: [time-nuts] getting accurate timing on RTL-SDR output

2018-04-14 Thread Magnus Danielson
Hi Jim, > That's the sort of strategy I'm looking at.. find a set of samples where > the transient occurs, zero pad it out (so that when I do peak picking > later, I've effectively got interpolation), then run the correlation You find it using cross-correlation, and once found, you have a fair

Re: [time-nuts] getting accurate timing on RTL-SDR output

2018-04-14 Thread Achim Gratz
jimlux writes: >> A maybe not-so obvious approach would be to use RTL-SDR that have been >> modified for direct sampling (usually via the Q branch) and inject your >> timing pulse there. That would limit the disturbance of the actual >> signal while still relatively easy to extract from the data

[time-nuts] getting accurate timing on RTL-SDR output

2018-04-13 Thread Mark Sims
Note that on a lot of GPS devices that only one edge of the 1PPS pulse is stable and the other edge can jitter a bit. Also, you might want to try programming the PPS to a 50% duty cycle (but having an asymmetrical PPS pulse might have some advantages for post processing). The receiver with the

Re: [time-nuts] getting accurate timing on RTL-SDR output

2018-04-13 Thread jimlux
On 4/13/18 1:47 PM, Magnus Danielson wrote: Hi Jim, On 04/13/2018 06:52 PM, Jim Lux wrote: I'm building a phased array receiver (actually, an interferometer) using RTL-SDR pods, where the elements are isolated from each other - there's a common WiFi network connection, and each node has a

Re: [time-nuts] getting accurate timing on RTL-SDR output

2018-04-13 Thread jimlux
On 4/13/18 1:39 PM, Achim Gratz wrote: Jim Lux writes: So now the challenge is to "line em up". An obvious approach is to transmit an inband pilot tone with some sync pattern, received by all, and I'm working on that too. A maybe not-so obvious approach would be to use RTL-SDR that have been

Re: [time-nuts] getting accurate timing on RTL-SDR output

2018-04-13 Thread Dana Whitlow
Hi Jim, Good for you! I love to hear about backyard radio astronomy projects. With your sample rate your GPS PPS spikes should be in the neighborhood of 1 uS duration. It's hard to say just how accurately you can glean the timing from that, but then I suspect that you're mainly interested in

Re: [time-nuts] getting accurate timing on RTL-SDR output

2018-04-13 Thread Magnus Danielson
Hi Jim, On 04/13/2018 06:52 PM, Jim Lux wrote: > I'm building a phased array receiver (actually, an interferometer) using > RTL-SDR pods, where the elements are isolated from each other - there's > a common WiFi network connection, and each node has a BeagleBone Green, > a uBlox OEM-7M-C, and the

Re: [time-nuts] getting accurate timing on RTL-SDR output

2018-04-13 Thread Achim Gratz
Jim Lux writes: > So now the challenge is to "line em up". An obvious approach is to > transmit an inband pilot tone with some sync pattern, received by all, > and I'm working on that too. A maybe not-so obvious approach would be to use RTL-SDR that have been modified for direct sampling

Re: [time-nuts] getting accurate timing on RTL-SDR output

2018-04-13 Thread jimlux
On 4/13/18 10:33 AM, Dana Whitlow wrote: Jim, I'm curious:In what RF bandwidth will you be recording? 1 MHz for now.. the RTL-SDR isn't a super flexible device - there are apparently good and bad rates - it does a DDC with 28.8 MHz I/Q NCO (with who knows what kind of performance), and

Re: [time-nuts] getting accurate timing on RTL-SDR output

2018-04-13 Thread Dana Whitlow
Jim, I'm curious:In what RF bandwidth will you be recording? My first thought would be to search for a cross-correlation peak between the two antenna outputs, but quickly realized that this does not tell you anything about the timing differences between the two receivers. I think you need