Clock oscillator on KerberosSDR?

Discuss KerberosSDR - 4x Coherent RTL-SDR
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Chris Eilbeck
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Joined: Tue Apr 16, 2019 12:21 pm

Clock oscillator on KerberosSDR?

Post by Chris Eilbeck » Tue Apr 16, 2019 12:29 pm

Is there a schematic and/or parts list available for the KSDR? I'm particularly interested in the clock oscillator and working out whether it's good enough as is or can be upgraded to allow me to do some GPS capture synchronously at L1 and L2 frequencies.

I'm yet to take mine to bits ...

rtlsdrblog
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Re: Clock oscillator on KerberosSDR?

Post by rtlsdrblog » Wed Apr 17, 2019 2:18 am

We don't have a schematic sorry the hardware isn't open source.

The TCXO is 1PPM or better, so that should be good enough for GPS decoding. Same TCXO as used in the V3.

Chris Eilbeck
Posts: 2
Joined: Tue Apr 16, 2019 12:21 pm

Re: Clock oscillator on KerberosSDR?

Post by Chris Eilbeck » Wed Apr 17, 2019 10:36 pm

Thanks for getting back to me. I'll post my results when I've managed to do something with it. Now to make some antennas ...

jsalsburg
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Joined: Wed May 15, 2019 9:56 pm

Re: Clock oscillator on KerberosSDR?

Post by jsalsburg » Wed May 15, 2019 11:06 pm

Synchronizing clocks for SDRs is a well established technology, first used to sync data streams for Radio and RADAR Astronomy in the late 1970s. To forgo the boring details of how this is done with SDRs, I will say that it is a technique using a sudo-phased-locked-loop. The SDR's clock frequency varies according to the one second heartbeat of the GPS System. A ring counter, typically 10 MHz or higher, is set up or down depending on where the beginning of the ring count falls compared to the GPS Heartbeat. If the Ring count is too high then the number of ticks in the ring are added slowing the clock; too low, ticks are subtracted, speeding the clock. Plus there are environmental restrictions like Oven stabilization of the clock circuits, etc. It may not be practical to try this with an existing design, the Clock must be generated externally unless the radios are initially designed with this feature. It does not end there; the individual data packets must contain the Time-code and location code for each sample with high enough resolution to coordinate packets from multiple receiver/antenna locations perhaps separated by thousands of miles typical of RADIO Astronomy observations. For Passive RADAR, this task is daunting and becomes statistical nightmare requiring each physical site to be highly tweaked, with petabytes per day of data possibly generated.
http://radar.salsburg.com/
https://www.orolia.com/resources/knowle ... ronization

Docdailey
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Joined: Tue Jun 18, 2019 10:45 am

Re: Clock oscillator on KerberosSDR?

Post by Docdailey » Tue Jun 18, 2019 10:48 am

Would the creators of this unit be interested in adding a 10MHz ref in? I Ordered one and would love to connect it to fury gpsdo for increased precision.

Doc

rtlsdrblog
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Re: Clock oscillator on KerberosSDR?

Post by rtlsdrblog » Fri Jun 21, 2019 5:27 am

It's possible, but as 28.8 MHz is required it would require additional circuitry which would add cost...

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