I have time-synchronized RTLSDRs using a known, pseudo-random, sequence
injected into the RX inputs using directional couplers. These all had
a common clock so they wouldn't drift apart.
On 2017-08-16 11:57, Derek Kozel wrote:
> It should be pointed out that the hardware based timestamping is only needed
> if you need time alignment better than a half second or so. With USB
> transfers, various buffers, NTP based alignment of the host computer's time,
> and some extra code on the host side you could do a coarse time alignment,
> probably with less than a half second of error.
>
> You could also time align the streams if both radios receive the same signal
> and you know the distance (and other details depending on the precision
> needed) between the transmitter and your two receivers. This is done by many
> protocols like the cellular standards to create a distributed timebase, but
> quickly becomes non-trivial.
>
> The B200 does timestamping in the FPGA and can use a 1PPS signal to align to
> GPS time. It is more expensive than the HackRF, but much less than the $3000
> mentioned above.
>
> On Wed, Aug 16, 2017 at 4:20 PM, Sylvain Munaut <246...@gmail.com> wrote:
>
>> On Wed, Aug 16, 2017 at 5:11 PM, <b.shube...@sirinsoftware.com> wrote:
>>> What type of hardware? I thought from hardware point of view only precise
>>> clock is required and all the other things in
>>> firmware. I've naively thought i could modify hackrf firmware to get this
>>> feature.
>>
>> Mostly a FPGA and a PPS input from a GPS receiver.
>>
>> Each individual sample has a timestamp of when it has been received.
>> And you can also reset the timestamp on the next PPS edge.
>>
>> Technically it would be possible to modify the hackrf firmware and
>> repurpose some GPIOs and have all samples transmitted to the host be
>> in timestamped packets and implements timestamping in the on-board
>> ARM.
>> For additional hardware you'd only need an external GPS receiver (or
>> some other way to have both a single freq reference + single sync
>> pulse).
>>
>> Cheers,
>>
>> Sylvain
>>
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