Forum: GNU Radio Re: tx_time tag accuraccy

4eff8471dd77455a25564f9df9b2bd2e?d=identicon&s=25 bob wole (Guest)
on 2014-06-04 20:47
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Marcus! Thanks for you comment.

I think that USRP transmit FIFO is at the start of the DSP chain in FPGA
i.e it is prior to both of the interpolation filters? right?  I am not
talking about when the burst will be over the air, I want to know when
the
first sample of the burst will leave the transmit FIFO if it has been
tagged as tx_time=X.



--
Bob
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus Leech (Guest)
on 2014-06-04 21:09
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4eff8471dd77455a25564f9df9b2bd2e?d=identicon&s=25 bob wole (Guest)
on 2014-06-05 08:03
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Sorry for not stating the hardware earlier. I am using USRP N210, with
RFX2400 and WBX boards.

--
Bob
Ddb503356cb90b0c95e52700445ef749?d=identicon&s=25 Tom Tsou (Guest)
on 2014-06-09 07:07
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On Wed, Jun 4, 2014 at 2:01 PM, bob wole <bnwole@gmail.com> wrote:
> I think that USRP transmit FIFO is at the start of the DSP chain in FPGA i.e
> it is prior to both of the interpolation filters? right?  I am not talking
> about when the burst will be over the air, I want to know when the first
> sample of the burst will leave the transmit FIFO if it has been tagged as
> tx_time=X.

If you tag a burst with time X, that burst will be released from the
device buffer at time X - assuming the burst arrives at the device
before time X. After time X, there will be a sample rate dependent
delay and a fixed analog group delay before the burst can be observed
at the antenna output.

In other words, a burst tagged to transmit at time X will leave the
buffer at time X.

  -TT
4eff8471dd77455a25564f9df9b2bd2e?d=identicon&s=25 bob wole (Guest)
on 2014-06-09 08:16
(Received via mailing list)
Hi Tom,

Thanks for your comment. I do not think if I tag a burst with time X,
it'll
go out of USRP transmit FIFO at exactly X, there would be  some small
delta
involved depending on the clock resolution, and I want to know that
delta.
I know that there would be some DSP delays, depending on sample rate,
and
analog delays *AFTER* the burst leave transmit buffer.

--
Bob
Ddb503356cb90b0c95e52700445ef749?d=identicon&s=25 Tom Tsou (Guest)
on 2014-06-09 16:23
(Received via mailing list)
On Mon, Jun 9, 2014 at 2:15 AM, bob wole <bnwole@gmail.com> wrote:
> Thanks for your comment. I do not think if I tag a burst with time X, it'll
> go out of USRP transmit FIFO at exactly X, there would be  some small delta
> involved depending on the clock resolution, and I want to know that delta. I
> know that there would be some DSP delays, depending on sample rate, and
> analog delays *AFTER* the burst leave transmit buffer.

The N210 clocking rate is 100 MHz, which gives timing resolution of
10ns.

  -TT
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