Re: [Discuss-gnuradio] tx_time tag accuraccy

[bob wole]

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

On Mon, Jun 9, 2014 at 10:05 AM, Tom Tsou <address@hidden> wrote:

On Wed, Jun 4, 2014 at 2:01 PM, bob wole <address@hidden> 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