Regarding ofdm blocks in gnuradio-3.7

hi community,

i tried using the examples provided in gr-digital/examples/ofdm. when i
use
them i couldn’t able to get the peaks at the output of Schmidl&cox block
but if i change the tx_ofdm.grc in such a way that only payload then i
can
able to detect the peaks. i tried using the logging from ofdm_pn block
and
plotted in Matlab. which gave me the peaks. what could be the problem
when
i use both the header and payload at the transmitter at a time. looking
forward for reply.

thanks,
lingeswar