Where is the Preamble settings?

[nbl]

I want to change the preamble to short on my router (XT8 running Gnutron's Merlin build) but I cannot find the setting under Professional or anywhere else. What am I missing?

 

[Tech9]

It's 2.4GHz only setting.

 

[octopus]

I want to change the preamble to short on my router (XT8 running Gnutron's Merlin build) but I cannot find the setting under Professional or anywhere else. What am I missing?

Look under Wireless - Professional => Preamble type