Based on the help in this thread my new FM transmitter set up worked perfectly to transmit 30 feet through one wall from my mixer to an audio receiver.
This is the transmitter I used.
https://www.amazon.ca/gp/product/B01K4NI9RS/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

I connected the mixer directly to the transmitter from the "control room" outlet.
Finding an unused frequency was no problem, perhaps I am lucky in my location.
Using a AC/DC adapter to power the transmitter worked perfectly.
I did get quite a bit of static initially but managed to eliminate this by repositioning wires. I also discovered that the transmitter needed to be positioned so that there is no human body close to the transmitter inline with the receiver, including my own.

Tony