UHF indicator or wavemeter is some kind of device that measures frequencies and determines LC circuit frequecy resonance . This device does not need to radiate.
The oscillator is build with T1 and T2 (2 x BF494) and can be adjusted with C1 and Lx. The Lx coil is connected outsite of the metal box and has to be changeble handiest.
If Lx is inductively coupled with another LC coil wich has the same frequency as the wavemeter, then will extract energy from oscillator coil, this will result in a voltage reduction.
With Lx = 2 turns 1mm (SWG19) over 15mm, the ultra high frequency indicator – wavemeter frequency cover is 50 … 150 MHz.
BF494 transition frequency is 150Mhz, if you want to measure higher frequencies change it with BFR 91 wich has an Ft of 250MHz.
If you want to use this uhf indicator as an absobtion wavemeter or rf field measurement unplug from the battery, in this case you have to look for a minimum value on the multimeter.