I am amateur radio operator and I have a SWR/Power Meter that works in the VHF/UHF range. It has no backlighting for use in low light. I was thinking about using an LED for the backlighting. I dont want to use manual switch or battery power if possible. The manual switch is a definate NO for this, battery power is ok if need be. I was thinking using some sort of diode to pick off some of the RF rectify it and then use that to power the led or switch transistor to power the led.

Doable right???

 

Hello,

On a VSWR meter there are two outputs.
One for the forward power and one for the reflected power.
http://web.telia.com/~u85920178/use/vswr-00.htm
When you compare the output with a reference value , you can decide to turn on the led or not.

Greetings,
Bertus