VINTAGE COMMTRON SWR Power METER for VHF/UHF Ham Radio #8040 | eBay
File:SWR-Meter.jpg - Wikimedia Commons
Second Hand Monacor FSI-40 FSI-40 SWR Power 1.5-150MHz Meter
Would anybody know what the knob in the middle of this meter does? I was given one like this by a friend but not sure how to operate it. Thanks for the