13 August, 2011

Small voltmeter for a QRP rig

AT Sprint rig in an Altoids box, itself contained in a video case.
Digital voltmeter in lower left corner shows 12.0 Volts.
(Click for larger image)
Every battery-operated rig needs a voltmeter. I had a small analog voltmeter for my AT Sprint QRP (= low power), 4 Watt rig, but after it failed I wanted to upgrade it to a digital one. I found a miniature meter on Ebay which is perfect for a QRP rig and which I recommend.

The display itself measures only about 22 by 14 mm which is small compared to the Altoids tin of the rig. It works from 3.2 to 30 V and takes its power from the measured voltage so no separate power is required. The current consumption is about 10 mA at 12 Volts. I bought it from seller super.store.usa on Ebay (China).

I have connected it via a header so I can easily turn it off in order to save battery. It also seems to generate a small amount of RFI on certain bands when on, so it is best turned off most of the time except for short checks of the battery. As it is not protected against reverse connection of the supply voltage, it is connected after the reverse protection diode of the radio. This is no disadvantage as it then measures the actual supply voltage of the rig.