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Here's an adapter that turns a digital voltmeter (DVM) into a field strength meter (see Figure 1). The DVM is well suited to the purpose because it's sensitive (down to 1 mV) and can detect slight changes in signal level (e.g., 0.1-percent change at 1 volt).
Fig. 1
I built the adapter in a plastic film can. Banana plugs are epoxied into holes in the can so that the device plugs directly into the DVM. In operation the meter is set to the 2-volt DC range. The antenna is a short wire whip.
Parts aren't critical. The capacitor (0.1 µF) is larger than usually used. Unlike a conventional meter, the DVM has no inherent damping action; if its input has an AC component, it refuses to settle on a definite reading. The larger value capacitor reduces this problem.
N4TMI, Michael A. Covington.