Measuring from 20Hz up to say many MHz with any digital multimeter

At your risk. DMM are nice small, consume little energy but most ofter fail to measure above 3KHz. So here is what to do, the idea and schematic came from a vilntage transistor Philips micrvoltmeter able to measure up to many hundreds of MHz with its simple RF probe. The probe converts AC to DC. What can we use to do this up to a very high frequency? A Germanium diode! Here is the description of the schematic. Signal to be measured passes through a small high voltage capacitor. Then a Germanium diode is connected shunt to ground. Then on top a series resistor of 100Kohms buffers and its other side is connected to the high impedance DC voltage meter! So frequency responce tests can be done easily and lightweightly.