'RF bias' microphones can provide an effective alternative to the use of conventional high impedance condenser microphones in situations where moisture can be a concern (outdoors - high humidity environments, etc).
Their design uses much lower impedance circuitry for capsule control, and that can help alleviate noise problems which may occur when using conventional condenser microphones in outdoor locations.
More details on the concept: HERE
Currently, it is believed that only Sennheiser and Rode utilise this concept commercially - and the microphones using this approach tend to be expensive devices.
Until now there seems to have been very little use of the concept in the DIY hobby world of microphone building, with inductor details seemingly a stumbling block to the design of any hobby mics.
This project is an attempt to correct that by presenting a simple DIY RF biased condenser microphone - using 'off the shelf' inductors...
The idea offers one solution to the request at the start of THIS THREAD on the 'Group DIY' forum
My thanks to all those who have contributed to the 300+ posts now in that thread - to Gerard, the thread starter - to Ruud for his prototype PCB layout - to Ricardo and Abbey for their expert suggestions - and especially to Khron for his expertise and patience in designing the various versions of the final project PCB layout. All helped to drive the project forward - again, my thanks.
To see the details of the various parts of the project, just click on any of the buttons above - or below!