Shure A15RF In-Line RF Interference Attenuator

[radeng]

A medium length mic line (160') is picking up a local AM radio station between a Shure podium condenser mic and a small Yamaha mixer with the usual opamp from end (no input transformer). Has anyone ever opened up one of these to see the wiring and component values? There are two mic inputs at the same location affected. I already have the XLR M-F bodies to build them into.

 

[Philbo King]

I don't know what's in the Shure mic, but here is a lowpass filter for blocking the AM band (.54 - 1.7 MHz in the USA).
https://www.dxing.com/tnotes/tnote06.pdf

 

[radeng]

Thanks for the link, but that paper is for unbalanced RF transmission lines. The Shure is a balanced mic level filter.