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[RuudNL]

Recently I had problems with interference on one of my U87ai microphones. After some investigation, this turned out to be caused by a time code transmitter (432 MHz, 10 mW) in the vicinity of the microphone. Because it was unclear whether the interference signal came in via the cable or through the openings in the headbasket, I initially tried to solder additional capacitors directly to the pins of the XLR insert, unfortunately without noticeable results. Surprisingly, an older U87i does not show any sensitivity to HF fields in the immediate vicinity.
Would there be a solution to make the U87ai more resistant to (fairly low) HF fields?
I want to try wrapping the microphone in aluminum foil to see if additional shielding will solve the problem.
(Although that is of course not a workable situation!  )

EDIT: If I wrap the headbasket with aluminum foil, the interference disappears completely. It therefore appears that high-frequency signals enter through the mesh of the headbasket.

[klaus]

Before we reinvent the wheel, can we maybe start checking off some simple things first?

My suggestion:

Get a decent XLR cable - a three-conductor with Reussen layer shield like a Gotham GAC3 would be a good start.
Then terminate shield and ground to XLR pins #1 on BOTH connector ends, and also connect the ground tab that makes connection to the connector housing to pin #1 ON BOTH connectors. Then please report back.

I suggest no funny business with capacitors, etc.: they just robb audio quality (as they already do in the stock U87 setup with the 330pf caps to ground).

[RuudNL]

Gotham GAC3 cable is exactly what I am using.
It is clear that the disturbance doesn't enter the microphone through the cable, but through the mesh of the headbasket.
Because if I wrap the microphone in aluminium foil (as I mentioned), the disturbance caused by the HF signal is completely gone.