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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.

[klaus]

Hello Ruud, I am curious: did you follow my cable termination recommendation? Yes? No?

If you did, the mic's housing would be included in the grounding of the mic's housing facilitated by the terminations I recommended. The faraday cage, then, would be complete, as the triple mesh of a U87 basket is dense enough to fully shield the high-impedance section of the head.

[RuudNL]

It is obvious that the disturbance enters the microphone through the mesh of the headbasket.
The microphone body is properly grounded. (Ground resistance is close to 0 ohms.)
If I cover only the headbasket with aluminium foil, this eliminates the disturbance completely.
It seems the only way to get rid of the disturbance is to reduce the emitted power (only 10 mW) of the timecode transmitter.
And yes, I checked the cable connection; the shield is both connected to pin 1 and the connector shell.

[gtoledo3]

One point about the discussion up to now.

If there isn’t proper ground, interference can still appear to “enter” through the headbasket even if there is no real issue with the headbasket.

[RuudNL]

In that case the interference would enter the microphone through the body too, but it doesn't.
If I only cover the headbasket with aluminium foil, the disturbance is completely gone.
(Today I ordered a 10 dB attenuator to be placed between the timecode transmtter and the antenna. I hope this will solve the probem.)

[klaus]

And yes, I checked the cable connection; the shield is both connected to pin 1 and the connector shell.

Are you sure on BOTH connectors?

[klaus]

If I only cover the headbasket with aluminium foil, the disturbance is completely gone.
(Today I ordered a 10 dB attenuator to be placed between the timecode transmtter and the antenna. I hope this will solve the probem.)

U87 are virtually RF proof-they were specifically designed for RF-rich broadcast environments.
I would therefore try to first isolate a possible defect in the shield/ground coverage of the mic before moving outward.

Your eliminating the noise via basket shielding gives me pause: touch basket and XLR pin #1 of the mic with an ohm meter: zero ohms?