Cutoff frequency for RF rejection?

[Fusion916]

What -3db frequency do you guys use to suppress RF? 100MHz? Even lower?

 

[Bone]

50kHz

 

[rayma]

What -3db frequency do you guys use to suppress RF? 100MHz? Even lower?

As much as the frequency, it matters also how the suppression is executed in the particular hardware.

 

[RJM1]

Just my opinion, but I go about 300Khz to stay away from the 100KW AM transmitters ( 540 to 1700Khz). I had a problem in the 1970's with a CB radio (27Mhz) over comming my HK Citation I's phono preamp section only rated at 80Khz.

 

[AndrewT]

F-3dB between 100kHz and 300kHz, passive at the input.
I use ~700us for my passive RC.

 

[mcd99]

I use around 300kHz. 2nd order filter.

 

[AndrewT]

Might be worth mentioning that these "filters" attenuate the RF. They don't remove, nor eliminate it.
A filter eventually stops filtering at some highish frequency.
Two filters staggered by a couple of decades, may perform better than one "super filter".

 

[AndrewT]

I use around 300kHz. 2nd order filter.

How do you implement your 2nd order filter?

What Q does it achieve?
Does it have any "ringing" as a result of 2pole characteristic?

I use a 47oF at the input socket and then my ~700us RC at the PCB.
Strictly this is a staggered frequency 2pole, or maybe a 3pole if cable inductance has a significant effect.
I don't know how to analyse it for Q, nor ringing.

 

[DF96]

A filter eventually stops filtering at some highish frequency.
Two filters staggered by a couple of decades, may perform better than one "super filter".

Yes. Don't expect a filter to work from 50kHz to 2.4GHz.

 

[wg_ski]

Just my opinion, but I go about 300Khz to stay away from the 100KW AM transmitters ( 540 to 1700Khz). I had a problem in the 1970's with a CB radio (27Mhz) over comming my HK Citation I's phono preamp section only rated at 80Khz.

If you get enough MHz or whatever signal coming in, it can overload a stage and force it into nonlinearity. Then you hear the modulation signal. This could even happen in a power supply component (and your electrolytics are no good at these frequencies). The RF level required to do this may not even be very high as you don't have much if any distortion-reducing feedback at RF.