EMRFD Message Archive 13190

Message Date From Subject
13190 2016-09-29 23:48:24 zl1ujg IMD in ceramic capacitors

I have been reading the PA3AKE material wrt the BPF filters used in the receiver.

He states to stay away from NP0 C0G capacitors, as some early tests with different filter configurations gave lower IMD.

I have some PA3AKE type BPF filters built up (using NP0 chip capacitors and just tested the 20m one to the limit of my equipment (currently) and it indicates around +40 dBm.IIP3 (Input Intercept point) which is most probably an equipment limitation. (Running Signalhound SA44)

Has anyone experimented with the PA3AKE filters or have read anything about IMD in NP0/C0G capacitors



13191 2016-09-30 10:34:39 Graham / KE9H Re: IMD in ceramic capacitors
As far as I know the NPO/C0G capacitors are OK, as long as you operate them within Voltage limits.

Other caps, High-K dielectric caps materials like X7R, X7S, X5R will get you into trouble because they are essentially Voltage variable capacitors, and therefore non-linear.

The powdered iron cores (or ferrite) inductor cores can/will generate non-linearities at about the levels you are discussing.

--- Graham / KE9H


13192 2016-10-01 08:52:33 vasilyivanenko Re: IMD in ceramic capacitors
The materials use in each capacitor tempco class varies. Best to test