[hpsdr] Toroid evaluation for filters, transformers, IIP3

[Phil Harman]

> ...
> I find it quite amazing that on 40M toroids with a size usually used
> in 100W PEP transmitter output LPF's are required to remove the IP3
> bottleneck in the receiver.
> ..."
>

Hi Glenn,

We found the same issues when designing the HPFs for the Alex project,
hence the reason for using such large toroids.

BTW, it is really hard to measure IMD at > 40dBm, I had to build my own
test equipment to do this since I could not find any commercial equipment
that would measure at this level.

I also found that a really big core (T200-2) would also introduce IMD. OK,
it was at the noise floor but it was still visible!

73's Phil...VK6APH


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