Characteristics of HP-IL Transformers?

[J-F Garnier]

(09-06-2020 06:11 PM)J-F Garnier Wrote:  The input path uses two transformers in cascade, this was designed in this way for the ESD protection.

Carefully reading again the HP Journal article on HP-IL (p.15), it turns out that the reason for the two-transformer design of in the input path was more dictated by EMI considerations:
The design of a receiver circuit to handle [externally generated EMI] transients turned out to be a major undertaking. [..]
Because of the difficulties in manufacturing very small transformers with shields, it was found that the two transformer approach is more cost-effective. [..]
The design results have been very rewarding. With the design approach outlined here, prototype systems that failed the susceptibility test at 100V transient amplitudes were able to handle 500V to 1000V transients and did not exhibit any transmission failures below a field strength of 5V/meter.

However, for retro/hobby projects, we don't need such EMI performance, and a single transformer solution is very acceptable.

J-F