improvised faraday cage

[Highlander]

It will depend on the strength of the impulse, so a difficult question to answer fully,... certainly what you describe is already a Faraday cage, but adding more protection is better

Take the hand held radios we both carry with us to work,.. we have them a cardboard box, and wrapped in foil, the type that goes behind radiators,... but we then put that box in a 10 inch metal money box.

Its carried [ with a few other things ] in a small rucksack