Yes a Faraday cage blocks both directions. What walrus is saying I think is that if you are a good citizen, you should do any radiating GPS jammer testing insid

Yes a Faraday cage blocks both directions. What walrus is saying I think is that if you are a good citizen, you should do any radiating GPS jammer testing inside a Faraday cage. Doing it outside a cage is probably illegal and could create a public safety hazard (911 on cell phones for example). You could have a test setup bringing GPS inside the cage with coax+circulator or radiate a GPS constellation simulator inside to test the jammer.