Regarding two pages of Artex B406 ELT Manual I have just emailed, would you explain thoroughly what is the principle of the performance test and? What is the Attenuator? What is measured by the measuring device? Why operational Test should be done within the first 5 minutes of the hour?
Attenuation is the reduction in signal strength. Usually a load resistor is used for this purpose.
During test, you don't want the signal being broadcast out if possible. The 121.50 signal is just a warble tone. The 406 is a data burst with all the aircraft information. This includes the registration number and lat/long position if the IRU's are up.
Doing the test at the top of the hour is a standard for just about everyone using ELT's. Emergency services realize a non-continuous signal 5 minutes before to 5 minutes after the top of the hour is just a test.
Using a tester as above (direct hook-up) prevents all external transmission.