Mark

I've used one of these before.....

elttesters.com/gadss-tester-gt-1.html

  
     
  
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.