Gandalf_Sr
Member level 1
vk3bhr
I've adapted the front end for this frequency counter (see diagram) from a design byPhil Rice VK3BHR and it works well. Now I want to put in some front end protection for the AT-41533-TR1 emitter follower front end transistor, it's rated at a max of 1.5V Vbe and the 74AC161 is good for a max input frequency of 200 MHz. L1 is supposed to help at high frequencies and its value is 10uH. The I/P and I/P Grnd are connections to a 50 Ohm BNC connector. Pin 15 of the 74AC161 feeds into RA4 of a PIC.
If I fed a 5V 100MHz signal into this circuit it would probably blow the transistor.
Can anyone offer any guidance on how to approach adding protection please?
I've adapted the front end for this frequency counter (see diagram) from a design byPhil Rice VK3BHR and it works well. Now I want to put in some front end protection for the AT-41533-TR1 emitter follower front end transistor, it's rated at a max of 1.5V Vbe and the 74AC161 is good for a max input frequency of 200 MHz. L1 is supposed to help at high frequencies and its value is 10uH. The I/P and I/P Grnd are connections to a 50 Ohm BNC connector. Pin 15 of the 74AC161 feeds into RA4 of a PIC.
If I fed a 5V 100MHz signal into this circuit it would probably blow the transistor.
Can anyone offer any guidance on how to approach adding protection please?
