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Downconverter protection



I'll be using a TH-F6A HT with an AIDC downconverter to receive AO-40 and
want to protect the AIDC and/or a Drake.  It has been suggested that an 
AIDC's output is hot enough that it may only require an attenuator for 
protection if there isn't much feedline.  Is that other folk's experience, 
or would it be wiser to use a pre-amp and alot more attenuation?

More to the point, would the following circuit power and protect an AIDC,
and give good performance?  I've included values for 6dB attenuation, but 
i plan to use a step-attenuator to find a more optimal value.

                To AIDC
              *  ("F")  o
              |         |              2.5V
              |         |              | |
              +---UUU---|---* ... *---||||-----o
              |   RFC   |              | |
              |         |  15V                13.8V
             ---        |
             --- C1     +---o ... o------------o
              |         |
              <         |
              < R1      |
              <         |
              |    R2   |
              +--vvvvv--+
              |         |       75ohm 6dB:
              +---|>|---+       R1 = R3 = 25 ohm
              |   D1    |       R2 = 100 ohm  
              +---|<|---+
              |   D2    |       
              *		|	F1 = smallest fuse available
	     (  F1      |
              )		|
              *		|
              |         |
              <         |
              < R3      |
              <         |
              |         |
              *  To HT  o
                 (BNC)


Is that enough to keep 5W safely away from the downconverter?  How about 
50W?  Do the back-to-back diodes help?  Would ordinary diodes (1N400x)
provide enough protection at 146/440 MHz or do i need something faster?  

Will 6dB attenuation really provide enough protection or am i better off 
including a pre-amp?  Is there a better approach?

			         -- KD6PAG
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