[Towertalk] Back-To-Back Diodes - Careful!!

Pete Smith n4zr@contesting.com
Wed, 04 Dec 2002 13:11:14 -0500


At 09:37 AM 12/4/02 -0800, Ward Silver wrote:
>Danger, Will Robinson!  The back-to-back diodes are terrific harmonic 
>generators and mixers.  If you have strong local BC stations, you will 
>cause yourself a lot of grief as these little guys generate their mixing 
>products.  Also, if you're in a multi-transmitter environment, the local 
>interference they generate will also cause a lot of trouble.  If you have 
>neither of these to worry about - no sweat - but remember they are there.

Hi Ward -- I'm having a little trouble converging two pieces of conflicting 
advice.  When I asked about receiver protectors, most folks recommended 
back to back diodes or strings thereof across the receiver input, as well 
as a series resistance or lightbulb.

You're concerned about harmonic generation.  Am I right to assume that 
harmonic generation only occurs if the voltage applied to back-to-back 
diodes exceeds their forward voltage drop?  Could you avoid this problem, 
then, by stringing enough diodes together so that they limit at a higher 
voltage, but one still safely below the rated maximum for the receiver?