[Elecraft] 1N5711 diodes in directional coupler

[Lyle Johnson]

Hello Fred! 

> Gary says that 1N5711's give more accurate readings than 
> lessor diodes such as the 1N4148... question; how much more 
> accurate, and how critical is this accuracy?  Would the 
> 1N4148 be more, less, or the same susceptability to ESD?

The 1N5711 is a Shottky barrier diode; the 1N4148 a normal silicon diode.
The improved accuracy is gained by substantially reduced forward voltage
drop, about 0.2 to 0.3V for the 1N5711 vs. about 0.6 to 0.7V for the 1N4148.
The result of substituting (and after "calibration") would be to make low
power readings too low, which in practice means overly optimistic SWR
readings.

> I don't have any 1n5711's in my stock, but I do have some 
> very fine PIN diodes, labeled, MA 47 266.  Are these 
> acceptable substitutes for 1N5711's?  Would they be more or 
> less accurate in the directional coupler?  Would they be more 
> or less susceptable to ESD damage?

A PIN diode won't work in a directional coupler.  For a coupler you need
rectification of RF, the very feature that a PIN diode is designed to not
possess.

72,

Lyle KK7P