1N5711 diodes in directional coupler

[Indy-3]

These are used in the directional coupler of the K2, KPA, and KAT-100.  I have lost these to ESD more than once.  Several questions;

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?

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?

Thank you!

Please "reply all" as I only get the digest and won't see your reply until tomorrow unless also sent to me directly!!!  If the PIN's are acceptable substitutes would like to install them today.

73,

Fred - kt5x
K2 # 700
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[Lyle Johnson-7]

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


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[Jack Brindle]

I agree with Lyle's discussion on this. The reason for using 1N5711s is
to get low power accuracy. If you are running high power only, then you
probably could get by with 1N4148s in the directional coupler,
sacrificing low power operation.

If you really want to replace them today, you could probably get away
with using the 1N4148s temporarily, replacing them with real 1N5711s
when you get them. 1N5711s are relatively easy to get (here in Silicon
Valley, at least), obtainable from Mouser, DigiKey or even Scott at
Elecraft...

The original Breune bridge circuits favored by many (including DeMaw)
used germanium 1N34 diodes because of their low forward voltage drop.
They are no longer manufactured, and hard to obtain. If you have some
in your junk box, they might be a better selection for temporary (and
maybe longer) use.

On Aug 8, 2004, at 8:14 AM, Indy wrote:

> These are used in the directional coupler of the K2, KPA, and KAT-100.
>  I have lost these to ESD more than once.  Several questions;
>
> 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?
>
> 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?

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