[Elecraft] K2: Erratic action of the Hand Key "Autodetect" function

[Tom Hammond]

If Sverre's solution to the problem (Schottky diodes) is the answer, then 
the 1N5711 should work nicely... and they are pretty easy to find... even 
if you order them from Elecraft.

73,

Tom   N0SS

At 02:14 PM 5/9/05, Sverre Holm wrote:
>-----Original Message-----
>My K2 (and I've talked with several other K2 owners with the same problem),
>Serial #4338, will not always detect a hand key properly -- Autodetect is
>turned on in the menu - and I am using 2 1N914 diodes between the hand key
>contacts and the dot and dash inputs to the K2.  The keypaddles function
>properly at all times, but when using the hand key, at random times, a key
>down on the hand key produces the same results as a paddle press - namely
>automatic dots or dashes.
>----
>
>I have resolved a similar problem some time ago that hopefully may shed some
>light on your problem also. The symptom appeared similar, seemingly random
>keying.
>
>The series diodes in the autodetect circuit will make the K2 input no longer
>0, but say 0.7 Volts (for Si diodes) when keyed. When I tried to key the K2
>using autodetect and the diodes from my PC via an optocoupler I got into
>trouble. The saturation voltage of the optocoupler was not small enough and
>when added to the 0.7 Volts, the total was not low enough for the K2 to
>reliably sense a key-down.
>
>The optocoupler (4N31) had a voltage of 0.65 to 1.8 V in saturation. I
>lowered it by increasing the drive current in the LED, but still had almost
>1.4 V (opto 0.65 + Si diode 0.7). The remedy was to replace the autodetect
>diodes with Shottky diodes. I have several hundreds of PRLL5818 in my shack
>so I used one of them, but the type is not critical at all. The data says Vf
>< 0.33 V at I = 100 mA, so the forward voltage with the low current here is
>even smaller than that.
>
>73
>
>Sverre
>LA3ZA
>http://www.qsl.net/la3za/
>
>
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