[K2] Diode types for connecting both paddle & straight key

[Steve Kavanagh]

I'm replacing a dead diode in my paddle/key combiner box.  Does it matter at all what types of diodes I use ?  I am thinking maybe I should use something less prone to RF pickup (say 1N4001 or similar) rather than the HP 5082-2835's (small signal schottkys) I had there originally.
 
73,
Steve VE3SMA
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[Sverre Holm (LA3ZA)]

It is an advantage to use a Shottky diode for the auto-detect circuit and not a standard silicon diode.

I've given the arguments for that here: Reliable auto-detect for keyer for Elecraft K2

[Mike K8CN]

Steve,
Virtually any diodes should work in this setting.  If you have volts of RF on your straight key/paddle/computer keying lines, the change to a conventional silicon diode with its slightly higher offset voltage won't give you any freedom from false triggering.  Are you experiencing RF feedback issues with your existing setup?

I've used 1N4148 diodes in my K2/10 computer keying line without problem for several years, but that's only because I had an abundance of them in my parts bin.

73,
Mike, K8CN

[Steve Kavanagh]

Thanks for your comments, Sverre and Mike.  Yes, I believe I have had RF-induced odd keying problems (with a transverter/amp on 144 MHz at about 100-300 W out, the key being around 5m from the antenna, but not in the main beam).  They seemed to respond to moving cables around, putting ferrite chokes on cables and the like, but it was never very certain what was happening.
 
I have a whole bunch of TCG125 general purpose rectifiers (1 kV, 2.5 A) so I tried a pair of them last night.  They seem to work, though the only real test will be extended operating time.  I measured the voltage on each of the dash and dot paddles with the straight key down (0.53 and 0.42 volts) and the total current through the straight key (0.7 mA).  With half this current through each of the 220 ohm filter resistors I should have 0.61 and 0.50 V at the PIC, so this would appear to be adequate according to the criterion suggested in Sverre's link.
 
I hope it works ok...if not I do have a few 1N5818 Schottky rectifiers which haven't made into projects yet....
 
73,
Steve VE3SMA
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