[Elecraft] Vibroplex Bug

[Vic K2VCO]

Ron D'Eau Claire wrote:
> I suspect you're experiencing "scratchy" or intermittent dits, not chirp.
> ("Chirp" is when your frequency shifts up or down during the initial
> milliseconds after the key closes) 
> 
> As others pointed out, a good low resistance contact is *required* by modern
> rigs that key a low voltage/low current line, which is a problem with
> mechanical contacts, especially contacts that just "bump" with little
> pressure like the dit contacts on a bug. 

Deoxit helps, as Ron says. Also intermittent cleaning with a business card. But the real 
solution for bug keying of modern rigs -- even the K3, which *is* better than the K2 at 
this -- is a simple circuit composed of a reed relay with a capacitor across the coil to 
soak up the contact bounce.

Here is a description and schematic. You will need to use a fixed-width font to see it 
properly:

Get a radio shack 12 volt SPST reed relay (275-233) or similar. One side of the relay coil 
goes to the positive terminal of a 9v battery and the other side goes to your bug's 
ungrounded contacts.  In parallel with the coil put a 4.7 to 10uf 25v electrolytic 
capacitor (also from Radio Shack) and any silicon diode.  Orient the capactitor so that 
the positive side goes to the coil terminal that is connected to the battery.  The diode 
is reverse-connected; its CATHODE goes to the coil terminal that is connected to the 
battery.  Finally, connect the negative side of the battery to the bug's grounded side. 
If you want to run the circuit from a 12v supply instead of a battery, put an 820 ohm 1/4w 
resistor in series with the 12v.

                           coil
           |------------+@@@@@@@+--------> to bug
           |            |       |
           - +          +--| (--+ 4.7 to 10 uf capacitor
          --- - 9v      |       |
           |            +--|<---+ diode
           |------------------------------>
          ///

Here's a photo of such a circuit attached to a bug:
<http://www.qsl.net/k2vco/Bug640.jpg>

The value of the capacitor should be the smallest necessary clean up the bounce. The large 
it is, the more it will stretch the dots and you will have to adjust the dwell time of the 
dot contact on your bug to compensate.

Yes, I have tried various electronic debouncing circuits, and none of them proved as 
satisfactory to me as this simple one. The relay is almost silent (the slight tick is 
drowned out by the noise of the bug).
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco