[Elecraft] Vibroplex Bug

[Steve Ellington]

All you need is a 1uf capacitor across the bug contacts. Radio Shack has 
some that are small enough to fit in an RCA plug! Actually .5 UF is enough 
so I have 2 ea. 1UF in series. These eliminate the mushy and double dit 
symptom. Cleaning doesn't always work. Some modern rigs such as the K3 and 
Omni 7 are overly sensitive to switch noise and the cap will clear it up.
Radio Shack PN is:  272-1434
Steve
N4LQ
N4LQ at carolina.rr.com
----- Original Message ----- 
From: "Vic K2VCO" <vic at rakefet.com>
To: "'Elecraft List'" <Elecraft at mailman.qth.net>
Sent: Sunday, August 23, 2009 3:19 PM
Subject: Re: [Elecraft] Vibroplex Bug


> 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
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