[Elecraft] Final Update To Keying Mod Change

Tue Apr 20 02:18:01 2004

Bill;
Its not a completely simple choice.  If you use a 270K or 220K resistor, the
falling waveform takes up more bandwidth (because of the glitch near the
bottom of the falling waveform).  If you use the 180K, the rising waveform
takes up more bandwidth.  I opted for the 180K resistor in my K2 since that
gave me nearly equal rise and fall times and reduced amplitudes at offset
frequencies greater than 500 Hz.

You can always find a slower edge rate that will occupy less bandwidth.  If
we double the risetime and falltime, we will halve the occupied bandwidth.
Its just a matter of picking a reasonable point that produces a reasonable
bandwidth occupancy.  This is where the decision gets somewhat subjective.
-John
 KI6WX

----- Original Message ----- 
From: "Bill Tippett" <[email protected]>
To: <[email protected]>
Sent: Monday, April 19, 2004 2:11 PM
Subject: Re: [Elecraft] Final Update To Keying Mod Change

> KI6WX wrote:
>  >I've posted a final update to the 180K resistor value
> change for the Elecraft Keying Modification.
>
> Hi John,
>
>          I just installed a KAF2, thanks to W4YN, as a solution
> to my filter blow-by problem mentioned previously.  Blow-by is
> now gone with either AF1 or AF2 (I chose your "Low Ringing"
> mod), but it's still there with AF Off, i.e. the passive LPF does
> not take care of blow-by products <3 kHz.  BTW, #4119 uses
> your crystal grounding technique (less SMT caps) but mine
> still has blow-by.
>
>          While I had my Control Board out, I changed R21 to
> 180k as you suggested.  After doing this <ggg>, I decided
> to  completely read your webpage documentation plus
> previous posts about key clicks.  I noticed there was some
> debate about whether to opt for minimizing <500 Hz products
> (Elecraft's mod) or >500 Hz products (your mod).
>
>          I believe you made the right choice for the following
> reason.  If I'm <500 Hz from a very strong station, I know
> I'm asking for many serious problems (phase noise, IMD,
> BDR, etc. in addition to key clicks).  Key clicks <500 Hz
> are probably a second-order effect compared to the other
> problems I'll have with strong signals.  On the other hand,
> it's not unusual to have strong stations spaced at 500 Hz
> and up in contests, so I want to minimize clicks >500 Hz for
> these situations, assuming I'm a "good citizen" and not
> intentionally maximizing my bandwidth to keep others
> away (some EU stations are notorious for this in contests).
>
>          Thank you for the many valuable contributions you
> have made to improving the K2 for all of us!
>
>                                  73,  Bill  W4ZV
>
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