[Elecraft] Improved sidetone

[Bob Nielsen]

Can you provide a URL for the "baudline" software?  Possibly this would
be an alternative to using Spectrogram (my wife wouldn't appreciate
dragging her Windows computer into the shack).  I looked at the Hamsoft
site (http://radio.linux.org.au) and couldn't find any reference to
baudline there.

Thanks & 73,

Bob N7XY

On Mon, Nov 18, 2002 at 10:18:39AM +0000, Marteinn Sverrisson wrote:
> 
> Improved Sidetone in K2...
> 
> I have not been satisfied with the sound of the current
> side-tone in my K2. I have done the side-tone mod, using a 47mH choke.
> 
> Looking at the circuit it is a High-Pass filter with some 
> peaking in the 600Hz region but it does not attenuate the
> higher order harmonics of the side-tone.
> 
> Why not make a Low-Pass filter using the same choke?
> I moved the 47mH choke (rs=180 Ohm) in series with 
> C33 (the 2.2uF cap) and put a new 2.2uF cap across Rp5 pins 7 and 10, 
> making a genuine LP filter. 
> The internal resistance rs of the choke controls the Q of the filter.
> This makes a huge improvement of the side-tone sound, now it is soft 
> and sweet :-).
> 
> To make the mod I had to cut the trace from C33 leading to U10,
> I cut it next to C33 and inserted the choke across the gap, 
> soldered it to the C33 pad and the pad for C35, 
> this is done on the underside of the Control Board. Then solder
> a small 2.2uF cap between pins 7 and 10 on Rp5.
> 
> Here are measurements of the side-tone harmonics before and after.
> The harsh sidetone is now gone and instead a softer tone is now 
> generated, almost a pure sinewave.
> 
> Side-tone at F0=600Hz, reference level 0dB.
> 
>                 Before          After
> 
> 600Hz           F0=0dB          F0=0db
> 1200Hz          F1=-16dB        F1=-42dB
> 1800Hz          F2=-27dB        F2=-42dB
> 2400Hz          F3=-54dB        F3=-70dB
> 3000Hz          F4=-47dB        F4=-70dB
> 
> Higher order harmonics not visible on the spectrum, with the new LP filter.
> Measurements done with "baudline" program running on Linux.
> 
> 73's
> TF3MA
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-- 
Bob Nielsen, N7XY                          n7xy@n7xy.net
Bainbridge Island, WA  
IOTA NA-065, USI WA-028S