[Elecraft] K3 AFSK RTTY overdrive - no ALC

[Joe Subich, W4TV]

Chad, 

Start by unplugging the RS-232 (CAT connector).  It us likely that 
the ticking is the computer polling the radio.  You will find that 
is due to ground loop ("pin 1") problems.  

Read K9YC's stuff again very carefully ... connect a jumper from 
pin 5 of the RS-232 connector to the shell (to bypass a choke 
in the RS-232 return) and consider putting a jumper across L4 
(the rear panel "mic" return) on the KIO3 AF board. 

You would also be better served to remove the 20 dB pad and 
connect your soundcard interface to the Line input.  The K3 
will select inputs independently for data modes.  By increasing 
the audio drive for digital modes (and reducing the gain of the 
K3 input) you make it much less sensitive to the RS-232 "spike." 

Remember, RS-232 is a +/- 10V (or more) signal.  If even a small 
amount of that signal flows through the "ground" lead of your mic 
input (normally < 10 millivolts) you will have a serious "pin 1 
problem."  

73, 

   ... Joe, W4TV 
 

> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Chad WE9V
> Sent: Sunday, November 23, 2008 6:08 PM
> To: Jim Brown; elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 AFSK RTTY overdrive - no ALC
> 
> 
> Jim,
> 
> Thanks.  I've seen and read your document previously.  Is 
> there something specific you are referring me to in your 
> document that I already haven't covered?  Let me recap and 
> add a couple points of clarification:
> 
> * It's not an RF problem, as it still exists in TX TEST mode.
> * I do not have a hum/buzz problem.
> * I've used this setup on microphone inputs of other radios, 
> no problem. (FT-920,990,1000)
> * I am using audio transformers.  "Expensive" solution, but 
> it's worked in the past.
> * I am using a ~20dB pad between the soundcard output and iso 
> transformer. (5600/560ohm)
> * Duplicate 20dB pad/iso xfmr are on both channels, other 
> channel driving FT-1000 no problems.  Swapping L/R channels 
> has problem follow K3, not cable.
> * I have 1.25" braid bonding K3>computer>FT-1000.
> * I can turn the soundcard output down very low (<20%), but I 
> have to turn up the K3 MIC to get any power output.
> * Using my Heil headset directly into the K3, I use a MIC 
> setting of 15 on SSB to get 5-6 bars ALC with 0 CMP.  Using 
> this same MIC=15 setting, I adjust my soundcard output so 
> that both the Volume Control and Wave control are both 50%.  
> At this setting, I have no ALC and <50W output power (with 
> PWR set to 100).  I can increase MIC to about 21, where I'll 
> have nearly 100W output, but only 2 bars ALC.  If I back of 
> MIC only one step, to 20, I'll be one bar less than 100W, and 
> only one bar ALC.  If I increase MIC to 23, I get 3-4 bars 
> ALC and the ticking noise.  This seems very sensitive, and a 
> difficult tradeoff between getting 100W output and having the 
> ticking sound (which I'm guessing is some sort of 
> clipping/distortion).
> 
> Others have mentioned being able to use 5 bars ALC with AFSK 
> RTTY.  I can't get anything close to that.  I'd like to 
> reduce the MIC/ALC/output power tradeoff sensitivity.  I've 
> typically left the MIC gain alone on my rigs, and when 
> running AFSK RTTY, I would adjust the soundcard output to get 
> full ALC reading with no compression.  It seems that I can't 
> do that with my K3, only getting 2 bars ALC, and there's a 
> fine line (about 2-3 'clicks" on the MIC gain) between full 
> output power and ticking/distortion.
> 
> So I ask again, is there some specific idea you'd like me to 
> try that I haven't covered?
> 
> Chad WE9V
>  
> 
> 
> On Sun, Nov 23, 2008 at 3:19 PM, Jim Brown 
> <jim at audiosystemsgroup.com> wrote:
> 
> On Sun, 23 Nov 2008 11:37:17 -0600, Chad WE9V wrote:
> 
> >Any ideas out there?
> 
> Lots.
> 
> http://audiosystemsgroup.com/HamInterfacing.pdf
> 
> 73,
> 
> Jim K9YC
> 
>