[Elecraft] FSK Issue

[Joe Subich, W4TV]

These symptoms are classic common mode RFI issues.  Typically 
due to unbalanced RF on the shield of the coax coming back 
from the antenna.  SWR has nothing at all to do with common 
mode - swr is measured in differential mode on the inside of 
the transmission line.   

See K9YC's information on common mode RFI at: 
  http://www.audiosystemsgroup.com/RFI-Ham.pdf 

The first thing to do is properly ground the shied of the 
coax (and the shield of the control cable) of the SteppIR 
vertical where they enter your shack and then install 
common mode chokes between the "ground window" and the 
rest of the station.  After that, install a choke of 6 to 
8 turns on a #31 mix toroid in the FSK line between your 
computer interface and the Aux/Acc input of the K3. 

In all probability the shield of the your coax is acting like 
another radial on 80 meters.  I'd almost bet is it very close 
to an odd multiple of 65 feet (as the coax runs) from the 
antenna to the rig. 

73, 

   ... Joe, W4TV 
 
 


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Dave Reed
> Sent: Saturday, April 04, 2009 11:25 PM
> To: Elecraft at mailman.qth.net
> Subject: [Elecraft] FSK Issue
> 
> 
> I seem to have this recurring problem with FSK on my K3.  Up
> until now, the problem was intermittent, often solved by 
> rebooting my computer and/or reloading MMTTY.  Well, without 
> changing anything, the problem has now become consistent, 
> persistent and predictable:
> 
>  
> 
> At 0 - 22W on 80m, or any power level on 6m - 40m, MMTTY (using my
> interface) will key the K3 and send normal RTTY tones using
> the FSK-D data mode.
> 
>  
> 
> At 23W and above, on 80m, MMTTY will key the K3, but I only
> get the high tone.
> 
>  
> 
> Of course, if I put the radio into test mode, I get normal RTTY tones.
> 
>  
> 
> Am I overlooking something obvious?  Going crazy?  SWR
> presented to the K3 is 1:1 (SteppIR BigIR vertical).
> 
>  
> 
> AFSK works fine using the AFSK-A data mode, but I don't want
> to use AFSK.
> :-)
> 
>  
> 
> 73,
> 
> Dave, NX7F
> 
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html