FSK Issue

[Dave - NX7F]

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

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[Joe Subich, W4TV-4]

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: [hidden email]
> [mailto:[hidden email]] On Behalf Of Dave Reed
> Sent: Saturday, April 04, 2009 11:25 PM
> To: [hidden email]
> 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:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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