[Elecraft] K3 with SignalLink - Distorted audio in SSB

[Don Wilhelm]

I have to agree with Joe, and I want to amplify on that subject.
I often hear of hams solving similar problems with clamp-on ferrites 
mounted in various places.  That does not solve the basic problem of RF 
floating around in the shack, and once you have fixed one problem with 
the ferrites, another situation crops up giving different symptoms and 
affecting another function of the station.
The real cure is to fix it in the antenna system.  That usually means a 
good common mode choke at the feedpoint of each antenna, and if the 
feedline does not run away at right angles from the radiator for at 
least 1/4 wavelength, the energy from the radiator may be coupled back 
onto the outside of the feedline despite having a common mode choke at 
the antenna feedpoint.  In that case, a 2nd common mode choke outside 
the entry point to the shack will be necessary (on each feedline).

Good and effective common mode chokes are difficult to buy commercially, 
but take a look at the RFI information by Jim Brown K9YC  
http://audiosystemsgroup.com/RFI-Ham.pdf to see how you can easily 
construct effective chokes by winding your coax through a stack of 
FT240-31 ferrite toroid cores.

Note: contrary to common "wisdom" (the shield is 'grounded'), vertical 
antennas often need this treatment more than balanced horizontal antennas.

73,
Don W3FPR

On 3/15/2014 5:14 PM, Joe Subich, W4TV wrote:
>
>> The fact that you are having audio problems with the audio and PTT
>> cables connected to the K3 but disconnected at the far end does
>> suggest that the audio cables may be acting as antennas and picking
>> up RF.
>
> Or acting like a counterpoise to place a RF node on the K3.  In either
> case your symptoms are classic for common mode RF on the outside of
> the feedline.  Spend some time learning about proper antenna balance
> and eliminating the common mode issue rather than chase ways to hide
> it.
>
> 73,
>
>    ... Joe, W4TV
>
>
> On 3/15/2014 4:03 PM, Richard Ferch wrote:
>> What is your MAIN:MIC+LIN set to? It sounds as if it may be set to ON,
>> so that you are getting audio input from both the microphone and the
>> Line In jack. In your setup, MAIN:MIC+LIN should be OFF. When the radio
>> is in Data mode (DATA A or AFSK A), MAIN:MIC SEL should be set to LINE
>> IN to select the SignaLink input and mute the microphone input. In Data
>> modes, the MIC control on the K3's front panel changes its function to
>> act as a Line In level control. Changing MAIN:MIC SEL in Data mode will
>> not change its setting in SSB, and the Line In level setting of the MIC
>> control will not affect the Mic gain setting for SSB. In SSB, MAIN:MIC
>> SEL will still select the correct microphone input and mute the Line In
>> input provided MAIN:MIC+LIN is set to OFF.
>>
>> The fact that you are having audio problems with the audio and PTT
>> cables connected to the K3 but disconnected at the far end does suggest
>> that the audio cables may be acting as antennas and picking up RF. If
>> so, this could continue to affect your signals in DATA modes even after
>> you solve your issues in SSB, and you will need to solve that. There are
>> others who are better qualified than I am to deal with that kind of
>> issue, but one possibility is that you may have common-mode RF on your
>> feedline that is being picked up by the audio or PTT cables.
>>
>> 73,
>> Rich VE3KI
>>
>>
>> K6VWE wrote:
>>
>>> I am using a SignalLink USB interface to my K3 with the cables
>>> provided by
>>> Tigertronics, and the FLDIGI software.  The cables from the SignalLink
>>> are
>>> plugged into line in, line out and PTT on the back of the K3. Things
>>> seem
>>> to work fine in digital modes, although I have actually only tried the
>>> combination on PSK31.  When I switch to SSB, however, I am getting
>>> reports
>>> of distorted audio, and when I monitor my audio I can hear it too.  One
>>> contact said it sounded like the opposite sideband not being suppressed
>>> enough and slightly delayed.
>>>
>>>
>>>
>>> I have tried the following to solve the audio problem:
>>>
>>> 1.  Turning off the SignalLink when I am in SSB mode.  In this case, in
>>> addition to the above-mentioned distortion, I get an audio tone on my
>>> voice
>>> signal which can be heard by whomever I am talking to.
>>>
>>> 2. Disconnecting the cables at the SignalLink but leaving them plugged
>>> into
>>> line in, line out and PTT at the back of the K3 when in SSB. This
>>> does not
>>> fix the problem.
>>>
>>> 3. Disconnecting the cables at the back of the K3 - line in, line out,
>>> PTT.
>>> This solves the problem and I again receive reports of "great audio" 
>>> as I
>>> always have.
>>>
>>>
>>>
>>> It seems like the above symptoms could indicate an "RF in the shack"
>>> problem
>>> though I have not had any RF problems in the past.  My K-Line (K3, P3,
>>> KPA500) is all connected together with grounding strap, however the
>>> SignalLink box has no grounding port, so it is not connected to the 
>>> other
>>> equipment other than with the signal and PTT cables, nor is my computer
>>> connected to the K-Line with grounding strap since it is about five 
>>> feet
>>> away from the K-Line.   My CONFIG: LIN OUT setting on the K3 is NOR
>>> 010, and
>>> I am running the latest firmware, 4.83/2.82.
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