[Elecraft] K3: 6M SSB audio hash

[Joe Subich, W4TV]

> I have not investigated the W2IHY equipment, but my understanding 
> is that it is setup primarily for pro mics which use balanced AF 
> lines for the mic audio.  My suspicion is that there is something 
> awry with the balanced to unbalanced arrangement when used with 
> unbalanced line microphones such as you have there.

There is a significant problem in using balanced input with any 
"amateur mic" - including Icom, Kenwood, Yaesu and Heil.  Yaesu, 
Kenwood and Heil connect the shield of the mic cable to the mic 
return and not chassis (ground).  Icom uses the shield as the 
mic return.  

When the shield of the mic cable is tied to the low side of a 
balanced input, RF that SHOULD go to ground/chassis is forced 
through the mic preamp instead.   With the shield tied to the 
mic return there is effectively a 10' piece of wire (antenna) 
connected to the mic input unless the mic return is tied to 
the chassis and the chassis is connected to a solid RF ground. 

73, 

   ... Joe, W4TV 
 







> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Don Wilhelm
> Sent: Friday, June 06, 2008 6:17 PM
> To: James C. Hall, MD
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3: 6M SSB audio hash
> 
> 
> Jamie,
> 
> The Heil headset will plug directly into the rear panel jacks 
> - why not 
> give that a try as an added piece of evidence that it is not 
> the microphone.
> 
> Most likely, something is being picked up on those long microphone 
> cables and is not a K3 problem at all.  Are all the mic cables 
> shielded?  Are all the cable shields connected to the 
> plug/jack shell?  
> They should be.
> 
> I have not investigated the W2IHY equipment, but my understanding is 
> that it is setup primarily for pro mics which use balanced AF 
> lines for 
> the mic audio.  My suspicion is that there is something awry with the 
> balanced to unbalanced arrangement when used with unbalanced line 
> microphones such as you have there.
> 
> As far as why it shows up only when the PA turns on, I can only 
> speculate there too, but remember that there is more gain in the 
> transmit stages when the PA turns on, and that added gain may 
> make any 
> small AF line pickup more pronounced in your transmit signal.  If it 
> were from RF coupling into the audio, it would vary smoothly from low 
> power to high power and all RF levels in between - you indicated only 
> that it was there with the PA on, but did not say that it got 
> worse as 
> power was increased.
> 
> 73,
> Don W3FPR
> 
> James C. Hall, MD wrote:
> > Bob:
> >
> >  
> >
> > As a follow up, I doubt it's the Goldline mic/cable itself, 
> as I get the
> > same hash with a Heil headset plugged into the switcher. 
> >
> >  
> >
> > 73, Jamie
> >
> > WB4YDL
> >
> >  
> >
> >
> > From: James C. Hall, MD [mailto:nwtcc at earthlink.net]
> > Sent: Friday, June 6, 2008 04:27 PM
> > To: elecraft at mailman.qth.net
> > Subject: [Elecraft] K3: 6M SSB audio hash
> >
> > Hello: I've noticed some audio hash on my SSB signal on 6M 
> only when the PA
> > relay kicks in at 13 watts. My long microphone cable goes to a
> > Multi-Switcher -> W2IHY Noise Gate/Equalizer -> Heil 
> Goldline microphone.
> > This completely disappears when I use a Kenwood hand mike 
> direct to the K3.
> > Thinking that this was a classic "RF on the line" problem, 
> I clipped on
> > multiple ferrite chokes with many turns on the cable coming 
> from the K3, the
> > Goldline mike, and in between the switcher on noise gate. 
> This didn't even
> > slow it down ! Hmmm. Interestingly when the PA relay is off 
> at 8 watts,
> > there is absolutely no hash. For now, I'll just use the 
> hand mike on 6M
> > (which requires a bit more mike gain) to keep a clean 
> signal. Has anyone
> > else noticed this ? Got a solution ? 73, Jamie WB4YDL
> >   
> >
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