[Kenwood] TS-940 Audio Problem

[Rob]

If there is a carrier offset adjustment it may be that it is set too  
far above the filter skirt on LSB.

I don't know much at all about the 940 however I believe it generates  
SSB the old analog way with a balanced modulator and upper and lower  
sideband filters.

There may be (you should probably have the service manual for this)  
little trimpots in the rig you adjust to "move" the suppressed carrier  
closer to, or farther from, the IF xtal filter that also is used on  
transmit to cut out the opposite sideband and residual carrier from  
the b.m.  These trimpots can be tricky to adjust however.  get the  
carrier too close  to the -6 dB part of the filter response curve and  
you have carrier coming through on transmit.  you also have to watch  
the USB to make sure you have balance in tx audio response and carrier  
supression on both USB and LSB.  This is best done with a decent PC  
powered DSP receiver that can be used for ham purposes as a spectrum  
analyzer.  One of these units from RF Space, or Softrock will work.    
If nothing else tx into a dummy load and listen on a good ham receiver  
like a separate Kenwood rig, a TS870 for example switching between  
side bands.

If the 940 is a later microprocessor controlled rig the carrier offset  
may be set up through a front panel menu adustment scheme which is a  
lot easier to perform.

Or, you could forget all this and operate the rig on AM :  )

GL and 73

Rob
K5UJ




On Nov 2, 2009, at 6:34 PM, Dennis Klipa wrote:

> When my friend, John, transmits on LSB on his TS-940 with his MC-60
> microphone, it sounds like all of the bass has been stripped from  
> his voice,
> as if there were a narrow band filter in the mic circuit. This is  
> true on
> all bands.  We have taken his microphone and put in on my TS-940 and  
> it
> sounds great, according to on air reports.  It is a little more  
> sensitive
> that my MC-60 but we only have to turn down the mic gain one notch  
> to keep
> the ALC within range with his mic on my 940.  It doesn't matter which
> impedance you select on the mic or whether the preamp in the mic  
> base is on
> or off, the audio still sounds bad.   The speech processor is turn
> off.  Turning it on only makes matters worse.  So it is not the  
> microphone.
>
> When we turn down the Power down on his rig to about 5 watts out, the
> audio quality increases but only slightly.
>
> We have tried LSB, USB, AM and FM modes.   The problem is only  
> present on
> LSB.
>
> The obvious adjustments to check are:
> 1.  SSB Mode Frequency Response
> 2. Supply Voltages
> 3. Carrier Suppression (balanced)
>
> But before I open the cover, I wanted to find out if anyone had  
> experienced
> this problem before or has any suggestions on what to look for.
>
> Thanks, es 73,
> Dennis, N8ERF
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