[Elecraft] VOX Lockup

[Stewart Baker]

Hi John,

I had a similar problem a while back, where, after a time when triggered the VOX 
would stay on. I finally traced the problem to a defective DAC IC (U2 MAX522).
This supplies a threshold voltage to comparator U4. I found that the voltage out 
of U2 pin 5 was drifting with temperature. Eventually it got so close to the 
voltage out of U3 pin 7 that ,when triggered the VOX locked up.
Fitting a new IC cured the problem.

To help you identify whether this is your problem, here are some voltage 
measurements from my KSB2. These are the differential voltage readings 
between U4 pins 2 & 3.

SSBA =1 =76mV
SSBA =2 =74mV
SSBA =3 =50mV

73
Stewart G3RXQ


On Sat, 31 Dec 2005 07:19:46 -0500, John Huffman wrote:
> I'm using a new microphone with my K2/100.  It's a desk mike (Ten Tec 706) and
>
> I'm using the VOX a lot more than in the past.  Had a strange thing happen
> last
> night.
>
> The band was 75 meters and I had the attenuator on and the RF gain backed off
> by
> about 75%.
>
> The VOX worked fine during my net transmission.  However, afterward I was
> listening and a strong station seemed to trigger the VOX.  I unplugged the
> mic,
> but the K2 stayed in transmit mode.  I had to turn off the K2 to stop
> transmitting.
>
> I know the K2 VOX doesn't have anti-VOX, but I was wearing headphones.
> Nothing
> was coming through the speaker.
>
> Any similar experiences or solutions?
>
> 73 de NA8M
> John
>
>
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