[Elecraft] VOX sensitivity K2/KSB2

Tue Aug 5 03:04:01 2003

 On Mon, 04 Aug 2003=
 11:14:34 -0400, Dale Boresz wrote:

=
 >g3pjt wrote:
=
 >
=
 >>Hi
=
 >>
=
 >>Does anyone know if it is possible to increase the VOX=
 sensitivity

=
 >>on the
=
 >>KSB2?
=
 >>
=
 >>But NOT by :
=
 >>- increasing the audio gain/level input ( or compressor=
 setting)

=
 >>
=
 >>
=
 >>Thanks
=
 >>
=
 >>Bob G3PJT
=
 >>
=
 >>
=
 >>
=
 >Bob,
=
 >
 >One=
 of your countrymen, Stewart, G3RXQ submitted a very=
 interesting

=
 >posting to the list on 6/23/2003 with details concerning a=
 number of

=
 >SSB-related issues, among them increasing compression level=
 (which I

=
 >have done, and which works incredibly well with the Heil=
 HC-5

=
 >element),
 >and=
 also a way to improve the VOX sensitivity. If you wish to=
 locate

=
 >the
=
 >original posting, the subject line was: {quot}SSB Mods=
 (long){quot} Attached
=
 >below
 >is=
 the snippet concerning the VOX sensitivity (which I have=
 not

=
 >tried
=
 >since I don't use VOX):
=
 >
=
 >##### BEGIN SNIPPET FROM Stewart - G3RXQ posting of=
 6/23/2003 #####

 >c)=
 On my K2 the level of signal into comparator amplifier U4 pin=
 2

 >was=
 marginal when compared to ALC THR from the DAC U2. This=
 meant

=
 >that the VOX operation was not consistent.
 >The=
 level from U3 is fixed 1:1) due to /COMP0 being at 0V during=
 RX

=
 >which means that no amount of reasonable mic gain will=
 improve the

=
 >VOX. Two options presented themselves for
=
 >increasing the signal into U4. The first was to put a=
 small

=
 >amplification stage in circuit. This was discounted because=
 of space

=
 >constraints. The other which was adopted was to=
 {quot}wet{quot}
 >the=
 compressor by allowing a very small amount of compression=
 to

=
 >occur in the RX state. This is done by a small value=
 resistor (4.7k)

 >in=
 series between /COMP0 and U3 pin 6.

 >I=
 cut the track from U1/RP5 and U3 pin 6 where it runs along=
 the

=
 >left side of the KSB2. On the underside of the board I=
 =A0connected

 >the=
 4.7k resistor between RP5 pin 1 and U3 pin 6.

=
 >This value can be increased, but remember the K2 has no=
 Anti-VOX.

 >The=
 VOX now works brilliantly.

=
 >##### END SNIPPET FROM Stewart #####
=
 >
 >73,=
 Dale / wa8sra

=
 >
=
 >
=
 >
=
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=

=
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=

http://www.elecraft.com

=
 Hi=

 The VOX mod I made is largely=
=
  of=

 Since my previous post I have=

 5 k preset pot. The VOX=

 73

 Stewart G3RXQ

 -- The Bakers'=

 -- [email protected]=

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