K2 VOX - Straw Poll - Follow up - Long

[Stewart Baker]

Many thanks to all those who responded to my mail.

I was trying to find from those who were using the K2 VOX, their experiences,
and see if they were similar to mine.  Without referring to individual mails the
comments fell into these main categories.

a)  Use CW, don't use SSB, so don't use any VOX !
b)  Don't like VOX on any rig, preferring PTT operation.
c)  Use VOX sometimes, but prefer to the control of PTT.
d)  Mode control to select VOX clumsy.
e)  VOX OK when using headset.
f)   Background noises trigger VOX e.g Phones, Jets, Kids, Mother in Law etc.
g)  VOX cuts off the first syllable of words.
h)  Low VOX sensitivity.
i)   No VOX gain adjustment.
j)   Lack of Anti-VOX.

I think that's covered most, but if I have missed your input please let me know.

Comparing the list with my experiences I found that I agree with most points.
I do not operate CW, and would like to use the VOX on the K2 more frequently.

In my experience the KSB2 board has the following deficiencies in the audio
path:-

1)  Low input sensitivity. For some low output microphones there is insufficient
audio input to the speech compressor U3 leading to a low RF output, and poor VOX
operation. This sometimes results in the first syllable of a word being lost.
External pre-amps may help, but this can lead to other VOX problems.

2) The VOX detection is derived from the speech compressor. Although in
principle this seems like a good idea, however, it means that ANY signal from
the microphone that is strong enough to activate the compression threshold will
trigger the VOX. So the K2 VOX is very susceptible to background noises.
Most other rigs take the processed speech and VOX trigger signals through
separate paths. That way you can have a good amount of speech processing and
still get reliable VOX operation.

3)  Lack of individual adjustment of microphone and VOX gain.
The two adjustments should be independent for the above reasons.

4)  Lack of Anti-VOX. This to me is a real pain. It has put me off using the K2
VOX more than anything else. I'm surprised that this did not get more mentions
in the mail. It really fired me into sending the original mail.

Enough moaning !!!

To cut to the chase. I have spent some time thinking about the KSB2 problems and
after much design work using a circuit simulator have come up with a solution to
address items 1-4. This solution is at a breadboard stage at present (sitting
next to my K2/100), and is working very well. Although it is far from complete I
can give some brief details, so you might care to comment.

It will be a PCB that sits above the audio section of the KSB2, connecting via
approx 6 short wires to the KSB2 PCB. It will require 1 track cut and 1
component to be removed from  the KSB2 PCB.

It will have the following:-
a) An integral tailored microphone pre-amp with Mic gain adjustable from
 0 to +20dB. The input impedance will be 500 ohms.
b) An independently adjustable VOX gain control, driven from the microphone, and
NOT the speech compressor output.
c) A fully adjustable Anti-VOX function that is derived from the speaker output.

As I said there is still some work to be done, but I will keep the group
informed of my progress.

73

Stewart G3RXQ


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[Kurt Cramer]

Stewart I'll buy one!!!!

73, Kurt                        

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[Stewart Baker]

On Thu, 19 Aug 2004 08:40:26 -0500, Tom Hammond wrote:

> Hi Stewart:
> Will the board be thin enough to allow its installation in K2s with the
> KPA100 installed as well?
> Regards,
> Tom Hammond    N0SS
> At 04:12 AM 8/19/04, you wrote:
>> ... snip...
>> To cut to the chase. I have spent some time thinking about the KSB2
>> problems and after much design work using a circuit simulator have come up
>> with a solution to address items 1-4. This solution is at a breadboard
>> stage at present (sitting next to my K2/100), and is working very well.
>> Although it is far from complete I can give some brief details, so you
>> might care to comment.
>> It will be a PCB that sits above the audio section of the KSB2, connecting
>> via approx 6 short wires to the KSB2 PCB. It will require 1 track cut and
>> 1 component to be removed from  the KSB2 PCB.
>> It will have the following:-
>> a) An integral tailored microphone pre-amp with Mic gain
>> adjustable from 0 to +20dB. The input impedance will
>> be 500 ohms.
>> b) An independently adjustable VOX gain control, driven
>> from the microphone, and NOT the speech compressor output.
>> c) A fully adjustable Anti-VOX function that is derived from
>> the speaker output.
>> As I said there is still some work to be done, but I will keep the group
>> informed of my progress.

Good point Tom,

To be honest I had not even considered that. I have my KPA100 installed with the
KAT100 in an EC2 case.

Looking at the clearance left by the KPA100 in the EC2 case I doubt that there
is enough head room above the KSB2 if the amplifier were mounted in the K2.
There are precious few spaces left to put anything.  I need my VOX to work the
way I want, so compromises must be made. I guess the solution could be done in
SMD, but that's rather against the K2 ethic.

73

Stewart G3RXQ

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[Tom Hammond-3]

Stewart:

>To be honest I had not even considered that. I have my KPA100 installed
>with the KAT100 in an EC2 case.
>
>Looking at the clearance left by the KPA100 in the EC2 case I doubt that
>there is enough head room above the KSB2 if the amplifier were mounted in
>the K2.
>
>There are precious few spaces left to put anything.  I need my VOX to work
>the way I want, so compromises must be made. I guess the solution could be
>done in SMD, but that's rather against the K2 ethic.

Actually, I suspect there are a number of folks out there clamoring to try
SMD assembly. Possibly, this could be a small enough project that they
might JUMP at it.

I suspect the project won't be of much use to nearly as many others, if it
can't be somehow implemented in all K2s...

Cheers,

Tom   N0SS

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[n6wg]

Stewart
That sounds like a really worthwhile project.
Please keep us informed of your progress.
I might actually want to fire up my KSB2
with such an "option" to help it out.
73, Bob N6WG
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Guys,
 
I am amazed how dense the K2/100 really is when you take off the right cover to check to see if the cables are pinched.
 
A suggestion would be to use double sided sticky tape and stick on on the KPA100 shield with some sort of header pins to unplug it when you remove the KPA100.  Place it on the shield where it could fit in the K2 box.  I am not sure what would happen to any kind of RF into the audio stage but since everything is so close in there anyway it might not be a problem.  If you have some controls...gain, antivox, etc....that might be an issue that is insurmountable.
 
Just random thoughts from a random guy
 
Lee - K0WA
 
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