VOX clicks with Yaesu MD-100 microphone

[Stewart Baker]

Here's a good one...

While testing the latest version of my Anti-VOX board I got reports saying that
my SSB signal was "clicky"on VOX. I thought the worst...

After much investigation it turned out to be nothing to do with my board, or the
K2 for that matter.

Some "Engineer" decided when he designed the MD-100 microphone tone control
circuitry to route the PTT line clean through the center of it's analog
circuits.

The K2 uses the PTT line on VOX for TX/RX changeover. The effect I was getting
was the low to high transition at the end of the VOX delay period being coupled
into the microphone audio, causing a "click".

The solution was simple. I removed the PTT wires where they connect to the main
PCB in the microphone base, and reconnected them separately. End of problem.
It is possible that other microphones may be similarly afflicted.
If anyone wants more detail, please shout.

73

Stewart G3RXQ

B.T.W Version 3 of the Anti-VOX is working well.

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[Stewart Baker]

On Mon, 30 Aug 2004 13:44:02 -0400, Don Wilhelm wrote:
> Stewart,
> If I understood the root cause of your 'problem' correctly, that is a good
> indicator that you have created a very sensitive VOX.  In that case, it may
> even my work with my normal voice - I will be looking forward to trying it
> soon.
> 73,
> Don W3FPR

Hi Don,

The subject of the K2 VOX sensitivity is a complex one, and even after
considerable investigation I don't pretend to understand it fully.

What is important is to get sufficient (but not too much) audio voltage from the
microphone into the KSB2. This may mean using a pre amp. If this audio voltage
is not sufficient, both the VOX operation and SSB output power will suffer
equally.

My original intention when creating an Anti-VOX capability was to incorporate a
pre amp in the design and use this to get more mic audio and a separate feed
into the VOX detection circuit. Although this worked OK at low power and on the
lower frequencies it was very susceptible to RF and because my circuit was
separate from the KSB2 PCB tracking, rather prone to instability.

For the time being I have put that idea to one side and concentrated on the
Anti-VOX problem, which is much easier to solve.

I now have a fully working Anti-VOX, but to get reliable VOX operation I use a
20dB mic pre amp with the MD-100 and use the K2 set to mic input position 2 with
the  compression set to 4:1. With this set up the sensitivity is about right and
it gives me 100% VOX operation with no tripping from the speaker audio.

As I said I do not fully understand the internal (firmware) workings of the K2
VOX, namely why I have to use 3:1 or 4:1 compression to ensure that the VOX does
not drop out when the 1:1 setting provides sufficient audio to activate it.
There should be more than enough audio to prevent this drop out.
It would help greatly to have a bit more of an insight into the design.

The microphone 'click' situation showed that I have sufficient mic gain, but for
a while everything in the K2, and in my design was suspect. WHEW !

73

Stewart G3RXQ


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[Fletcher, Paul]

Stewart,

Heard you several times on 3.727 over the last few weeks (and spoken to you
in the past) and I must say your audio is v. nice (usual British
conservative statement!) Do you have any details of the work you have
carried out published? Would make interesting reading.

Apologies if your info has bone out via the reflector only my mailbox
cleanup has conveniently deleted everything over a couple of days old.

Regards,
Paul.

-----Original Message-----
From: Stewart Baker [mailto:[hidden email]]
Sent: 31 August 2004 08:31
To: Elecraft Reflector
Subject: Re: [Elecraft] VOX clicks with Yaesu MD-100 microphone


On Mon, 30 Aug 2004 13:44:02 -0400, Don Wilhelm wrote:
> Stewart,
> If I understood the root cause of your 'problem' correctly, that is a good
> indicator that you have created a very sensitive VOX.  In that case, it
may
> even my work with my normal voice - I will be looking forward to trying it
> soon.
> 73,
> Don W3FPR

Hi Don,

The subject of the K2 VOX sensitivity is a complex one, and even after
considerable investigation I don't pretend to understand it fully.

What is important is to get sufficient (but not too much) audio voltage from
the
microphone into the KSB2. This may mean using a pre amp. If this audio
voltage
is not sufficient, both the VOX operation and SSB output power will suffer
equally.

My original intention when creating an Anti-VOX capability was to
incorporate a
pre amp in the design and use this to get more mic audio and a separate feed
into the VOX detection circuit. Although this worked OK at low power and on
the
lower frequencies it was very susceptible to RF and because my circuit was
separate from the KSB2 PCB tracking, rather prone to instability.

For the time being I have put that idea to one side and concentrated on the
Anti-VOX problem, which is much easier to solve.

I now have a fully working Anti-VOX, but to get reliable VOX operation I use
a
20dB mic pre amp with the MD-100 and use the K2 set to mic input position 2
with
the  compression set to 4:1. With this set up the sensitivity is about right
and
it gives me 100% VOX operation with no tripping from the speaker audio.

As I said I do not fully understand the internal (firmware) workings of the
K2
VOX, namely why I have to use 3:1 or 4:1 compression to ensure that the VOX
does
not drop out when the 1:1 setting provides sufficient audio to activate it.
There should be more than enough audio to prevent this drop out.
It would help greatly to have a bit more of an insight into the design.

The microphone 'click' situation showed that I have sufficient mic gain, but
for
a while everything in the K2, and in my design was suspect. WHEW !

73

Stewart G3RXQ


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