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List:       elecraft
Subject:    RE: [Elecraft] VOX clicks with Yaesu MD-100 microphone
From:       "Fletcher, Paul" <Paul.Fletcher () nnc ! co ! uk>
Date:       2004-08-31 8:55:07
Message-ID: 2A6DC2A9887100488AC1519ACFCF27B0A99713 () nnc ! co ! uk
[Download RAW message or body]

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:stewart@baker.nildram.co.uk]
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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