[Elecraft] K2 - SSB TX audio

[Stewart Baker]

Hi Glenn,

The audio gain on the KSB2 board is marginal. Some get away with it, but others 
do not. Your diagnosis of the effect of the compressor chip noise gate is 
probably correct. This affects not only the level of the audio vs RF in the 
balanced modulator, but also the VOX operation.
I have added an internal (9dB) one transistor pre-amp with some bandwidth 
tailoring. This got rid of the 2 main problems when using the K2 on SSB.

73
Stewart G3RXQ

On Sun, 12 Mar 2006 13:34:05 +0100, ON4WIX wrote:
> Hi all,
>
> another day, another question it seems...
>
> I finished building the KSB2 board yesterday and installed it in my K2 s/n
> 5361.
> All test results were OK. I changed the BFO settings as per the manual
> instructions.
>
> This morning I made a recording of my transmissions. The K2 is hooked up to a
> dummy load, receive audio is fed from my TS-570 into the computer. The
> soundcard is not overloaded, checked that by recording a few signals off air
> with my TS-570.
>
> I noticed that my audio sounds very 'gritty'. RF out reading seems OK on the
> K2, ALC is just flashing 1 LED.
> Speaking about 2 inches from the mic it seems the audio is cutting out in a
> very rapid fashion. It sounds like a noise gate switching on and off very
> quickly. This causes sibilants to sound almost as white noise. Speaking into
> the microphone very closely (lips touching mike) the noise gating effect is
> much less pronounced.
>
> I read that the KSB2 compressor chip also has a noise gate. This makes me
> wonder whether there is not enough drive from the microphone, resulting in an
> audio level that's right on the threshold of the noise gate. Do I need to
> crank up my mic audio before it enters the K2? I do have a simple 741-based
> preamp lying around somewhere but I'm a bit hesitant to press it into service
> sitting next to a transmitter.
>
> Microphones used for this test were a Kenwood hand mike (the one originally
> supplied with my TS-570) and a Heil BM-10 with an HC-5 cartridge. Both
> exhibited similar behaviour.
> I recorded my tests with these two mikes. If anyone wants to receive these
> recordings in order to evaluate the problem please send me a mail direct.
> Address is <mycall>@skynet.be
>
> I have not tweaked the BFO frequencies for optimal audio yet. It would seem
> to me that this is not a BFO/bandpass filter related problem given the choppy
> audio. It's not really a problem that's situated in the frequency domain.
>
> Anyone had a similar experience?
>
> Have a very nice Sunday
>
> 73 de Glenn ON4WIX
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