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K2 - SSB TX audio

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ON4WIX

K2 - SSB TX audio

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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Stewart Baker

Re: K2 - SSB TX audio

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
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com

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Jim Sheldon

RE: K2 - SSB TX audio

When I first installed the KSB2 in my K2 a couple of years ago, I started
looking for a microphone to test it with. I found the 600 ohm CB style
dynamic microphone from an old Tempo VHF-1 2 meter rig that I had
disassembled for parts, and figured it would be good enough for a test at
least. Those old CB type 600 ohm microphones had pretty big magnets in
them, and were capable of several hundred millivolts of audio output. This
particular one drives my K2 very nicely. I borrowed a Heil hand microphone
from someone local that had one, built an external adapter so I could switch
rapidly between the two and ran "on-the-air" comparisons. Much to my
surprise, the CB type microphone had better sounding audio than the Heil (on
my K2) and everyone that I ran the test with, both local and even several DX
stations told me to put the Tempo microphone back on and leave it alone.
That was 2 years ago, and since, when I actually do run the K2 on SSB
(rarely) I keep getting comments on the audio. More than one person has
told me he thought I had a Heil Gold Line microphone on it because it
sounded so nice.

I'm not saying you're going to get the same results, but rather than spend
big bucks for a "Super Microphone", at least give one of the older CB type,
non-amplified, 600 ohm dynamic microphones which you can usually pick up for
a couple of dollars at a hamfest or electronic flea market a try. I'd bet
that if you have the BFO set correctly, you'll have nearly the same results
I did. At least, you'll have sufficient audio to drive the KSB2 and not
have to modify the radio to beef up the circuitry.

Jim Sheldon
W0EB
K2 #4338

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Stewart Baker
> Sent: Sunday, March 12, 2006 7:21 AM
> To: ON4WIX; [hidden email]
> Subject: Re: [Elecraft] K2 - SSB TX audio
>
>
> 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 _______________________________________________
> > Elecraft mailing list
> > Post to: [hidden email]
> > You must be a subscriber to post to the list.
> > Subscriber Info (Addr. Change, sub, unsub etc.):
> > http://mailman.qth.net/mailman/listinfo/elecraft
> >
> > Help: http://mailman.qth.net/subscribers.htm
> > Elecraft web page: http://www.elecraft.com
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>