Hi Alan,
In fact, the spectrogram that I posted shows strong key clicks of Class D
amplifier on the signal to 472.1 kHz.
Also the linear amplifier at 472.5 KHz in the spectrogram shows key clicks
but lower.
On the other hand you can see that my signal at 473.3 is very clean without
key clicks.
Many hams have asked me how it is possible that with a switching amplifier
there are no key clicks.
The answer is that I have taken a different approach by the schemes that are
on web and the result
you can see yourself.
It is very important to dampen all transients during switching from
interdiction to conduction and vice versa.
I had to work a lot but at the end I got a very clean TX.
73, Fausto IK4NMF
----- Original Message -----
From: "Alan" <[email protected]>
To: "Fausto Coletti" <[email protected]>
Sent: Monday, July 27, 2015 5:21 PM
Subject: Re: [Elecraft] K3: 630m amplifiers
Hi Fausto,
The term "class D" can mean many different things. As long as a class-D
amplifier uses some means to preserve the modulation envelope (the shape
of the amplitude) then it would work fine for CW. But if the input CW
signal is hard-limited then the wave shaping will be lost and key clicks
will result.
It's not an issue for FSK digital modes, because the amplitude is
constant, so hard-limiting has no effect. But CW is actually a form of
amplitude modulation so it needs a linear amplifier.
73,
Alan N1AL
On 07/27/2015 12:30 AM, Fausto Coletti wrote:
It depends on how you made the amplifier.
I produce some models of amplifiers, of different powers, all in
switching operation.
Attached an image of the DK7FC grabber, you can see at 472.1 KHz the
spectrogram of
a German station that use a class D amplifier, at 472.5 an Italian
station that use a 400W
tube linear amplifier and at 473.3 there is my signal with my QRO+
switching PA.
I can assure that I often find local stations operating at 250-300 Hz
from my frequency
that are not minimally disturbed
I do not think that a linear amplifier is so better.
I also made a 100W output amplifier specifically designed for the K3.
This amplifier runs at 12 volt.
All my PA need an input signal (adjustable) from -10dBm to + 20 dBm
73, Fausto IK4NMF
----- Original Message ----- From: "Alan" <[email protected]>
To: <[email protected]>
Sent: Monday, July 27, 2015 6:32 AM
Subject: Re: [Elecraft] K3: 630m amplifiers
> CW would be another mode that would not need a linear amp I think.
No, CW requires a linear amplifier. CW is not constant-amplitude -
the amplitude changes every time you open or close the key. A class-C
amplifier would mess up the key shaping, causing key clicks.
Any true FSK or MSK signal should not be bothered by a non-linear
amplifier. The only caveat I can think of is that the amplitude of an
AFSK signal may have some ripple on it to the extent that the passband
of the transmit crystal filter is not flat. But I doubt that's a
significant issue.
Alan N1AL
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