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Re: LF: Re: G3WSC/P acty

To: [email protected]
Subject: Re: LF: Re: G3WSC/P acty
From: "g3kev" <[email protected]>
Date: Wed, 12 Apr 2000 20:44:00 +0000
Organization: Netscape Online member
References: <[email protected]> <[email protected]>
Reply-to: [email protected]
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Dave wrote:

Eh what??

> Square wave generators/dividers and class D/E amplifiers are fine for
> small antennas and low erp but NOT SUITABLE for larger antennas and high
> power. An abundance of LPF and BP filters might help to clean up the
> signal.

I think you're getting confused with high levels of harmonic output, which
class D amplifiers can suffer from if not properly filtered, and sideband
energy from fast rise and fall times of the transmitted envelope
That is what I said about filtering, the LPF if designed to cut off just above
the operating frequency will inhibit the harmonics. Most of the recent designs
are divider systems(square waves)followed by mosfets and because of their
nature comprise 3/5/7 and beyond odd order harmonics.
If there is inadequate filtering following the mosfets then the output is part
square wave.

.
LPF will NOT help!
That is exactly what a LPF filter is for ie to reduce or suppress harmonics
between an amplifier and the antenna. What did you think a LPF was for.????
The ARRL handbook explains exactly what they do, and gives all the design
information for all applications.


This can happen with any kind of amplifier, I key my class D PA with a
tailored rise and fall, series device.
It CAN happen to any class of amplifier but a sinewave signal source fed to a
well designed linear amplifier will be less prone to harmonic problems,
especially a tube amplifier.


Oh, and by the way, they were using a linear amplifier!
(It was a little bit clicky though...)
Glad you agree there were CLICKS. They were very noticeable on the LF side of
the transmission.
The signal spread was 250 hz and as I said MM0ALM was 2 db stronger but a
clean signal using his tube amplifier. I hope they get it cleaned up before
the next visit.
If it was supposed to be  LINEAR is was obviously NON linear, the keying
seemed hard.


Dave 'YXM.



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