Message-ID: <38F57A62.4440670F@netscapeonline.co.uk>
Date: Thu, 13 Apr 2000 07:42:26 +0000
From: "g3kev" <g3kev@netscapeonline.co.uk>
Organization: Netscape Online member
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Re: G3WSC/P acty
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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.
> LPF will NOT help!

I DID NOT SAY A  LPF  would cure key clicks. I said a LPF would stop
HARMONICS, especially odd harmonics 3/5 etc. from the type of divider/mosfet
amplifiers used on 136 khz. You need a good multi pole LPF with these type of
amplifiers especially with large antennas.

KEY CLICKS  were also mentioned in the message about the G3WSC/P transmitter,
and as you say this is due to fast rise times/timing and requires a different
type of filter/circuit.
I was merely pointing out that besides the key clicks, there was a possibility
of radiating odd harmonics if not properly filtered because of the intensity
of the signal with a large antenna.
If more power is to be used from such an installation, a bad situation will
get worse.

G3KEV


>
> This can happen with any kind of amplifier, I key my class D PA with a
> tailored rise and fall, series device.
>
> Oh, and by the way, they were using a linear amplifier!
> (It was a little bit clicky though...)
>
> Dave 'YXM.