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Message-ID: <11F4F2A4333B47F98182FC8461A9BA47@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <001201ca9444$ed415810$0301a8c0@your91hoehfy9g> <3C7515D8E8B4467A8CF7A04C8C26F2C2@JimPC> <003301ca946d$3f750460$0301a8c0@your91hoehfy9g>
In-Reply-To: <003301ca946d$3f750460$0301a8c0@your91hoehfy9g>
Date: Wed, 13 Jan 2010 18:54:26 -0000
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Subject: LF: Re: Re: Re: DECCA 5501 tx
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Dear Mal, LF Group,

G3KEV wrote:

> Tnx Jim for reply, but since a class D with a resonated output L/C becomes 
> a
> single frequency tx it is getting close to class E design.

All of these circuits which depend on a tuned tank circuit of some sort 
(class C, D, E, F...) are essentially single frequency devices, although 
often the tank loaded Q can be fairly low, and so accomodate a modest 
frequency change without re-tuning. Differences between class D and E are:

-Class D designs of the "Decca" voltage-mode type are "zero-current 
switching", i.e. the output devices switch the voltage when the load current 
sine wave reaches its zero points, which reduces switching losses. (the 
push-pull G3YXM/G0MRF circuits are more-or-less the complementary, 
current-mode, zero-voltage switching type). Class E cleverly arranges things 
so that both voltage and current are zero when switching occurs, further 
reducing switching losses.
-Class D are symmetrical circuit topologies with symmetrical waveforms at 
the output, while the basic class E circuit is single-ended with 
asymmetrical waveforms.

> It would be interesting to observe the switching wave form while adjusting
> L/C for resonance instead of just peaking for max output.

As Andy says the Decca-type switching waveform is ideally always a square 
wave, irrespective of load impedance. The load current, observed with a 
current transformer, is always virtually a sine wave. The effect of 
mis-tuning is that the voltage and current waveforms get out of phase with 
each other.

Cheers, Jim Moritz
73 de M0BMU