Re: LF: Re: Re: DECCA 5501 tx

[Andy Talbot <andy.g4jnt@googlemail.com>]

Those transmitters consist of a full bridge output, where the connection to the series LC is hard switched to alternately +V or -V.  The result is a low impedance voltage source driving the tank.     Such a transmitter requires a series tuned circuit at Fo to select the wanted component while appearing as a high impedance to all harmonics.   So you will not see any drain (source of the upper device) waveform oteh rthan the square wave outptu plus any incidental small spikes, that ideally shouldn't be there.

 

Contrast with a class E that alternately switches to ground then opens, allowing the voltage peak to fly off to whatever the C-L-C network allows it to reach.  

 

Tnx for the replies to my - originall light hearted - comment about needing a 1kW PA.  It looks simpler than at first thought, so I just  'may' get round to adding it to the project to-do list (after retirement / quitting - getting ever closer).  The 137kHz 700 Watt jobbie was straightforward enough - it was uncontrolled transients that caused problems there as I was running from such a high Vcc (340 Volts) that layout mattered.    Keeping with a 50V rail ought to simplify things somewhat.

 

Andy
www.g4jnt.com

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2010/1/13 mal hamilton <g3kevmal@talktalk.net>

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.
It would be interesting to observe the switching wave form while adjusting
L/C for resonance instead of just peaking for max output.
mal/g3kev


----- Original Message -----
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, January 13, 2010 3:26 PM
Subject: LF: Re: DECCA 5501 tx


> Dear Mal, LF Group,
>
> In a class D circuit, optimum switching conditions occur more or less when
> the tank circuit is resonant.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
> -- Original Message -----
> From: "mal hamilton" <g3kevmal@talktalk.net>
> To: "rsgb" <rsgb_lf_group@blacksheep.org>
> Sent: Wednesday, January 13, 2010 11:38 AM
> Subject: LF: DECCA 5501 tx
>
>
> Does anyone know if the series L and C was tuned for resonance at the
> operating freq or meant to be adjusted for optimum switching
characteristics
> like in class E
> mal/g3kev
>
>