Message-ID: <DEC900E8839742E98523BCFAB2F6D863@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <4E355332.6010107@iup.uni-heidelberg.de> <CAA8k23QgKD0vtr2znFwjdqSLWKZy7g3vbdDfM9zJfc4vqQRFLA@mail.gmail.com> <4E355927.4010905@iup.uni-heidelberg.de> <4E355CF9.8020504@iup.uni-heidelberg.de> <B00F5CD93B3B475CB3B34224C6FD1CA7@AGB> <101744BA6E9F4F649EF3AA71661C8397@JimPC>
In-Reply-To: <101744BA6E9F4F649EF3AA71661C8397@JimPC>
Date: Mon, 1 Aug 2011 15:59:04 +0100
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Subject: Re: LF: frequency doubler and divider
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Complimentary   my  dear  Watson   ...... hi

G..


--------------------------------------------------
From: "James Moritz" <james.moritz@btopenworld.com>
Sent: Monday, August 01, 2011 12:48 AM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: frequency doubler and divider

>
> Dear Graham, Stefan, LF Group,
>
> ----- Original Message ----- 
> From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
>
>
>>Has anyone  looked  closely  at  Jim's  Class  D/E  EER   tx ?
>
> Well, Jim has ;-) All that is used is a limiting amplifier to "square up" 
> the input sine wave. For a push-pull PA, anti-phase square wave gate drive 
> is obtained simply using an inverter. There is no requirement to multiply 
> or divide the frequency. To obtain a 50% duty cycle square wave, the 
> limiting thresholds need to be symmetrical around the average value of the 
> input waveform. In the EER transverter, I used a transistor differential 
> pair to provide a well-defined symmetrical limited waveform. The output of 
> the differential amp is fed through some CMOS gates to increase the gain 
> and make the output "square-er". You could use a voltage comparator 
> instead, but it has to be a fairly fast one to avoid significant asymmetry 
> in the output waveform due to differences in rise/rall times with positive 
> and negative going signals, and other effects.
>
> This works fine provided your signal source generates a symmetrical 
> waveform, i.e. the wanted signal frequency with or without odd order 
> harmonics, such as a sine wave or a square wave. If the waveform is 
> asymmetrical (containing substantial levels of even-order harmonics), such 
> as a rectangular waveform with non-50% duty cycle, or contains 
> non-harmonic components (e.g. unwanted mixing products), then a bandpass 
> filter is needed to remove the unwanted components. But most practical 
> signal generation schemes do not contain very high levels of unwanted 
> frequency components close to the signal frequency, so a simple single LC 
> tuned circuit with low Q is an adequate bandpass filter.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>
>