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Date: Thu, 28 Jun 2007 19:59:44 +0100
From: "Roger Lapthorn" <rogerlapthorn@gmail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: 500kHz class D TX design
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James,

Where can we find this schematic please?

73s
Roger G3XBM

On 28/06/07, James Moritz <james.moritz@btopenworld.com> wrote:
>
> Dear LF Group,
>
> I drew up a circuit diagram of my new 500kHz transmitter design in case
> anyone is interested.
>
> It uses a "half-bridge" voltage-switching class D PA with complementary N
> and P channel mosfets. The idea of this is that the push-pull design
> minimises 2nd harmonic levels at around 1MHz, and the complementary
> mosfets
> simplify the gate drive requirements somewhat. It uses cheap IRF520 and
> IRF9520 devices, and produces a maximum output of about 11W with 13.8V DC
> supply. It can easily run at different power levels by changing the number
> of turns on the output transformer. I included DC current limiting  in the
> keying circuit, which allows the PA to operate into open, short, and
> reactive loads without apparent distress.
>
> It has a VFO based on a 4MHz ceramic resonator and divide-by-8 counter.
> This
> covered the whole band with several resonators I tried, and drifts by a
> few
> hertz per hour, which is satisfactory for most purposes.
>
> The circuit diagram is the basic CW transmitter for now. I have also added
> various other bits and pieces such as variable output power, FSK for DFCW,
> and a RF voltage/current/phase output metering system for easy antenna
> tuning, but will have to draw  these up later. The image is slightly too
> big
> to be sent via the reflector, but if anyone would like a copy, let me know
> and I will e-mail it direct.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>

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James,<br><br>Where can we find this schematic please?<br><br>73s<br>Roger G3XBM<br><br><div><span class="gmail_quote">On 28/06/07, <b class="gmail_sendername">James Moritz</b> &lt;<a href="mailto:james.moritz@btopenworld.com">
james.moritz@btopenworld.com</a>&gt; wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Dear LF Group,<br><br>I drew up a circuit diagram of my new 500kHz transmitter design in case
<br>anyone is interested.<br><br>It uses a &quot;half-bridge&quot; voltage-switching class D PA with complementary N<br>and P channel mosfets. The idea of this is that the push-pull design<br>minimises 2nd harmonic levels at around 1MHz, and the complementary mosfets
<br>simplify the gate drive requirements somewhat. It uses cheap IRF520 and<br>IRF9520 devices, and produces a maximum output of about 11W with 13.8V DC<br>supply. It can easily run at different power levels by changing the number
<br>of turns on the output transformer. I included DC current limiting&nbsp;&nbsp;in the<br>keying circuit, which allows the PA to operate into open, short, and<br>reactive loads without apparent distress.<br><br>It has a VFO based on a 4MHz ceramic resonator and divide-by-8 counter. This
<br>covered the whole band with several resonators I tried, and drifts by a few<br>hertz per hour, which is satisfactory for most purposes.<br><br>The circuit diagram is the basic CW transmitter for now. I have also added
<br>various other bits and pieces such as variable output power, FSK for DFCW,<br>and a RF voltage/current/phase output metering system for easy antenna<br>tuning, but will have to draw&nbsp;&nbsp;these up later. The image is slightly too big
<br>to be sent via the reflector, but if anyone would like a copy, let me know<br>and I will e-mail it direct.<br><br>Cheers, Jim Moritz<br>73 de M0BMU<br><br><br></blockquote></div><br>

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