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From: "n8tl" <n8tl@woh.rr.com>
To: <rsgb_lf_group@blacksheep.org>
References: <001701c7b9ab$5333d340$6d177ad5@w4o8m9>
Date: Thu, 28 Jun 2007 19:23:37 -0400
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Subject: LF: Re: 500kHz class D TX design
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Hi Jim:

I would appreciate a copy of  the schematic...at your convenience.  Send to 
n8tl@woh.rr.com .

Thanks in advance.

Cheers,

Tom N8TL
----- Original Message ----- 
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, June 28, 2007 1:39 PM
Subject: LF: 500kHz class D TX design


> 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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> 10:56 AM
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