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Date: Fri, 9 Mar 2012 22:13:40 +0000
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From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: DK7FC LF PA schematics
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Stefan -
Your design has a certain amount in common with my 700 Watt half
bridge design http://www.g4jnt.com/137tx.pdf, in particualr the way
the output FETs are driven in parallel from a common drive
transformer.   I took the idea from the Decca transmitters.

But driving the FETs in this way gave a tiny but significant period
when both were on.  I compensated for this in the same way as the
Decca ones did by adding a small centre tapped choke in series with
the top and bottom devices to absorb the transient.

Did you check for or detect any such transients?    I found them very
small and probably non damaging, but the small  choke did not
otherwise affect performance so was used in the circuit as an extra
precaution.   That Tx has been very reliable over the years.

Andy
www.g4jnt.com



2012/3/9 Stefan Sch=E4fer <Stefan.Schaefer@iup.uni-heidelberg.de>:
> LF,
>
> Now i've finally documented my complete LF PA in 2 documents, for those w=
ho
> are interested.
>
> The exciter:
> http://dl.dropbox.com/u/19882028/LF/LF%20H%20bridge%20PA%20Exciter%2C%20D=
K7FC.jpg
> The power part:
> http://dl.dropbox.com/u/19882028/LF/LF%20H%20bridge%20PA%2C%20DK7FC.png
>
> Questions, hints and constructive advice is welcome.
>
> BTW there are further components which complete the TX system here, like =
a
> watchdog savety and PTT sequencer circuit, the IQ transmit converter,
> temperature controlled fans, the automatic variometer. These do not
> necessarily belong to the PA and aren't shown here. A AM Modulator circui=
t
> which allows the PA to easy control the TX power and allows linear modes
> will be added soon.
>
> 73, Stefan/DK7FC
>
>
>