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<H1 align=center><FONT face=Perpetua color=#009900><FONT face=SerpentineDBol>A
100 Watt CW Transmitter for the 500 kHz Band</FONT></FONT></H1>
<P align=center><FONT color=#0000ff size=+2><B><FONT color=#ff0000>André
Kesteloot</FONT> <FONT color=#3399ff>N4ICK</FONT> </B></FONT><BR><FONT
color=#ff00ff>16 July 2006</FONT></P>
<P align=center><FONT color=#ff00ff><IMG height=554
src="http://www.500kc.com/N4ICK/500kHz%20Tx_011.jpg" width=645 border=0
NOSEND="1"></FONT><B><FONT color=#0000ff size=+1></FONT></B></P>
<P align=left><FONT face="Arial "><FONT color=#000000>The output of a standard
"can" Xtal oscillator at 5,068 kHz is fed to a 7490 divide-by-10 stage. The
resulting 506.8 kHz square wave is fed directly to ½ of the 4427 driver, and
also inverted by ¼ of the 7400 that feeds the other half of the 4427 (Q and not
Q).</FONT><FONT color=#000000></FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>The Q (and not Q)
square-wave is first DC-restored by the 1N5819 Schottky diode and then applied
to the gate of a MTW32N25E power MOSFET. A Zobel network consisting of a 5 Ohm
resistor and a 4.7nF polypropylene capacitor was inserted at the drain to avoid
potential problems.</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>The two power MOSFETS are
parallel-fed via T1, while T2 matches the low output impedance of these MOSFETs
to a 50 Ohm load.</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>Testing was conducted into
a 50 Ohm dummy load.</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>The output waveform is a
reasonable-looking square-wave, 184 volts Peak-to-Peak.</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>Power input : 12 volts DC
at 12 amperes = 144 watts.</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>Power output: 134 watts
square wave (in fact a little less, as the square wave is not
perfect).</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>Efficiency = 134/144 =
93%</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>Theoretical fundamental
content = [4 * 82/p * sin x ] = 104 watts Output power after a two stage
low-pass filter = about 99 watts (to be further optimized).</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>The MTW32N25E MOSFETs have
the following specifications:</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>32 amps; 250
volts; <FONT size=+2>R</FONT>on = 0.07 Ohm; <FONT size=+2>P</FONT>D =
250 watts @ 25°C.;</FONT></FONT></P>
<P align=left><FONT face="Arial "><FONT color=#000000>(This design is based on
several transmitters previously built for operation in the 136 kHz band. See,
for instance, <I>RadCom</I>, February 2003, page 67).</FONT></FONT></P>
<P align=left><FONT face="Arial " color=#000000><I>N4ICK</I></FONT></P>
<HR>
<P align=center><FONT face="Arial " color=#000000><I><IMG height=598
src="http://www.500kc.com/N4ICK/500kHz_driver.jpg" width=800 border=0
NOSEND="1"></I></FONT></P>
<P align=center><FONT face="Arial " color=#000000><I><IMG height=613
src="http://www.500kc.com/N4ICK/500kHz_Tx.jpg" width=800 border=0
NOSEND="1"></I></FONT></P>
<P align=center><FONT face="Arial " color=#000000><I><IMG height=488
src="http://www.500kc.com/N4ICK/500kHz_output.jpg" width=697 border=0
NOSEND="1"></I></FONT></P></SPAN><BR>-- <BR>António Matias
<DIV><BR></DIV>
<DIV>CT1FFU - CR5A </DIV>
<DIV><BR></DIV>
<DIV><A href="http://www.dxpatrol.com"
target=_blank>www.dxpatrol.com</A> </DIV>
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<DIV>QRV: HF, 6m, 4m,2m,70cm,23cm</DIV>
<DIV>SSB, CW, MGM</DIV>
<DIV>DX, EME, Contest,Sat.</DIV>
<DIV><BR></DIV><BR><SPAN class=765583910-23022011><FONT
face="Meta Correios Portugal" color=#0000ff> Fonte: <FONT face=Tahoma
color=#000000 size=2>ct-comunicacoes-e-tecnologias@googlegroups.com <B>Em nome
de </B>Antonio Matias</FONT><BR> </FONT></SPAN></BODY></HTML>