ARLA/CLUSTER: Emissor 100W para 600m, 500kHz
João Gonçalves Costa
joao.a.costa ctt.pt
Quarta-Feira, 23 de Fevereiro de 2011 - 10:40:59 WET
A 100 Watt CW Transmitter for the 500 kHz Band
André Kesteloot N4ICK
16 July 2006
[http://www.500kc.com/N4ICK/500kHz%20Tx_011.jpg]
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).
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.
The two power MOSFETS are parallel-fed via T1, while T2 matches the low output impedance of these MOSFETs to a 50 Ohm load.
Testing was conducted into a 50 Ohm dummy load.
The output waveform is a reasonable-looking square-wave, 184 volts Peak-to-Peak.
Power input : 12 volts DC at 12 amperes = 144 watts.
Power output: 134 watts square wave (in fact a little less, as the square wave is not perfect).
Efficiency = 134/144 = 93%
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).
The MTW32N25E MOSFETs have the following specifications:
32 amps; 250 volts; Ron = 0.07 Ohm; PD = 250 watts @ 25°C.;
(This design is based on several transmitters previously built for operation in the 136 kHz band. See, for instance, RadCom, February 2003, page 67).
N4ICK
________________________________
[http://www.500kc.com/N4ICK/500kHz_driver.jpg]
[http://www.500kc.com/N4ICK/500kHz_Tx.jpg]
[http://www.500kc.com/N4ICK/500kHz_output.jpg]
--
António Matias
CT1FFU - CR5A
www.dxpatrol.com<http://www.dxpatrol.com>
QRV: HF, 6m, 4m,2m,70cm,23cm
SSB, CW, MGM
DX, EME, Contest,Sat.
Fonte: ct-comunicacoes-e-tecnologias googlegroups.com Em nome de Antonio Matias
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