Actually Steve, the idea is pretty simple. When using a class C final amplifier the output RF voltage is directly proportional to the plate to cathode voltage. Most of the time the cathode is grounded so we just say "plate voltage" or "plate modulation". This means that if the plate voltage is doubled then the RF output voltage will also double. It's sort of like saying that if we raise the voltage to a lamp it will put out more light, etc. Power or "Wattage" is generally measured or expressed in average values unless otherwise stated. The is the difference from a horse pulling continuously on a wagon there by exerting a max of one horsepower, verses jerking periodically on it. A lamp will put out the same amount of light will 110 volts DC as it would with 110 volts AC from the wall power. The wall power is measured in RMS (root mean square) value. The peak voltage of the AC wave is ((sqrt of 2) * 110 volts) or (about 1.414 * 110). The RMS voltage value of the wave is (sqrt of .5 * peak) or ( about .707 * peak). To modulate a class C rig to 100% (pos and neg) requires the peak voltage to be equal that of the DC supply so the average audio power required is half the DC power to the plate. For more on this see http://www.qsl.net/wa5bxo/asyam/aam3.html .
I'm glad to see questions of this nature. John, WA5BXO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Sunday, October 10, 2004 7:12 AM To: [email protected] Subject: [AMRadio] Mod xmfr? Hi all: I need to better understand the workings of a plate modulator for AM. Considering the RF amp with 2 x 813's and the modulator with 2 x 813's - what are the equations and math to work out the required wattage, impedance, step ratio etc. And, just how much can one depart from the ideal arrangement and with what effects? ( should I not be able to find the right xmfr for this amp I'm planning to build ). PS: I am seeking that modulator xmfr at this time. Tnx, Steve WA2TAK ______________________________________________________________ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected]
