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#11
June 14th 10, 01:23 PM
posted to rec.radio.amateur.antenna
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what happens to reflected energy ?
On 13 jun, 23:43, walt wrote:
On Jun 13, 5:08*pm, Wimpie wrote: On 9 jun, 02:07, Richard Clark wrote: On Tue, 8 Jun 2010 12:17:37 -0700 (PDT), Wimpie wrote: When we go back to my first posting in this thread (the first reply) where I stated that amplifiers do not show 50 Ohms in general, is not that strange and doesn't violate Walt's conclusions. Hi Wimpie, Time to rewind: On Thu, 27 May 2010 19:32:40 -0700 (PDT), walt wrote: The source resistance data reported in Secs 19.8 and 19.9 were obtained using the load variation method with resistive loads. Note that of the six measurements of output source resistance reported in Table 19.1, the average value of the resistance is 50.3 ohms obtained with the reference load resistance of 51.2 ohms, exhibiting an error of only 1.8 percent. Considering these two explicit initial conditions and findings: 1. Using a Kenwood TS-830S transceiver as the RF source, the tuning and loading of the pi-network are adjusted to deliver all the available power into a 50 + j0-ohm load with the grid drive adjusted to deliver the maximum of 100 watts at 4 MHz, thus establishing the area of the RF power window at the input of the pi-network, resistance RLP at the plate, and the slope of the load line. The output source resistance of the amplifier in this condition will later be shown to be 50 ohms. In this condition the DC plate voltage is 800 v and plate current is 260 ma. DC input power is therefore 800 v ? 0.26 a = 208 w. Readings on the Bird 43 wattmeter indicate 100 watts forward and zero watts reflected. (100 watts is the maximum RF output power available at this drive level.) From here on the grid drive is left undisturbed, and the pi-network controls are left undisturbed until Step 10. 2. The amplifier is now powered down and the load resistance RL is measured across the input terminals of the resonant pi-network tank circuit (from plate to ground) with an HP-4815 Vector Impedance Meter. |
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