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KG6BAJ > ANTENA 22.06.08 10:50l 39 Lines 1843 Bytes #999 (0) @ NWSGRP
BID : 941_GVCITY
Read: GUEST
Subj: Chapter 19A from "Reflections III" - Step 1 response
Path: ON0AR<I0TVL<CX2SA<KD4KVG<KG4IVD<W4RAL<KD4GCA<KG6BAJ<KG6BAJ
Sent: 080621/1515Z @:KG6BAJ.#nca.ca.usa.noam #:941 [Grass Valley] InterGate $:9
** NEWSGROUP: rec.radio.amateur.antenna
** FROM : Richard Clark <kb7qhc@comcast.net>
Step 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.
There are several points in response here:
1.The load specification ( 50 + j0-ohm) is for full output power, not
some portion of it. This is a minor point.
2.Maximum power from a TS-830S can be as high as 120W, could be lower
depending on finals' service life. This is a minor point.
3.Rated typical Plate Current for the 6146B is 220mA. Running more at
higher voltage (typical is 750V) to obtain less power sounds like the
amp is being strained to produce 100W.
4.“Available Powerö is 208W. Efficiency and other considerations
certainly lower this, but it would appear that efficiency has been
red-lined at 48% by this step's assertions. The red-line at 48%
efficiency may reveal the aforementioned strain.
73's
Richard Clark, KB7QHC
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