‰  NOW 35 WPM  ‰  TEXT IS FROM DECEMBER 2008 QST  PAGES 62, 63 AND 75  ‰

EXPERIMENT 71 CIRCUIT LAYOUT  SUCCESS WITH RADIO ELECTRONICS HAS A LOT TO
DO WITH KNOWING HOW TO CONSTRUCT A CIRCUIT.  AS FREQUENCY INCREASES, THIS
SORT OF RADIO KNOW HOW BECOMES INCREASINGLY IMPORTANT.  THIS MONTHS
EXPERIMENT WILL PRESENT AN EXAMPLE OF THE EFFECTS OF CIRCUIT LAYOUT ON ITS
PERFORMANCE AT DIFFERENT FREQUENCIES.  THIS EXPERIMENT IS BASED ON A COLUMN
BY DAVE KELLEY, ND3K, PROFESSOR OF ELECTRICAL ENGINEERING AT BUCKNELL
UNIVERSITY AND A FREQUENT READER OF HANDS ON RADIO.  THE BASIC FILTER THE
CIRCUIT WERE GOING TO BUILD IN THREE DIFFERENT WAYS IS A LOW PASS FILTER
WITH A CUTOFF FREQUENCY OF AROUND 28 MHZ.  THE SCHEMATIC IS SHOWN IN FIGURE
1.  THE FILTER IS DESIGNED TO BE USED WITH A 50 O SOURCE AND LOAD.  FIGURE
1 ALSO SHOWS IN RED THE PARASITIC REACTANCES ASSOCIATED WITH EACH OF THE
IDEAL COMPONENTS.  FOR EXAMPLE, THE INTERTURN CAPACITANCE OF L1 CREATES
CW1, TYPICALLY A FEW PF FOR AN AIRWOUND COIL OF THE SIZE YOULL WIND.  THE
LEAD INDUCTANCE OF C1 APPEARS AS LS1 AND IS ABOUT 12 NH/INCH FOR 20 GAUGE
WIRE.  MORE PARASITIC CAPACITANCE APPEARS AS CIO, THE CAPACITANCE BETWEEN
THE INPUT AND OUTPUT CONNECTIONS.  THE SIZE AND PLACEMENT OF THE COMPONENTS
‰  FROM PAGE 75  ‰
2 43 1,798 OH New Bern ARC W4EWN K4DJW 251 2 12 1,764 NC Jones Co ARC W0CWP
452 2 10 1,754 IA Ellijhay ARS NB8N 296 2 40 1,746 GA ARC of Savannah W4HBB
405 2 27 1,744 GA PJ’ s Group / WAFAR W9FT 441 2 18 1,732 IL Skyline Tower
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ