‰  NOW 40 WPM  ‰  TEXT IS FROM DECEMBER 2008 QST  PAGES 62, 63 AND 75  ‰

SOURCE BY SOLDERING THE COAX CENTER CONDUCTOR AND SHIELD DIRECTLY TO THE
INPUT TERMINALS.  USE THE SPREADSHEET TO GRAPH THE CIRCUITS FREQUENCY
RESPONSE.  COMPARED TO THE FREQUENCY RESPONSE OF THE BREADBOARD FILTER, THE
TERMINAL STRIP VERSION WILL SHOW A MUCH 
‰  FROM PAGE 75  ‰
City Repeater Club K1DFS K1WMS 303 2 8 1,586 CT Camden Co ARS K4B 258 2 15

AFFECTS EACH OF THESE PARASITIC VALUES.  SANS SOLDER THE FIRST VERSION OF
THE CIRCUIT IS BUILT ON A SOLDERLESS BREADBOARD, AS SEEN IN FIGURE 2.  TO
WIND THE INDUCTORS, START WITH 16 INCHES OF SOLID 20 GAUGE WIRE.  SCRAPE
THE ENAMEL COATING OFF THE ENDS OF THE WIRE WITH A KNIFE OR FILE.  ON A 1/2
INCH FORM SUCH AS A DRILL BIT OR DOWEL, WIND NINE TURNS OVER A LENGTH OF
ABOUT 7/8 INCH.  LEAVE ABOUT 3/4 INCH OF WIRE ON EACH END TO MAKE LEADS.
PLUG THE INDUCTORS INTO THE BREADBOARD AT AN ANGLE TO EACH OTHER.  IF THE
INDUCTORS ARE PLACED END TO END IN A STRAIGHT LINE, THEIR MAGNETIC FIELDS
WILL COUPLE AND UPSET CIRCUIT PERFORMANCE QUITE A BIT.  CONNECT THE
CAPACITORS FROM THE INDUCTORS TO THE BREADBOARDS GROUND RAIL.  ITS NOT
NECESSARY TO MINIMIZE LEAD LENGTH OR ARRANGEMENT YET.  NOW COMES THE FUN
PART MEASURING HOW THE CIRCUIT RESPONDS AT DIFFERENT FREQUENCIES.  AS A
SIGNAL SOURCE, YOULL NEED A SIGNAL GENERATOR OR AN SWR ANALYZER, SUCH AS AN
MFJ 259.  ANY STABLE SOURCE THAT CAN OUTPUT MORE THAN A FEW HUNDRED
‰  FROM PAGE 75  ‰
ARC W7DTV 663 2 15 1,692 OR Cape May Co. ARC N2CMC W2CMC 194 2 18 1,686 SNJ
Buffalo AR Repeater Assn W2EUP 463 2 27 1,666 WNY MM ARC W8PIF 682 1 44

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 40 WPM TEXT  ‰  QST DE W1AW  ƒ