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G0TSU > TECH 07.01.06 21:05l 47 Lines 1452 Bytes #999 (0) @ WW
BID : 28146_GB7WSX
Read: OE5RCO OE7HNT DL1LCA GUEST OE7FMI
Subj: DummyLoad
Path: DB0FHN<DB0THA<DB0ERF<DB0FBB<DB0IUZ<DB0GOS<DB0RES<ON0BEL<GB7CIP<GB7WSX
Sent: 060107/0240Z 28146@GB7WSX.#32.GBR.EU [Crawley] FBB $:28146_GB7WSX
From: G0TSU@GB7WSX.#32.GBR.EU
To : TECH@WW
Greetings all!
Reading through an archived copy of G8MNY's dummy load article,
I thought I'd share some of the fun I'd had, with one type.
The humble 2 Watt metal film parallel resistor network.
(Wirewound types are no good for RF)
Easy and cheap to obtain, quickly designed and assembled.
It all revolves around the equation 1/ (1/r1) + (1/r2) + (1/r3) etc...
Simple enough to write down, but what if you had 20,000 resistors?
BASIC script (should also work in QBASIC)
10 CLS: CLEAR: PRINT
20 PRINT " Resisitors in parallel by G0TSU "
30 PRINT :PRINT
40 INPUT " Resistor value in Ohm";v
50 PRINT: INPUT " Number of resistors ";n
60 a=1/v : b=a*n : c =1/b
70 PRINT: PRINT " Load =";c;"Ohm"
80 PRINT:PRINT:PRINT " agAin or eXit...
90 IF INKEY$="a" OR INKEY$="A" THEN GOTO 10
100 IF INKEY$="x" OR INKEY$="X" THEN END
110 GOTO 90
Standard resistor values for example:-
10 x 500 Ohm = 50 Ohm = 20W
94 x 4k7 Ohm = 50 Ohm = 188W
112 x 5k6 Ohm = 50 Ohm = 224W
20k x 1M Ohm = 50 Ohm = 40kW
The easiest way to connect them up is using two
strips of veroboard, a few inches of coax and connector.
Solder one end of all the resistors to one and sandwich them
with the other board and solder all those ends together.
The coax braid goes to one board and the centre to the other.
I've heard that dry sand is good as a heat conductor,
maybe someone could build a 40kW load and confirm this?
73! Dem
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