This is a easy dummy load; I used common 2W/470 ohm resistor in parallel, obtaining 52 ohm/18 watt;
you must know that if you want a precise dummy load for high frequency you need a no-inductive resistor (those in the picture have high precision until VHF, I never tried up, see Picture 1), because the common resistor, going up with frequency, have more and more high inductive value;
but you can useful use the common resistors if:

1. you stop at 28 MHZ (I never have tried 50 MHZ but sure it's no good on 144 MHZ);
2. don't pretend to have an "high precision" tool;

I'll explain better with an example: I put my "precise" dummy load (with no-inductive resistor) back my RTX and have measure S.W.R.; it was 1:1,1 from 1.8 MHZ to 144; I removed it and have used this new one: I have S.W.R. 1:1,1 at 1,8 MHZ and 1:1,2 at 28 MHZ, but at 144 MHz IT'S 1:2.
In HF band you can use it (a S.W.R. 1:1,2 is OK) for all uses (testing coaxial cables, tune antennas, linear amplifier ecc.); but you can not use it on VHF.

Common resistor have an inductive value when you go up with frequency; but we also know that:

1. making a parallel of inductance you can make the inductance value lower;
2. if you put a capacitor in parallel to an inductance you can eliminate the inductance.

From 1) cames that we can use common resitor making a parallel; so doing we obtain an higher power dissipation; in my one I have obtained 18 watt: putting the resistors in a liquid (oil in my one) we make this value higher; in my dummy load I usually put 100 watt for medium-short time with no problem.
About oil to use I think the transformer one is the best (I put used oil caming from my moto HI).

From 2) cames that we can use common resistor on high frequency adding a capacitance: if we put around a common resistor a small copper sheet, a metallic sheet (the dummy load box) or two metallic plate ecc. we obtain a capacitor that let we use this dummy load on the high frequency (be careful; dont' exceed with capacitance).

Let's see now how I build it: as box I used a metallic one used for containing paint (see pictire 2); put the SO239 (with the dummy load soldered) on the top (on a metallic plate) and then put the box and the plate together using 4 screw bolt (3mm)(see picture 3).
I pour the oil in the box trough a small hole (closed with an screw bolt) (make sure the oil cover all the resistors).
The resistors are soldered on two copper plate (the same you use for printed board) trough 9(x2) holes: in this way you have a small capacitor to make the inductance value lower.

You can build also dummy load for 75 ohm or other values for various tests.

These are the Resistive (R) and Reactive (X) value measured with my MFJ259B in the range  0-170MHZ relative to my home-made dummy load

 Freq. R (ohm) X (ohm) 0 (DC) 51 - 1 51 0 2 51 0 3 51 0 4 51 0 5 51 0 6 51 0 7 51 0 8 51 0 9 51 0 10 51 0 11 51 0 12 51 1 13 51 1 14 51 2 15 51 2 16 51 2 17 51 3 18 51 3 19 51 3 20 51 3 21 51 4 22 52 4 23 52 5 24 52 5 25 52 5 26 52 5 27 52 6 28 52 6 29 52 7 30 53 7 35 54 7 40 55 9 45 55 9 50 60 8 55 61 10 60 63 10 65 65 10 70 66 7 75 68 13 80 71 14 85 74 13 90 79 10 95 81 10 100 88 0 110 95 0 120 97 0 130 101 6 140 101 30 150 96 35 160 95 40 170 97 40

The following are value of my 1Kw  dummy load using a single 300W anti-inductive resistor (by MFJ)

 Freq. R (ohm) X (ohm) 0 (DC) 59 - 1 59 0 2 59 0 3 59 0 4 59 0 5 59 0 6 59 0 7 59 0 8 59 0 9 59 0 10 59 0 11 59 0 12 59 0 13 59 0 14 59 0 15 59 0 16 59 0 17 59 0 18 59 0 19 59 0 20 59 0 21 59 0 22 59 0 23 59 0 24 59 0 25 60 0 26 60 0 27 60 0 28 60 0 29 60 0 30 60 0 35 61 0 40 61 0 45 61 0 50 62 0 55 63 0 60 63 0 65 64 0 70 64 4 75 65 5 80 66 4 85 67 6 90 66 9 95 69 9 100 68 13 110 68 16 120 65 22 130 64 26 140 61 29 150 61 31 160 58 37 170 61 43

The following are value of a dummy load made with a single "wire power resistor"

 Freq. R (ohm) X (ohm) 0 (DC) 56 - 1 56 0 2 56 0 3 56 0 4 56 0 5 56 0 6 56 0 7 56 2 8 56 4 9 56 5 10 56 5 11 57 6 12 57 7 13 58 8 14 58 9 15 59 9 16 59 10 17 59 12 18 60 12 19 61 13 20 61 13 21 62 14 22 63 15 23 64 15 24 65 16 25 65 16 26 66 17 27 67 17 28 68 18 29 68 20 30 70 21 35 83 14 40 86 18 45 91 23 50 108 0 55 117 0 60 124 0 65 131 0 70 128 6 75 129 54 80 108 78 85 95 83 90 80 87 95 55 94 100 45 80 110 31 70 120 25 56 130 19 48 140 13 42 150 10 36 160 9 29 170 8 24

73 de iz7ath, Talino Tribuzio