DummyLoad 100 Watts
Practical implementation
The required resistance of 50 ohms is achieved by the parallel connection of 54 Metalloxydwiderständen (Figure 1) of the series E12 with 2.7 KOhm [2] and supporting a load of 2 watts. This results in a computational capacity of about 100 watts. The benefit must but without forced cooling with ventilators etc. Apply only for about a minute, otherwise the resistors are too hot. Through the interconnection of resistors inductors are minimized, the load appears purely resistive and the standing wave ratio in the KW area is over 1: 1.1 also not on the 2-m band result 1: 1.5.
Figure 1 shows the size comparison of the resistance for a load of 2 watts, the dimensions – length 12 mm and diameter of 3.6 mm – come very small and allow a compact construction to.
In my sample copy was obtained after the brazing together a resistance of 50.8 ohms, which fell to 49.8 ohms after a burn. Since resistors have a tolerance of 5%, to variations which are by later adding or Auskneifen individual specimens but easily compensated result. The number of resistors can be increased for greater loads, ie for 200 watts one takes about 104 copies a 2 watts with a resistance of 5.2 ohms.
The resistors are inserted through two protoboard (strip breadboard) and soldered. The distance between the two plates resulting from the length of the resistors (12 mm). The connecting wires are pinched off after soldering. A PL-jack is soldered directly to the top board, the center pin is connected to a thick wire as possible with the lower board. Since the individual strips of boards among themselves are not connected, bridges to at least 3 points with 1mm wire create.
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radiation reduction
If you have managed to assemble without problems, then you can worry to reduce the emission of the terminating resistor. For this purpose, is the installation of an in-hf-proof metal housing. When inspecting the kitchen I noticed a cubical caddy (Figure 4), the. With an edge length of 9 cm and a circular opening of 8 cm, which had the right dimensions
The installation brought a reduction in the emission by 25 dB, measured with a second receiver in about 10 meters, and was worth it. A further reduction of radiation by about 10 dB resulted slightly by omitting the coaxial cable between TX and dummy load and provisions for alternative power on a standing wave barrier of Ferroxcube ferrite cores, such as those offered in either ready-made, or delivered from there toroids self can be produced. Twenty toroids type Ferroxcube CST9.5 / 5.1 / 15-3S4 be pushed on a ca 40 cm long RG58U, the cable is fitted with plugs / sockets, finished. The sheath wave barriers or even 1: 1 called BALUN, distinguish themselves also in the adaptation of end-fed antennas and were first described by W2DU.
