There are times when we may wish to test our transmitter without radiating any significant signal. For this, we would usually substitute the antenna with a dummy load.
A dummy load is an idealised artificial antenna. It is usually screened to prevent radiation. It is basically a resistor capable of absorbing the full power of the transmitter, the value of the resistor will match the output impedance of our transmitter.. Being purely resistive, it presents a perfect match over a very wide frequency range, i.e. SWR is 1:1.
A
dummy load is simple to construct and makes an ideal project for those wishing
to try home construction for the first time. The dummy load in the picture on
the left handles about 50W. It was constructed in about two hours, for around
five pounds. It is shown with its screening cover (a paint can) removed.
The
picture on the right shows a small commercial dummy load handling about 15W, and
costing about twenty-five pounds.
