Dummy load

Related wiki pages: Antennas, SWR

Why use a dummy load?

A Dummy Load is used instead of an antenna when a transceiver is tested or adjusted. Reasons for using a dummy load include:

• using a transceiver without a load - either an antenna or a dummy load can seriously damage it

• a transceiver will exhibit different transmitting characteristics with a load, compared to transmitting without one. This can lead to incorrect adjustments being made to the transceiver circuits

• transmitting into a dummy load with a badly aligned transceiver does not cause interference

What are the characteristics of a good dummy load?

The ideal dummy load will:

• be purely resistive, with a resistance equal to the impedance of the feedline or antenna that the transceiver will normally be used with.

• be designed and constructed to absorb the amount of power that the transceiver delivers

• normally have a resistance of either 50<math>\Omega</math> or 75<math>\Omega </math>

Are there different sorts of dummy load?

In a word, yes. Dummy loads are known as either:

• wet - the resistance is immersed in mineral oil to dissipate heat or

• dry - the resistance will generally be integral to a heatsink, often cylindrical in shape

Can I make my own?

Yes. Non-inductive resistors are required so that the dummy load is as close as possible to being resistive only.

Where can I buy non-inductive resistors from?

Look for metal film or metal oxide resistors. For example, twenty 1K<math>\Omega</math> resistors - each rated at 3W or more - mounted in parallel will provide an almost purely resistive load capable of handling 100W+ from a transceiver.

Where can I buy a dummy load?

• RF parts

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