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$$\Omega$$ or 75$$\Omega $$

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$$\Omega$$ 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