Dummy load: Difference between revisions
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* normally have a resistance of either 50<math>\Omega</math> or 75<math>\Omega </math> | * normally have a resistance of either 50<math>\Omega</math> or 75<math>\Omega </math> | ||
==Are there different sorts of dummy load? | ==Are there different sorts of dummy load?== | ||
In a word, yes. Dummy loads are known as either: | In a word, yes. Dummy loads are known as either: | ||
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* dry - the resistance will generally be integral to a heatsink, often cylindrical in shape | * 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. | 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? | ==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. | 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. | ||
Revision as of 00:52, 24 August 2008
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.