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Ham radio antenna combiners or diplexers are a useful item in many amateur radio stations.
Antenna diplexers or combiners combine the signals from two sources on different frequencies and allow them to travel along a single feeder.
One typical example of an amateur radio antenna diplexer use would be where an all band HF and VHF / UHF rig is used and a single output is available. An antenna duplexer can be used to divert the signal to the right antenna - possibly using an HF antenna for bands up to 30 MHz and then a multi band VHF / UHF antenna for bands able 30 MHz.
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It is worth noting that the term duplexer is often seen being used to describe diplexers. A duplexer is a module that allows simultaneous transmission of signals in both directions at the same time, i.e. allowing duplex operation.
What to look for when buying a diplexer
When selecting a diplexer or antenna combiner (duplexer) to buy it is necessary to understand how diplexers work.
The basis around which they operate is that they split or combine signals - signals above one frequency are routed to one output, and signals below this frequency are routed to the other.
It is worth noting that antenna diplexers or combiners can be used in both directions - in other words for splitting or combining signals.
There are several key aspects to look for int he specification when buying an antenna duplexer for amateur radio or any other use.
- Frequency bands: Check that the duplexer / splitter / combiner has the required frequency split. For example, if all he HF bands are to be routed to an HF antenna and then all the VHF bands to a VHF antenna, then it should be labelled such that one output is for frequencies up to 30 MHz, and then the other for frequencies above 50 MHz, etc.
- Insertion loss: All splitters / combiners / diplexers will introduce some loss, so this needs to be checked before buying the splitter / combiner / diplexer. This may typically be around 0.2 dB or a little more. Check that it does not introduce too much loss when compared to the required performance for the overall station.
- Power handling: Another important parameter to check before buying, is the power handling capability. The amateur radio combiner / duplexer should be able to handle more than the anticipated output power from the transceiver being used. If the diplexer is only to be used for receiving, then this should not be an issue.
- VSWR: There is bound to be some mismatch caused by the ham radio antenna combiner / diplexer. This should typically be below about 1.2:1.
- Impedance: Virtually all professional and amateur radio RF feeders are 50Ω, but on occasions there may be some use of other impedances. Before buying, check the impedance of the combiner is what is needed, typically 50Ω.
When selecting an antenna combiner to buy, it is worth checking all the available sources. Even though the correct terminology is diplexer, or splitter / combiner, they are often referred to as ham radio antenna duplexers, even though, this is really the wrong terminology.