Measuring Splitter/combiners

[prcguy]

Hi prcguy, how is the fact that you drive the combiner with two 1mW signals and get out 2mW consistent with your answer that we lose 3db in the combiner?

I'm sure at some time there is some concept where you logically came to the conclusion that combiners have 3db loss. It maybe that when you add two voltages, you get 4 times the power or +6db. so the splitter must have 3db loss to end up with +3db. But a combiner does not add voltages in series, it puts them in parallel after an impedance conversion.

Its not a concept, its how it works. You can see in my pictures a two way combiner has 3dB loss per port, you cannot escape that. So if it has 3dB loss and you get 3dB gain from combining then there is 3dB missing, otherwise two 0dB singals combined would give 0dBm out due to the internal 3dB loss. If you could break the laws of physics and have a zero loss combiner then no explanation would be needed.

All the specs on 2-way splitter/combiners show they have an inherent 3dB loss. I showed you they have 3dB loss in the splitter mode and in the combiner mode. If you can't see the problem of a missing 3dB in the combining process that needs explaining then I can't help you at this point.

 

[prcguy]

At this point I believe we are in the same page with our understanding of power in and power out of splitters and combiners, which is good.

The contention stems from references to combiner internal loss, such as ‘If the combining process only had 3dB gain then I would get 0dBm out of a combiner that I fed 0dBm in both ports due to its internal loss of 3dB per port that would eat up my 3dB gain from combining’. Is internal loss referencing power loss?

If so, then simply tracking power out vs power in of a typical combiner shows there cannot be a ~3dB internal power loss term.

If ‘internal loss’ is not referencing power, then what is it referencing?

Internal loss in a splitter or combiner is power loss measured in dB. Whatever you put into one port over its rated power handling range will come out about 3dB less. Its a constant. I happened to use 0dBm for my testing in this thread but I have combiners here rated to about 150w and they have about 3dB loss. I've used waveguide magic Tees to combine high power microwave, in one case two 3,500 watt Klystron amps to get almost 7,000 watts out. In all cases the two way combiners had about 3dB loss.

Maybe its time to contact someone you trust who teaches RF theory and ask them as I am either failing to get the point across or you just don't want to believe what I'm saying here.

 

[KevinC]

Maybe its time to contact someone you trust who teaches RF theory and ask them as I am either failing to get the point across or you just don't want to believe what I'm saying here.

Good idea as this ain't going nowhere.

@prcguy, thanks for your patience!