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1.7 Splitter
An antenna splitter or signal splitter is a device that splits a signal from one input to multiple outputs. It can be used to connect one antenna to multiple receivers.
Splitters come with one input and multiple outputs
Usual splitters are:
- 1 in / 2 out
- 1 in / 3 out
- 1 in / 4 out
- 1 in / 8 out
While different types of connectors are available like F or N-type we do strongly recommend SMA connectors as the SDRs and most filter are equipped with those and we try to avoid adapters to keep as much of the signal as possible.
When tracking radiosondes only one concurrent radiosonde can be tracked per SDR, so we have to use multiple SDRs to track multiple sondes.
While it is definitely possible to install one antenna per stick this quickly gets expensive and may not be possible depending on the mounting location.
The antenna splitter allows us to connect multiple SDRs to one antenna.
When using a dualband antenna for 70cm (Radiosondes) and 2m (AIS), it is possible to receive ships and sondes with the same antenna.
There are things to keep in mind when using an antenna splitter:
- Every splitter decreases the signal strength, so it is a good idea to connect an LNA to its input to boost the signal
- Each output port of the splitter needs to either be connected to an SDR or terminated with an 50 Ohm resistor
- Every splitter has a working range, usually 5-1000Mhz or 500-3000Mhz. Make sure that our desired frequencies are well in this range
- AIS is in the 160-162Mhz range
- Radiosondes are in the 400-406Mhz range
- Sadly there are many splitters on the market that do not perform as advertised, so be sure to buy from a good seller and check the splitter with something like a nanoVNA
When using a splitter you can connect your filter to the input or the output of the splitter - but what is the right thing to do?
When using a bandstop filter like a FM bandstop that filters out a specific frequency range you connect that one to the splitter input and all your outputs will receive a filtered signal.
When using a bandpass filter that filters everything but a specific frequency it depends on your setup.
When all your outputs work on the same frequency like 4 times Radiosondes on a 4 times splitter you can connect one bandpass for ~403 MHz on the splitters input and all receivers will receive a filtered signal.
If however you use SDRs on different frequencies like 1x AIS and 3x Radiosonde you can not install a bandpass on the input of the splitter, but you can install bandpasses for the according frequencies on the outputs of the splitter.
TODO