Antenna splitters

Not strictly OpenWrt related but.... I am looking at a system where I need to split an antenna feed between 2 antennas.

Splitters seem to run anywhere from $0.99 from China to $95 from others.

Is it feasible to split an antenna feed between 2 antennas?

Not and gain anything meaningful as far as 802.11 goes. It’s probably a net loss.

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[quote="cptdondo, post:1, topic:37447, full:true"]Is it feasible to split an antenna feed between 2 antennas?

Not sure what you meant by split here. Did you mean to have to antennas connected in parallel and feed them into the antenna port on the device? If so, then I guess you will need to make sure the impedance of the line that connects into the antenna port matches the impedance of the port.

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Yes. Two parallel antennas, one inside and one outside. The application is an ambulance - basically an aluminum box, so to get a signal both inside and outside I need an antenna inside and outside. Trying to figure out if it's doable, and if so, what are the concerns.

In practice, even for advanced home users - no (even most licensed ham operators won't have the necessary measuring equipment for those frequencies).

Two dual-band APs (the cheapest option) or a single tri-band AP with the third radio reserved for the external coverage would be a much easier approach.


Even locating the unit near the windshield may be sufficient. The wavelengths here are 6-12 cm, so the windshield is huge, by comparison. If you’ve got coverage problems out the back, an Ethernet cable to a tiny unit like the GL.iNet AR300M to provide 2.4 GHz coverage on a different channel may do the trick.

Do you already have data on another service to the vehicle or do you need LTE or the like as well?


In an antenna communication, my understanding is the antenna and the port its connected to must have the same impedance for a maximum performance and a minimum lost. If you connect two antennas in parallel, it will give you a total of half impedance and that will probably not a good idea.

I don't know if the following will work or not: Take 4x such an antenna and connect two of them in a series to double its impedance. Now, you will have 2x of 2 antennas connected in series with a double in impedance. Then, connect them in parallel. This will cut down its total impedance in half which is the original impedance of the antenna (of course assuming each of the 4 antennas has identical impedance). Now, connect the antennas to your device and see if that will work. Again, I have never done this and don't know if it will work. If you do this, I sure would like to hear your report.

The connectors and cables alone will kill you with this approach. There are impedance-matching networks available for this, but buying (imported) junk isn't going to get you there.For am example of a "real" splitter/combiner

Add to the US$75 of that unit $5-10 each for professional-grade connectors and a a good chunk more for LMR-240-UF cable or comparable, and $50 for the tooling for the cable and $50-500 for crimp tooling for the connectors.

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Get an external USB adapter with antenna ?

And dont forget that even good low loss cable, (read large and expensive) has a lot of loss at these frequencies. The typical small diameter stuff commonly used is worse. You could lose half your signal or worse on a 5 foot piece, so forget doing 20-30' runs... better to move the radio and use a short run.

Edit: Didnt notice that the pic above wasnt a bad example of ext antenna w too much coax, but an example of what I was suggesting. Just dont plug it into a USB3 to avoid possible 2.4ghz interference!

Another way might be place router inside of vehicle roof and have ext antenna w a short, foot or less length of cable connecting. Then, eth cable to wherever.

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Maximum length of USB 2.0 cable:

USB 2.0 Connectors (Plugs)

The 2.0 specification limits the length of a cable between USB 2.0 devices (Full Speed or Hi-Speed) to 5 meters (or about 16 feet and 5 inches). In other words, you cannot just connect a bunch of extension cables together (like taking a 6 foot cord and extending it with 4 other 6 foot extension cords) and run them 30 feet to another room. However, you can connect a 6 foot cable with a 10 foot extension cable for a total of 16 feet, which is below the maximum cable length for USB 2.0

Can this USB/RJ45 adapter and cat5 cable be used to extend the limit in length?

No, How are you going to provide power to the external outdoor wifi.

If you would like to use Cat5 cable etc, then get a outdoor Access Point (With or Without PoE)

Your main router will need a spare LAN Port to connect the Access Point via LAN Cable.


Something like this would work

You will need to work out a solution for the power source for the PoE injector
Obviously you will use it in AP mode

Is USB over Ethernet supported in openwrt ? How does it work ? Are there any limitation ? We are talking about both USB 2.0 and 3.1

@pippo A different thread for this off-topic question would be more appropriate.

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