FlightAware Discussions

3-4 pi's connected to one outdoor antenna

I am currently running 3 pi’s hooked up to 3 FA antennas. Is there any way I could use one FA antenna with a splitter of some sort and feed to all three units? If so what gear do I need? Many Thanks.

Sure, just find a splitter with the connectors you need.
Would recommend putting an LNA before the splitter as you obviously have less signal at each out port.

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Take a look at the Mini-Circuits brand of splitters. They are not cheap ($70 MSRP), but they are built incredibly solid and have low loss and high isolation characteristics. Splitters suitable for ADS-B are offered with Type N and SMA connectors. I have 1 into 2 and 1 into 4 splitters. If you get a 4-way for one antenna to drive 3 receivers, make sure you put a termination resistor on the empty port - don’t leave it open. I agree with wesjamis about inserting an LNA somewhere in the chain. Pay special attention to the frequency range of the splitter. A good match for ADS-B would be their 0.5 to 2.0 GHz models. An example is the Mini-Circuits ZAPD-21 for SMA. Both new and used are generally available from multiple vendors on eBay.


Thanks. I am using a Uputronics LNA/Filter on each of them so hopefully those should do.

Thanks for the assist. I found a few listed up on Ebay.

It is possible to use one receiver for everything if use Modes2Mixer2.

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It’s better to use just one amp before the splitter than one for each receiver after the split.
Amplifying after splitting has a worse noise figure, giving worse system performance.
See : https://ava.upuaut.net/?p=836
Using an amp after the splitter would be similar to the third example (9m coax, amp, 1m coax), but probably worse; depends on your exact setup.

I realise that performance with inexpensive dongles is debatable, (ADSB is fairly strong signals, how much external NF affects cheap dongle performance, MDS of cheap dongles, etc) but good engineering is good engineering. Why would you purposely compromise your system when you already have the gear to do it right?

(Don’t know how Cowboy plans to set this up, this is just general use, for reference info)


Be aware the ZAPD-21 will pass DC on all ports.
As the Uptronics amp can be powered by either Bias-T or USB port, it’ll probably put volts down the coax that the dongles won’t appreciate.
If you power the amp with a Bias-T, that dongle will be protected, but the other won’t.

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Pretty sure that it doesn’t output voltage on the coax if you power it via USB.


If you already have FA Pro+ sticks, it’s not out of the question to have an LNA before the split and still keep using LNAs after the split because of the SDRs you still have.

That noise figure shouldn’t be too bad, just turn the gain down to about 20 or something i’d estimate.
By reducing gain and going via the builtin LNA, might only be shifting that gain anyhow so … that’s why i’m saying it might not be worse noise figure compared to an SDR without LNA.

I just found a pic of the PCB. Looks like it is fitted with blocking diodes to prevent exactly what I described.


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I am powering the Uptronics from a external power source using a USB cable and they will be located before the splitter. Is this good enough?. Thanks for all the responses. You guys are the best.

Yes. It looks like my concern was unfounded.
(By good design on the part of Uptronics)