Max co-ax length


I need to install longer than 15 meters of co-ax cable to connect my FF to its antenna. What is the max I can go to? Also, can I install c80 meters of co-ax cable to optimally position my antenna?


For 80m you’ll need some pretty special low-loss co-ax to get any signal at the receiver end, LMR-400 or better.

Describe your site - lets see if we can come up with an alternative workable configuration (for example Cat 5 network cables are good to 100m, if the the receiver could be placed nearer the antenna)


Thanks Peter,
Well I am planning to mount the antenna at the top of the building, and the top is at least 4 stories above me. Longer Cat 5 would only take me to the end of the room till the window and then the coax needs to run from inside the window till the antenna mount 4 stories above. I do not want to put the receiver anywhere outside for a multitude of reasons, however, it can happily sit by the window. I’ve the coax that came with the FF but that isnt long enough. Can that we made longer using connectors?


LMR-400 is wonderful stuff. I use it a lot. It’s the same diameter as RG-8 (0.405 inches, around 10mm), has a solid core so it is NOT very flexible, and takes special connectors if you want to do things right. At 1GHz, 100 meters gives you around 12dB signal loss. It’s around $1 per foot in long runs (not including connectors).

LMR-400 is not invisible; it’s not quite as bad as running a garden hose up the side of a building, but it is not inconspicuous (LDF4-50A is the garden hose). It also has to be installed correctly – no sharp radius bends, don’t scrape the jacket, mountings that allow for expansion and contraction, the whole thing. If you expect it to last through a year, it needs to be a solid installation, which would seem to involve building management, approval at least, and assistance at best.

Let’s hear about your plans "B,’ “C,” and “D.”

I’d hope one of them involves putting the receiver closer to the roof and running an Ethernet connection from there, or even WiFi. Or installing stations on the three other sides of the building and combining the output; might be cheaper.

–bob k6rtm


Well - actually, my plan b is to explore putting up multiole sites or multiple antennas - is it possible to link multiple antennas to one FF?


Combining signals from multiple antennas is a really difficult problem and you do not want to go there. Combining the outputs of multiple Pis into one PiAware feed is really easy and only requires network connectivity among the Pis.

Lots of people do this; I run a number of different Pis trying different variations on antennas, filtering, and the like. One Pi gets the combined feeds and sends that on.

bob k6rtm


Hi Bob,
Thank you for that suggestion - can you guide me to any resources to set this kind of architecture? As I mentioned, I am running one FF currently. This option has become very lucrative given that the FF boxes will support Wi-FI.

Sorry if these are very rudimentary questions.


Is there a utility riser duct etc where you can put cables (building owners allowing) to equipment near the roof? Anything done here would need to be done to code using fire resistant cables and installation to a tidy professional standard.

Bringing the radio signal down the building might be possible but it would be much simpler to put the receiver near the roof. The issues then are protecting the equipment, powering the equipment and getting the received data out

Are we talking about a FlightAware supplied flight feeder (quite an expensive box), or something simpler like a “Raspberry Pi” based receiver - where the equipment cost is probably well under $100 for everything? (protective enclosures to suit the receiver location and commercial antennas would add to that cost).

If you don’t have power near the roof, then the simplest answer might be Cat5 to the roof, put the receiver in a box up there. Standard CAT5 cable has four pairs of conductors, two are used by Ethernet - the other two pairs are often used to power equipment at the remote end of the cable.


Oops – I’m guilty of not reading for content… I assumed you were running a Raspberry Pi with dump1090 and PiAware – for that configuration, feeding data from multiple dump1090 instances to a dump1090 hub and PiAware instance is easy. If you’re running an FF box, I have no clue what goes on inside that box.

For the Raspberry Pi - dump1090 - PiAware configuration, you use a simple script with netcat to periodically send data from the slaves to the hub.




my coax run to the roof of my office building is about 40 feet into the dongle, and then a powered 30’ usb extender to my pi. my coverage is so-so on a 14 element coaxcolinear.