FlightAware Discussions

Cable + Antenna + Pi

Hi All,

I live in Vermont, about 30ish miles from the boarder, which is not exactly prime-time traffic for flights, unlike say JFK. Looking to setup the USB pro stick (my app for the official hardware denied). In any event i think with a roof-mounted option, I will be abe to see BTV, PLB, KFSO traffic. Maybe bit father, but we shall see.

For my setup, i am looking to do a PiAware + NTP/GPSD setup, to also get NTP for my network. So I am looking at a chimney mount option with maybe a 3-foot pole. My plan would be to run the wires down the chimney and inside the basement. FYI the chimney is abandoned, was used for oil furnace but we went with propane which is a whole different setup.

I estimate maybe 25Feet of cable should do the trick. What kind of signal loss should I expect from this? I have debated simply putting the Pi in a weatherproof enclosure with a poe hat, but vermont gets both hot and cot here. Not looking for a new pi every year kind of thing.

Depends on the coax you use.
This coax is perfectly fine for ADS-B / 1090 MHz: https://www.amazon.com/gp/product/B00QZEQ5EA

The longer length for this listing go from LMR240 up to LMR400 which has lower loss per length.
But LMR240 is just fine for 25 ft.
You can get away with lesser coax, this is premium stuff.
Just look up a data sheet and check the attenuation for 1090 MHz.

I don’t really see the reason for a GPSD but that’s just me.
What GPS needs in regards to coax or whatever, i have no clue.

25 feet with a good cable should not have that much loss. You could use an additional LNA which will be between cable and the USB stick you select.

I also do not see a reason for GPSD. There is no real value for it. NTP can be obtained from the Internet, no need to use additional sources for it.
I am operating as a second receiver an AirSquitter from Jetvision. This device is GPS equipped which gives the exact position and time. But that’s all what it is used for. For a fully operational MLAT you can setup your exact location manually.

Do you have already a usable GPS-Antenna for your plan?

I do not have a selected antenna for the gps. But my purpose for wanting GPS is because i restrict IOT devices and security cameras from direct internet access. So this means i need a device on the network to do NTP, which is just serving as a STRUM-2/3 at that point. So for like $100 more, i can simply get a stratum-1 server and cut out the middle-man.

My thought of dual purposing this PI is simply efficiency, and limit the device exposure to lightening strikes.

Any good router should be capable to request NTP time and work as an NTP server for all your local devices.

At least my Router (AVM FritzBox) is capabable to do so.
But i understand your purpose of efficiency. You could also think about a cheap Raspberry Zero doing the job instead of the Flightfeeder. That will give you more flexibility

Lightning in this exposed position needs to be considered for sure

It’s really not critical.
Even Trimble only recommend RG6 for their GPSDO.
To keep jitter to a minimum, a GPS antenna need to have a small phase-centre. This requires the antenna it’s self to be small so in turn it needs a high gain LNA mounted at the antenna (25dB is typical, mine is 40dB (my Trimble Thunderbolt is a bit deaf)).

With so much gain at the antenna, you can put up with significant loss in the feeder.

Ah didn’t know it’s active antennas but i was somewhat suspecting that as GPS is a pretty weak signal :slight_smile:

@foxhunter I’d once again urge to read. And maybe google what stratum means in reference to NTP.

2 Likes

I did not read that part properly