FlightAware Discussions

Weird drop of traffic and range

Hi mates,

I am having a PI 3b+ setup running for 1 year now, with LMR195 cable (6meters) and FA antenna outside on a mast and few converters from N connector to SMA
Stick is FA blue, gain is 49

After updating to Piaware 5 (not sure this was the problem) traffic dropped from 250+ Nm to maxim 100. There is airfcraft traffic, i’ve checked other installations.

I had a lot of rain lately (raining since 1 week now) and i went and brought down the antenna, removed connectors , blew them with a hair dryer and let them sit for 1-2 hours .

Antenna was also having some pressure noise like when you open e pepsi can but not fully so you can hear some hissing.

I also left the antenna on the house heater near my window, put all back together but still no joy

Things done:

  • check the cable for shorts with multimeter, all good
  • used a different dongle
  • used a different power supply for PI (both tester and original are original PI power supplies)
  • installed Piaware from scratch with SD card image, still nothing

The only thing remaining is to use a different PI but i only have a RPI 2 which is very old
This PI is also running with no errors or problems, it has a cooling sink from Pimoroni , temp never went higher than 45 degrees C.

I can only guess that water got in near the cable SMA connector inside the covering sleeve and increased the impedance/resistance to very high because comparing the RSSI of planes now, i can see a +10-12 dB drop on planes that are near me, when before i’ve seen -4 dB, -4.5 on these planes, now i see -14, -15 maybe higher

here is the current situation

here is how it used to be (green plot was max range)

Either water somewhere in the coax / connectors / antenna or the SDR is bad.

You have a short coax or can connect the antenna directly to the SDR?
With the SDR maybe on an USB extension?

With the antenna inside you could then compare RSSI with and without coax.
If the difference is as high as your drop you know it’s the coax.

Testing if something in the SDR has died is basically only possible by getting a replacement.

I tested with different SDR V3 (nooelec nesdr smart), new sdr dongle, never used, still the same.
Coax is short, (5-6 meters maybe less). SDR was connected with extension, i connected it directly to PI, same result also used all 4 usb ports (anyway they are connected to the same hub and shared with ethernet connection so nothing there)

I am going to bring down the antenna and connect it directly to the SDR inside and see how it performs, and then bring the outside cable to the same position inside the house and check.

At this point, the only thing untested is different PI and different cable.

Also worth to note that my apartment is in an attic villa, roof is wooden.

Well it shouldn’t be the same.
The FA Pro+ has an LNA (low noise amplifier) built in.

If they both deliver similar RSSI when set to the same gain then the FA Pro+ is defective.

Let me do the test with and without cable with FA Pro stick and i will get back with results.
TBH i didn’t check the RSSI when i tested with the other dongle, but i’ve seen the same number of aircrafts (low number) but even with no LNA, i should still see at 150Nm to SE direction

LE: did the test, but due to testing inside the result was the same: 9/9 aircrafts with antenna directly connected to FA Pro+ stick, and the same with cable brought inside with the antenna in the same position. This is not a good test, as inside the walls are thick concrete, so only very strong signals area coming through.

I will buy some RG6 cable and move the PI outside in a box , as the cable was inserted via the roof inside and then when my attic was revamped, some false walls were installed and i left a hole in the wall with a plastic box to have the Pi, network cable and antenna cable.

No idea how it stopped working because nobody pulled the cable from one side or the other to have it stressed out or something.

Everything was working properly until it didn’t, the only action i did was to upgrade from Piaware 4 to 5 but performance did not degrade right after the upgrade but 24h later.

We also had some thunderstorms, but i figure if any lightning hit my antenna i would have everything fried.

After i removed every connector and heat it from a distance with a heat gun, along with the end connector from the LMR cable which stays outside, basically it’s the same result, no aircrafts seen after 100Nm. Antenna has a 360 view, it’s above the house roof with 1.5 meters or more.

Maybe the LNA inside FA Pro stick went bad ? I figure it would be inline with the whole circuit, so if it goes bad it will not receive anything. I am saying this because i deployed Piaware to the other RPI 2 with “normal” stick (no LNA) and it’s the same range and number of aircrafts.

I suppose you have measured the Bias-supply. Can only suggest to make a quick 1/4 wave antenna, hook it up and compare. It is useful to have such an antenna around that you can use for quick comparative tests.

How do I measure the Bias-supply ? I don’t have any external LNA.

It’s FA Pro stick → SMA connectors LMR 195 cable → FA antenna

LE: i did all kinds of tests, using a whip antenna which came with NOOELEC stick and with the stick itself, and i have more aircrafts inside than with original cable and FA antenna which is outside.

FA stick behaves as the LNA is somehow dead but not shorted (i.e., not amplifying but passing thru the RF signal) and also the cable might have been stressed out.

I bought some RG6 and i will move the PI today outside in a weather proof box closer to FA antenna and also use a satellite LNA but i need first to find a 47ohm resistor to hook up my HP charger which outputs 19.5 volts so it drops down to ~16 volts needed for LNA.

I have also a power inserter for RF which i used before with a D903 LNA which dropped dead a few months back.

Anyway, these things break, as the FA stick worked 24/7 since 2017


seems that prostick plus stick went bad (from the looks of it LNA stopped working but still passed “normal” RF signals).

went back to the same cable and FA antenna, nooelec v3 stick + FA filter and satellite LNA powered by a 15v adapter with power inserter i was using before.

set a gain of 38.6 after some trial and error and this is the result:

I will do further tests without FA filter this weekend as i live outside the city in a fairly rural area and 20km south from the main airport, but my antenna is very close to a power cable (230v) , maybe 2 meter close, no idea if this induces interference near 1090mhz or not.