FlightAware Discussions

Mysterious issue/phenomena with connectors/Pi/Prostick

Good day to everybody.
I am getting an incredible strange situation and not able to face/solve it.

Setup 1:
1 Raspberry Pi 3B+
1 FA Prostick Plus
1 coax adapter SMA-BNC
1 BNC male connector for coax cable Ecoflex10 (rx side)
18 meters coax cable Ecoflex10
1 N male connector for coax cable Ecoflex10 (antenna side)
Several antennas tested: FA ADSB Antenna 66’ / GP1090 Slovakian ADSB antenna / DPD Antenna ADSB
3.8.1 PiAware version

Antenna is well connected to its cable and installed in a mast telescopic pole 4 meters above roof.
If I connected right well all connectors male to their female (N and BNC, SMA and so on),
air traffic received by this setup drop to 0 zero… with 0 or 0.1 msg/sec indicated.

If I make micrometric movement going OUT from female connector (prostick plus side), I find a right position where air traffic signals are received, airplanes are plotted and msg rate raise till 100/200 msg/sec (depends time)!
Male connector is just a little inside its female connector of the coax adapter BNC to SMA, not well inside.

What hell is happening?

Connectors are well done and tested.
Cable is new.
Connecting same antenna/cable/connector to an old Kinetic SBS-1, it works like a charme with no any “game” to do in the coax connector, a BNC well connected, that’s all.

Tested with other Raspberry, other Prostick Plus… same strange problem.

I’ve tested another setup with other hardware different from setup 1.

Setup 2:
1 Raspberry Pi 3B+
1 Prostick Plus
1 pigtail SMA to N female
1 N connector Messi&Paoloni for Ultraflex7 coax cable
10 meters of Ultraflex7 coax cable
1 N connector Messi&Paoloni for Ultraflex7 coax cable
Several antennas tested: FA ADSB Antenna 66’ / GP1090 Slovakian ADSB antenna / DPD Antenna ADSB
3.8.1 PiAware version

different location in my home, different Mast Telescopic Pole (there is a disconnected V dipole just installed)

Keeping a bit out the N connector, just 1 or 2 turns, WORKS, if I continue to turns it and make a stable connection with its female… DROP TRAFFIC, 0 messages.

When I connect to these setups the little SBS-1 antenna with magnetic base mount, ALL WORKS very well (just limit of this small antenna).

What happening ???

I made thousands tests, remade all connectors, tested, and so on!

Thanks for any help

You are suffering from too much signal overloading your dongle.
When you unscrew the connectors you are introducing attenuation and no longer overloading things.
You probably need to reduce the gain of your receiver and more than likely will need to use a filter.
It’s a long thread but see:

LawrenceHill thanks a lot for your prompt reply.

I’ve made alot of test changing gain of the Prostick Plus, but never had success.
Only airplanes around my ATZ are received, outside signals become to be lost.

I’ve read again that topic (long yes, but I’ve read and followed it in the past) and I’m still thinking…

A friend of mine, is experiencing the same problem (same configuration).
FA Antenna was installed on the top of a mast where there is TV antenna lower.
Same problem, need to let “soft” connection (with BNC/SMA).

He tried to install the FA Antenna in a wood mast and magically ALL WORKED.
He tried to install the same antenna in a different typical mast (zinc iron), but at 3 meters from previous TV antenna mast and it still works like charme!

In my case… my main mast has different ham antennas plus 3 TV antennas lower, and I have this problem.
In second setup, my mast is another, with only an HF ham antenna V dipole in aluminium and I have this problem too.

Reporting that because sometimes I can have suspect of some electrical issues provided by TV antennas, but other time, with no TV antenna in the mast, there is still the problem…

Sounds like inter-modulation products causing interference.
Check the metal mast and TV antenna for corrosion:

The LNA is in front of the filter and will be overloaded.
Changing the gain doesn’t change the initial LNA, so when it’s overloaded you can’t do anything about it.

You’ve spent enough money, easy enough to get the FA barrel filter.
With lots of transmitters on the mast, you might even need 2 of them in a row (not even kidding).

A cavity filter would be even better, but those are heavy and expensive and i’m not even sure there is a supplier in the US.

If you have another non-FA SDR, you could test with that as it won’t have the LNA as the first link in the signal chain and might work better.

Good luck.

So you’re saying the issue is with a metal mast with a TV antenna on it?

Does the TV receiver box source current into an amplifier at the TV antenna?
That could either produce some sort of DC offset issues if there are grounding issue.
Can also couple over noise.

Can you switch off all equipment connected to the mast and check if that improves things?

it’s an interesting scenery (I didn’t know anything about it).
But watching all parts, they are enough new, I don’t see evident sign of corrosion or rusty bolts.

I’ve made some tests with no any other ham antennas connected (just the 3 new TV antennas on the base of the mast, I cannot disconnect them to avoid… TV issues of my neighbours.

Yes, you are right. Maybe I have to test my setup with this FA dark blue filter… but it’s so strange this phenomena. All ok in other frequencies below (VHF/UHF).

I could try… but I have a Noolec SmartSDR, maybe trying to install it on Raspberry I could make further test…

All three TV antennas are logarithmic models and their 75ohm coax goes down directly to the house, I think there is only a passive mixer to put TV IN in some rooms. No any active and powered devices along the TV line.

Well try disconnecting it at the mixer and see if something changes.

Sorry, I’ve explained not well. Each antenna has own cable that enter inside house of my neighbours, unable to enter in their houses :smiley: as it could be very hard to disconnect their antenna from cable on the roof.

By the way… problem has been experienced also in another mast with no any TV antenna (just a disconnected new HF antenna V dipole)… so, could TV plant be the source of problem?

I understand there are so many variables:

  • overloading signals, maybe a 1090 filter could solve, because ProStick Plus gain change failed;
  • inter-modulations due to rusty bolt, but happen in three different masts in different locations and it doesn’t seem there are so the conditions;
  • TV plants interaction in two masts, but in another one without TV antenna, same problem;

Further test to do, as suggested by wiedehopf with a Noolec SmartSDR instead of a FA Prostick Plus.

A few thoughts and a joke or two:

  1. a 66 foot antenna is a lot of antenna and I didn’t know that such a thing was sold by FA. I’m guessing you’re on the 26" and you’re mounted 66’ in the air. Is the FA mount electrically isolated from the mast?

  2. You mentioned you’re using multiple connectors. Can you test all connnectons with an ohmmeter and post a result? You’re at around 60 feet of coax. I don’t think you’d be at 100% loss if your connections were solid. Which leads me to…

  3. Look closely at the antenna/coax connection. I’ve been unable to find where I read this, but it’s been said that the FA antenna and coax connection isn’t normal. Like, to the tune of a complete disconnection, a female where a male was thought to be, or as you described in some of your feedback - intermittent connectivity.

I would - if you can afford to - look at another radio option as a test in place of where the FA dongle is currently.

You’ve described several things. The last thing you mention is loosening a connection and receiving data but when tight, indicates 0 messages. If you’re looking at this frustrated - I would be also at first. But reroute your frustration to the basic issue - you’re creating a short somehow when tightening up the connection. So look at those connections. You might even find something that’s actually creating the short by analyzing the actual connections in detail and attempting to gain knowledge on if you have metal on metal contact.

I cannot think of a software based test for this. I do believe the FA dongle does have short protection in it, but if you’re having a short and it’s protection has failed, your dongle/internal amp should also either cutoff or fail permanently.

You could also have a male connector going too far into the antenna, also potentially creating a short condition. Food for thought.

Good luck and don’t fear reaching out.

Wondering if somewhere in your adapters, you have SMA-RP which will be missing the center pin vs a conventional SMA…
Based on the symptoms, that would be worth a look.

1 Like

He doesn’t seem to be a native English speaker, so I would bet that what he meant was a 66cm antenna, which coincidentally, is 26 inches.

If that were the case, how would it get better when he unscrewed the connection?

What is the reason for using BNC connections? (this question doesn’t matter, I am just curious)

It appears that BNC connectors are available in 50ohm and 75 ohm variants, and that they are not interchangeable. Which version are you using? I am wondering if the center pin might be smaller in diameter than the socket inside the SDR.

Can you compare the center wire in the BNC connector to the center wire in the magnetic antenna connector to see if one is thicker than the other? My guess is that you will find that the BNC connector has a thinner center wire, and when the connector is tight, the wire isn’t actually touching anything inside the ProStick Plus. When you loosen the connector, it “tips” a little bit and allows the center wire to make contact at an angle.

Another thing you could try is when you have the connector loose and the system is receiving messages, wiggle the wire and see if the movement causes the reception to come and go.

Hope that helps in some way.

I would be willing to test the prototype for FA, assuming they paid for shipping…

This is 66 cm / 26" (inch) FA Antenna, with plastic pipe removed:


Yes, my mistake, 66cm famous FA ADSB antenna. I am italian, no native english sorry.

I made this test with my digital tester. I’ve disconnected coax connector from Prostick Plus and made test on the BNC male coax connector that runs toward antenna through Ecoflex10 coax cable.
Checks between central pole and metal case of the connector:
OHM = infinite
Vcc = -0,120 to +0.110 Volts
Vca = about 0,140 Volts (sometime up to 0,160 Volts)