FlightAware Discussions

FA 1090 Antenna Problem

Just moved my PiAware and Antenna from attic to rooftop and have a curious problem. Almost no signal is now received when the FA 1090 antenna is mounted at the highest point of my roof via an eve mount. However if I slowly unscrew either connector, good signal is received just prior to the connector coming off. It seems as though the signal is received when connection to the outer screw part of the connector is broken and just the center connector is hanging on. I have confirmed that the ProStick and female connector is fine by using the small dinky antenna which works great up there too btw. I have replaced the cable which now has same result as the previous cable. Seems the issue has to be the FA1090 Antenna which is almost new. I did use the FA 1090 Antenna in the attic for a week with zero issues except signal blockage. Any ideas?

  1. Could the antenna have simply gone bad when I moved the antenna to the roof?
  2. Is it an issue if the metal screws going into the antenna mounting place are touching some kind of metal in my eve as they were screwed in?

Thanks in advance. I am hoping this is something simple that I am missing. For now, I am getting 100-125NM range with cable connector barely hanging to the FA 1090 antenna but obviously this should be much better with about 35’ of elevation in the flat midwest.

Are you in a noisy RF environment? This sounds like overload. If you can move the antenna without a lot of hassle, try bringing it back to the attic and see what happens.

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Good suggestion; I actually hadn’t thought of that. I am not aware that the environment is noisy but hard to know without a spectrum analyzer right? Also, I thought the 1090 filter on the PROStick was supposed to aid with noise? Pretty typical suburban neighborhood. I will try this and report back. If we are talking noise, I would have expected that losing the shielded connection would make things worse not immediately and distinctly better. But I have a lot to learn. The odd thing is that it goes from absolutely nothing received with the antenna properly connected to the cable and then fairly decent coverage with just the center wire connected (or at least that’s what I think the condition is)

If you fancy exploring that with the kit you have, take a look at this topic which explains how to generate heatmaps showing what the radio can see. Try @obj’s suggestion first though if you can.

I brought the antenna back to the attic for troubleshooting and sure enough the performance was back. Since I ultimately want to optimize system performance, I have remounted the antenna back on the roof and am awaiting the additional FA filter to see if that will help. What’s interesting is that with the FA ProStick (which includes a filter) and connected to the FA 1090 antenna, the system receives absolutely nothing!

I admit the thread title is incorrect and that receiver overload is more likely the issue. I left a spare RTL dongle in the Pi with a descent antenna and will see if I can manage to get a spectrum analysis. Thanks.

Are you using the same piece of coax for both locations?

Yes, same coax. No changes to the system except the location and method of mounting the antenna (attic mount was temp, roof mount is permanent with the provided bracket).

Another possibility is that there is a signal riding in the ground in the roof connection. How is the antenna mounted on the roof.? I assume the FA Ant is clamped. to something. Is there a circuit path there?

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Thank you cwalker. Yes, that is possible. To check that I removed the antenna from the mount and just held it. Same result.

To answer your question, I have shaped a wood triangular piece to the eve and used 4 screws to mount it into the eve. Then I have simply attached the FA 1090 antenna provided bracket to the wood piece. Next time I am up there, I’ll take a picture :slight_smile:

Could it be the case that there is a short circuit between the inner and the outer of the coax, possibly at a plug end related to how it’s been attached, which depends on the way the coax is flexing and that when in the attic it flexes / stretches such that the short isn’t present, but when on the roof it flexes / stretches differently such that the short is present?

I appreciate you’ve tried two cables but if they were a pre-made cable from the same batch, or a particular batch of coax, or you attached the plug but made a small error in the method each time, it could be the case that they both fail in the same way. Eg a single strand of braid free to move around in a plug. To test that you’d have to check for continuity between the inner and the outer when in the non-working position, and probably disconnected from the radio. I think it’s unlikely to be this but just throwing ideas out there based on what’s observed.

Does this tell us anything? The is the capture with the recommended settings for 30 minutes at the rooftop location from the FA 1090 antenna and ProStick.

It shouldn’t look like that. Here’s what mine looked like a while back at different gains. Your image appears to show the reason you’re not seeing signals, whatever’s causing that whiteout at 1090. It’d be interesting to see it with just the center part in which you mentioned was showing signals, and also connected normally but with the gain set down in the 20s

testing_withpreamp

Thank you for the suggestions Chris. The first was rather thin and the second is a low loss rather stiff cable. I will ask one of my electrical engineers at work how to check continuity on the cable; thank you.

Yes, same coax for both locations.

Do you have a TV or other antenna system on the roof?
Does the coax run parallel to any such system?
Is there an antenna system on a nearby roof, which the antenna might be somewhat shielded from in the attic?

My guess is you just have strong interference on the roof and just don’t know it yet.

Once the interference is stronger than a certain threshold, the LNA in the ProStick+ starts putting out only noise basically.

Thanks all for responding and helping me work through this. So I have wrapped foil around the ProStick and added the 1090/978 FA filter in addition to the filter already in the ProStick. Finally seeing some traffic. It’s actually quite good but not at all the range I was expecting at 35’ AGL with a clear view of the sky. When I have time I plan to re-assess the spectrum analysis at various gains and also take some photos to better show the installation. Thanks again to all that responded!!!

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