FlightAware Discussions

Outdoor antenna works indoor only

Hi,

Until now I’ve been feeding using a small cheap indoor antenna, and everything worked fine. Recently I moved to a new location, at a high floor apartment, and decided to upgrade my setup. I purchased a new outdoor antenna and some strange things started to happen.

I use a Raspberry Pi with a FlightAware Pro Stick Plus, and this antenna: amazon. com/gp/product/B00WZL6WPO

When I assemble the setup indoor and place antenna next to the window, I get an excellent reception, with 100+ nmi range. However, once I bring the antenna to my balcony it suddenly stops receiving any signal. While it is my hand it can register some occasional messages; however, once I fix the antenna, it doesn’t receive anything. I check if I’m receiving anything by looking at the dump1090 UI.

Also, I made the following interesting observation. The antenna has an N-type connector. Once I unscrew the connector almost to the end (about 1/2-1/4 turn left), the antenna suddenly starts receiving the signal again.

So, it turns out that the antenna only receives the signal when it is either inside, or almost unscrewed from the cable. With almost unscrewed cable left for a day, I’ve got 200+ nmi range. However, I don’t feel that the N-type connection should work like this.

I did the following troubleshooting:

  • Bought a new cable and got the same result. So, I tried these two cables:
    - https://amazon.com/gp/product/B07R3BKMZN
    - https://amazon.com/gp/product/B07J54LCL7
  • Tried playing with the cable position, moving the antenna and the receiver around, and slightly bending the cable in different directions right next to the antenna connector. As a result I found that the outcome with the tightened connector seems to only depend from the antenna location.
  • Tried slightly bending the internal parts of the connector to ensure there is definitely a solid contact inside. This didn’t help as well.
  • I connected my old antenna to the receiver. It received the signal from any position without any issues.
  • As the system doesn’t work in the configuration where it is supposed to have the best reception, I thought, that potentially, there could be a receiver overloading. I tried various gain values for dump1090-fa, including AGC. None of them worked.

At this point I’m out of the ideas what can be wrong, and asking for some help. I have my feeder running with a barely-screwed antenna now; however, I don’t think that is how the system is supposed to work. I’d appreciate any recommendations and suggestions.

Thanks.

You are suffering from overload caused most likely by mobile phone signals. You will need a filter.
Your symptoms are the same as in this thread:

2 Likes

Not quite sure if it’s really the same. He’s using the blue Pro Plus stick which includes already a filter.
I have the same setup outdoor without issues. I only needed to adjust the gain fo routdoor usage.
I bought the additional dark blue filter, but attaching it doesn’t give a difference.

He stated that the device stops getting any signal. Even with an overload i would expect that at least some signal should appear

I’m 99.9% sure it is overloading. I too use the blue ProStick plus (as was the the post I quoted) and without additional filtering it overloads at my location. The problem comes from intermods generated in the circuitry before the filter. If you have such strong signals that you overload the front end, then the gain control cannot help, as the gain does not have any effect on these front end devices.

1 Like

Before buying new stuff i would simply install tar1090 and graphs1090 for getting evidences

ok, and i am still with the 0.01%
If it turns out that i am totally wrong, i am also fine with it.

It attenuates the signal.
That can help reducing the interference to a level the FA Pro+ builtin LNA can handle.

There is no reason why the interference can’t be strong enough to kill reception completely.

I’d recommend going straight to this LNA, it has good input filtering and has proven that it can handle very strong interference:
https://www.rtl-sdr.com/product/rtl-sdr-blog-ads-b-triple-filtered-lna-bias-tee-powered/

You would also need a bias-tee to power it or switch to the rtl-sdr v3 SDR and power it using that.

But the FA barrel filter will likely also work and might ship quite a bit quicker :slight_smile:
(last reports on the rtl-sdr shipping from china to the US: 3 weeks)

Installing graphs1090 isn’t a bad idea.
https://github.com/wiedehopf/graphs1090#graphs1090

I’d recommend setting gain to 43.9 and showing the graphs here if you don’t want to blindly get a filter.
On the other hand if the FA filter is available, it’s not that expensive usually and the symptoms really point to some sort of interference.
Do you have other antennas or satellite dishes in the vicinity of where you mounted the antenna?
If so you can try unpowering that equipment and check if anything changes.

With a blue Pro Plus stick wouldn’t he need to be directly beside any of these transmitters to completely block the 1090MHz signal?

That was also my idea. I think this gives us some input on what’s going on . Also checking the logs would help at least to verify that the software is running properly

I can remember a case where my device stopped working whenever i moved it to outdoor. Reason this time was a bad connection of the USB stick to the device.
But then the logs should tell you what’s going on

He also mentioned the cabling. I would test exactly the same setup outdoor without exchanging or disconnecting anything in between. A whever broken cable can have the same result

My case falls in the 99.9% :wink:

That is a setup we can work with. The Threadopener need to do something similar documented.

Let me know if you find the two days where i had the additional dark blue filter installed.
Hint: It was not Tuesday/Wednesday

What i want to say is that a filter is not necessary THE solution in all cases. The investigation must go deeper

No.

The Pro+ is much more susceptible to strong interference actually because the LNA on the input seems very prone to overloading.

A normal rtl-sdr chip would likely work in the same location.

1 Like

OK

then i am stepping back and watch the results of his problem investigation

The symptoms are the same of my two setups (both prostick plus). Famous workaround to unscrew the connectors to solve it…
after I added the FA dark blue filter 1090, problem has been solved !! I am getting signal up to 330 NM (I am in Cagliari, Sardinia island, and I catch airplanes landing in Malta (not always, but often).

I feel to address our friend to try a FlightAware Dark Blue Filter 1090. I solved all problem with it.

This is my experience as discussed in a few other threads.

If the “built-in” filter isn’t the first component in the receiver chain (after esd protection of course) then the LNA can simply “give up” with a strong signal anywhere in it’s frequency range.

A little update here: after adding a standalone filter everything works like a charm. Thanks for all the replies!

I have yet to confirm, but someone from FlightAware should be able to easily chime in on whether or not this is correct:

I believe the FA Orange and FA Blue radio use the SKY67150-396LF for their amplification. Per spec @5v, this chip has a nice, high IP3 of +38dBm (In a nutshell, the higher the better for saturation purposes). Most alternative low(er) noise amps fall between +30-35dBm for comparison.

That said, I think they opted to feed the chip 3.3v to help keep the power consumption down (remember the USB port needs to power all this on top of the tuner). Unfortunately Skyworks doesn’t have 3.3v specs in their datasheet, but besides some positive effects (lower power consumption, lower noise factor), doing so also lowers the IP3. Comparative chips have measured 8-10dBm drops when being fed 3.3v vs. 5v.

So now we’re looking at an amplifier running with a lower linearity intercept making it much more predisposed to saturation. This is why both of these radios tend to perform better with some sort of upstream filter.

This is my theory and still need to take one of my metal cases apart to confirm (stuck mine in metal cases for cooling and shielding). I suppose anyone from FA could save me the trouble…

I suppose if this is the case, and some run their radios though powered hubs, there could be another thread on how to mod these things :yum:

1 Like

I solved it like this: used Generic Dongle with Triple-Filtered LNA + Bias-T + 5V dc power adaptor to power the LNA through Bias-T.

OK, then i apologize for not believing it.

Just experience the same issue after removing the FA filter, I’m using the Prostick Plus with the “refurbished” Jetvision antenna.
Probably my setup is very close to saturation.
Does anyone ever tried to install a variable attenuator before the RTL-SDR dongle?

Not continously variable, but stepped like this:
3 dB (attenuator #1)
6 dB (attenuator #2)
9 dB (attenuator #1 + #2)

https://discussions.flightaware.com/t/announcing-the-pro-stick-plus/19202/125

It showed that at my location, the RF interference is so bad that without an external filter, Pro Stick Plus’s front-end LNA gets saturated, and performance drops to near zero.

However if attenuaters are added, these dampen the interfering signals and performance shoots up even without an external filter.

 

It would be interesting to have a PE4302/PE4312 controlled by the Raspberry that would allow change the attenuation by SW.