What are nominal ADS-B signal levels?

I raised my antenna 15’ by placing it in the attic near the underside of the roof. As a result the average and maximum distances have dropped. Can the added 15’ usb cable cause this? The signal strength is in the -30dBFS range. Will an LNA improve the range?

Many thanks to wiedehopf for the graphics.


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Depending on the roof material the additional height won’t help.

What gain setting are you using?
Looks like you need to turn it up.

Regarding the USB: if you can make sure there are actually 5V arriving at the dongle it should be good.
But that’s hard to guarantee unless you use a voltage regulator at the dongle.

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Gain is set to -10. Roof material is standard asphalt shingle over tar paper.

What antenna/coax are you using?

That’s really weak reception even through the roof.

I’d suggest either one of the DIY antennas or trying a PCB antenna.
An LNA will help, but i’d improve the antenna first.

But if it reduced your reception, placing the antenna under that roof might be suboptimal.

On one of your station your reception was clearly better on Tuesday:

So whatever you did that day, improved reception at least a little bit.

I’ve use 3 different antennas with similar results.
Ground plane with 4 radials w/SO239 to sma to mcx with on 6" of unknown coax between the sma and mcx connectors.

Ground plane with 8 radials w/F-type to sma to mcx adapter with 67mm rg9 between radials and F-type (like ABCD567 spider diagram) to sma to mcx with 6" of unknown coax between sma and mcx connectors.

FlightAware ADS-B antenna with SO239 to sma connector direct with no cables.

The USB cable is 15’ of type 3.0 connected to inside of wall plate with another 2" of USB type 3.0 cable from wall plate to RPi.

Tuesday early morning was when the antennas were moved to the attic (temperatures exceed 140°F, 60°C).

The Flightaware antenna uses an N connector, not SO239.
Cables from N to SMA are a little expensive but worth it: https://www.amazon.com/dp/B00H9II88C

Maybe your SMA to MCX adapter is bad?
Anyway just get a good dongle with SMA connector, one of those will do:

The v3 might cope with the heat the best though.

I’d not recommend this kind of USB extension.
Just place the entire RPi up there?
Give it a fan maybe?

I have a FlightAware Pro Stick and 2 generic DVB-T 820T2 sticks.
I’m afraid there might be too much heat in the attic for the RPi to survive. Our real heat is a month away.

I was guessing at the names of the connectors. I used the ones that fit. I have both genders of each adapter along with a bunch of mcx hardware.

I don’t think the dongles survive the heat any better than the RPi.
Also i was recommending a fan like this, cools both the dongle and the RPi.


You can clearly see when the fan was installed, temperature of the RPi dropped by 20 C
With the fan i’d say the RPi never goes more than 10 C above ambient.
So even if your attic gets to 60C, with a fan that should work.

Anyway installing it there is of course quite the chore if it’s that hot.
And having the RPi somewhat accessible is nice.

The problem seems to be that the reception isn’t even any better below the roof.

What happens if you connect the FA antenna with the SMA adapter directly to the FlightAware ProStick.
You obviously have some USB cable to connect it.
I’d just suspend the antenna from the ceiling wherever your RPi is.

Do you mean you moved them up only Tuesday and then moved them back down?

Running the rtl-sdr LNA would sure work in the attic.
You could get relatively inexpensive cable from the attic to the RPi and attach the LNA directly to the FA antenna.
To make sure the rtl-sdr LNA doesn’t get too hot, i’d get a bias-t and feed it with the 3.3 V rail from the RPi.
Or use 5V and a 20 Ohm resistor.
(Feeding it with 5V direclty will make it run rather hot)

OBJ has mentioned in a few posts that long USB cables cause a lot of problems.

I have four RPIs in my attic (plus an ordoid XU4, Odroid N2 and ulari APRS transceiver). I did have a radarcape but it stopped work (I checked and it can handle the the heat. It is a flash card issue). They have been there for years with no issues.

The RPI POE unit (For 3B+s and 4s) is pretty good at keeping the CPU cool. The generic fans also work well. I had to put one on an RPI2 years ago to keep it cool enough to run an airspy(it would get overloaded and throttle the CPU. Even the RPI3B+ isn’t enough for an airspy in my location).

I bought some larger heatsinks to try to keep the dongles cool. The adhesive tape doesn’t like the heat. I need to use some cable ties, I think.

I moved them up on Tuesday and they are still there undisturbed.

The FlightAware antenna is connected directly to the dongle with no cable. The dongle is connected to the RPi via a 15’ and 2’ usb cables. I’m not sure if the feed is 102540 or 104282. As of 13:00 I disconnected it and hooked up a feed using a magnetic whip antenna on a 4" x 8" steel plate that is only 6 ft above ground lever (95 ft ASL). The difference should show up in a few minutes. For some reason that RPi refuses all web connections so I can’t look at the graphs. :frowning:

I’m investigating installing a new RPI (on order) in my garage where the temperature maxes at 97° F (36° C).

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Has anyone tried to keep hi Pi and Dongle inside a Fridge / Freezer / Deep Freezer :wink: :stuck_out_tongue_winking_eye:


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Well according to the FA stats it worked well for around 7 hours or so and then went back to approximately the old reception.
So that’s very strange.

Which dongle did you use?
Directly connected to the FA antenna i would expect much more signal.
Maybe the adapter is incorrect or not screwed on to the antenna far enough.
Very strange.
(a photo of both ends of the adapter you used might be helpful)

No matter where you put the RPi, use a fan!
And i’d recommend the v3 dongle, it dissipates the heat well.

Maybe all your dongles are just heat damaged :wink:

I’m really not sure what the problem is, but there is definitely something wrong.
Maybe it’s just that the antenna is not outside.
Or you are surrounded by high houses? Trees?

The next time I enter the attic I’ll take photos. I have several surrounding oak trees. KTPA is located 12 miles ESE so they are blocked. I’m in a condo villa so I have a shared wall to the North. West is an open golf course. We have 1 and 2 story houses with 16’ ceilings.

The temperatures on 101435 are consistently between 55° C and 60° C. There is no cover on the case holding a RPi 3B. Ambient air temperature is a steady 74° F ( 23° C).

The FlightAware antenna and dongle is new. I also have their external filter, but have not installed it.

Trees plus having the antenna inside combine to give bad reception.

Still the few hours of better reception on Tuesday show it’s possible to get a little bit better reception.
I’ve already described a setup with an LNA in the last post.

Performance will still not be stellar with all the obstacles.

Can you suggest an LNA that uses external power instead of bias-t from the dongle?

You don’t need a dongle with bias-t.
You can use something like this and feed it with 3.3 V from the RPi: Bias Tee Wideband 1mhz-3ghz for Ham Radio RTL SDR LNA Low Noise Amplifier 50vdc for sale online | eBay

There is the uputronics LNA which can be supplied via USB, that’s easier to handle.


I believe that I found the answer. At 13:00 today I disconnected from an attic antenna and connected a whip antenna on a steel plate next to the RPi. The graphs show dramatic improvement. I believe that by lowering the antenna the signals are passing under the tree canopy. :smile:


I’d speculate the adapter has no pin on the SMA side or something like that.

The FA antenna should work much better if you use it where the RPi is.
Unless the adapter is bad, which is my guess.

This is what the ends of the adapter should look like:


Be carefull with the N and SMA connectors.

The 75 Ohm N has a smaller pin.

Picture showing the similarity between 50 Ω (bottom) and 75 Ω (top) Type N connectors

SMA and SMA-RP are easily confused.

SMA Male connector, SMA Female Connector, RP-SMA Female Connector, RP-SMA Male Connector