FlightAware Discussions

Impact of aircraft type or airline on signal strength?

Today i was looking a bit longer on my map and was monitoring a bit the RSSI values shown on the receiver

It is clear that aircraft closer to the receiver normally does have a stronger signal.
But how does the used aircraft or even the airline does have an impact to these values?

I have aircrafts/tracks with obviously stronger signal far away compared to others much closer. And in the opposite closer aircraft with less signal value.

Example from this moment:

The KLM is 150 km away (sorry for switching to km @wiedehopf :slight_smile: ), also the NetJets while the Lufthansa is close but with weaker values

image

Especially aircraft of Ryanair always pop up with strong signal, independent from their distance.

Or is this all just by chance based on the current conditions?

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Some people (on this forum) think RF is easy, but this is a simple example showing how fast it gets complex.
Different aircraft have the antennas in different locations. Different manufacturers may have different output RF power. The shape and material of the fuselage will affect to radiation pattern. At certain angles, the engines will obscure under-mounted antennas.
The radiation pattern is unlikely to be (truly) omni-directional, so the (your) RSSI will vary depending on the planes relative bearing.

It’d be interesting to remap the altitude colours to show RSSI to see what is dominant.



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I hope you are not pointing to me :slight_smile:

As i am not an expert on this topic, i was just curious and would like to get more details about it.
Your post makes sense to me and the pictures are pretty interesting and explain some things to me.

Not at all.
It’s an interesting question without a simple answer - a real rabbit hole!

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The Radarcape devices are also showing a signal level, but different values than the RSSI values. That’s also part of my thoughts as non-expert :slight_smile:

Here is something to think about - if you have a light, slow low flying aircraft, you can punch a hole in the skin and mount a conventional antenna like this


But what do you do if you have a fast, high flying composite aircraft that doesn’t offer a ground plane?
You embed a 2-dimensional antenna in the composite where the antenna isn’t the conductor, but rather the hole in the conductor
image
Skeleton Slot Antennas are well into the “weird” of RF behaviour.

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I was going to use one like that on an alloy plate but at $30US I decided that a piece of brass welding wire was cheaper.

Then I found I could make a CoCo with some gain and moved on.

So as not to be completely off topic I watch aircraft coming and going and B787s particularly are visible about 30NM further away when they are arriving compared to departing.

S.

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There is also some range in allowed transmit power from https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2020-165.pdf p28


1090MHz:21dBW=125W 23dBW=200W 27dBW=500W
978MHz:12dBW=16W 16dBW=40W 24dBW=250W

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I categorised 24 hours of data from timelapse1090 according to aircraft type, and took the top 5 most common types:

Boeing 737-800
Airbus A320-232
Airbus A320-251N
Boeing 787-9
Boeing 777

Here is the distribution of signal strengths according to type:

image

There’s some slight variation, but this doesn’t account for the position of the various aircraft.
Here is the same data binned into 50 mile increments:

Range affects signal strength to a much larger degree than there is any variation between aircraft types. There is some small variation between types but whether there is any significance is questionable since aircraft of the same type could have different avionics fits. It’s also possible that data aggregated over a longer period could provide different results.

Here is the distribution of signal and range of the top two most frequent aircraft for this days data:

Again, I don’t think there’s much of significance to be concluded other than that range has the largest effect.

Data in tabular form:

Count is the number of data points, not unique aircraft. The number of unique aircraft of each type is:

image

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Nice body of an A320 :slight_smile:

But it’s interesting to see that the Boeing does have a similar shape if it comes to signal strength.

Based on my spots of vieweing i would have expected the B738 models more like the A320

Great work, @caius

Searching for “adsb range vs rssi” one result was a graph of RSSI vs range from p8 of https://www.cs.ox.ac.uk/files/7238/ipsn2014.pdf

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