What is the Maximum Range I can Get?

[yvesprairie]

Hi all,

I’m a newbie at Flightaware so bear with me. Everything is working as it should except that the range my antenna can see seems to be ridiculously short. I have a good ADSB antenna (the flightaware one) and it sits that the top of a 4-story building. Although there are definitely some obstruction on some parts of the horizon, large portions of it are clear. Yet, all the planes that I can see on flight aware are only a maximum of 2 or 3 nm. I have a 25 foot long cable, could the quality of the coax degrade the signal that much??

Anything insight would be appreciated.

Regards, Yves

[foxhunter]

with such a short range there seem to be something else wrong.

Please share some more details about your setup
Which antenna
Which cable etc

It could also be a bad connection. In the past people were struggling using the wrong SMA connector, missing the middle pin. Have seen such a setup and it showed exactly your problem.

Just an idea, could be also something else.
If you’re using a Raspberry, which type of setup do you have? Flightaware image or package on top of a Raspberry device?

What are the settings of dump1090-fa regarding gain?
You could setup the good graphs1090 script to check more details.

[wiedehopf]

could be the wrong SDR chip.

Can you link all the stuff you bought?

antenna, coax, SDR …

Might also be that you need an extra filter due to some antenna close by producing interference (mobile tower, something).

[yvesprairie]

Thank you for your quick replies. Here is my setup.

Antenna: https://www.amazon.ca/gp/product/B00WZL6WPO/ref=ppx_yo_dt_b_asin_image_o08_s00?ie=UTF8&psc=1

Cable: https://www.amazon.ca/gp/product/B09BQX46Q3/ref=ppx_yo_dt_b_asin_image_o07_s00?ie=UTF8&psc=1

together with male SMA to female RP-SMA converter

SDR receiver: Nooelec NESDR Smart v4 Bundle - Premium RTL-SDR w/Aluminum Enclosure, 0.5PPM TCXO, SMA Input & 3 Antennas. RTL2832U & R820T2-Based Software Defined Radio

I use the setup either on my Mac or on the raspberrypi but I don’t think they contribute to the issue I am having.

Many thanks, Yves

[caius]

N Male to RP-SMA Male

That is the problem. It has a reverse polarity SMA plug on it, which means it will not connect to the centre pin of the SMA socket on the receiver.

You need a standard SMA plug which has a pin in the centre. You can get an adaptor that will do the job rather than having to replace whole cable or resolder the correct plug if you don’t want to do that. Something like this will do the job. You can probably find them sold singly if you search around.

[SoNic67]

I am always amazed by this… how come people don’t look to their connectors to see if there is a pin to go in the opposite hole?

[yvesprairie]

But there is… this is why I have the male SMA to female RP-SMA adapter in the first place. So the solution graciously provided by caius is pretty much what I have already.

[caius]

Ah sorry I somehow completely missed that you already had that. In that case there may be some connection problem - have you checked for continuity of the coax from end to end, and that there is no continuity between the core and screen?

If you are getting very short range despite being mounted on a high building there must be something fundamentally wrong somewhere. RG58 is not ideal for that length of coax and could have significant attenuation depending on the quality of the coax (RG58 indicates the dimensions, not necessarily the construction or quality of the cable). It would be worth testing the receiver with a shorter cable run if you are able to do so temporarily for the purposes of elimination.

If you haven’t done so already, it’s also worth installing graphs1090 to keep track of your receivers performance and allow you to make comparisons when you make changes.

[foxhunter]

Any additional connector not working properly can be a source for trouble.

[SoNic67]

I agree. Like when mine just… rusted away!

[abcd567]

@foxhunter

Any additional connector not working properly can be a source for trouble

 

My no-connector, no-coax “Spider-on-the-Dongle” eliminated all issues related to coax & connectors

 

Photo from year 2017
Laptop OS was Ubuntu

 

[SoNic67]

@abcd567

eliminated all issues related to coax & connectors

I disagree. The roof and walls of your house eliminated those issues.

[Bill2002]

Hello everybody…
i have calculated or tested more or less the range with howwhatsthat my range and for my normal antennas it fits perfectly. Today th

ere is something I will show you guys…my new antenna seems to go crazy this days and it shows behavior which is not normal …I have a range about 410 nm… i have no explanation for that …maybe over range reflection ?

[wiedehopf]

@Bill2002

ere is something I will show you guys…my new antenna seems to go crazy this days and it shows behavior which is not normal …I have a range about 410 nm… i have no explanation for that …maybe over range reflection ?

Not from today, but the general idea is this:

Nice bit of tropo over the UK and Europe today

[jimMerk2]

One thing you don’t often see is a link budget for ADS-B links. But, you can show via a simple link budget that with a good setup you can receive ADS-B over 400nm.

For example start with the following:
Aircraft transponder EIRP: 51 dBm (125.8 Watts)

Free Space Loss (FSL):

For distance in kilometers (dkm):
FSL = 32.4 + 20log(dkm) +20log(FMHz)

For distance in nautical miles (dnm):
FSL = 37.8 + 20log(dnm) +20log(FMHz)

where FMHz = frequency in MHz

For nominal range of 200 nm and 1090 MHz:
FSL = 144.6 dB

Signal at receive antenna:

51 -144.6 = -93.6 dBm

Assume antenna gain = 0dBi

So, signal at receiver input = -93.6 dBm

Thermal noise (kTB) at 290 K:
-174 dBm/Hz

Noise figure:

Assume rtl-sdr dongle : 4 dB

Receiver noise:
-174 + 4 = -170 dBm/Hz

Received C/No:
-93.6 - -170 = 76.4 dB-Hz

Data rate (DR):
1 Mbps

Received Eb/No:
Eb/No = C/No - 10log(DR) = 76.4 - 10log(10^6) = 16.4 dB

Required Eb/No = 14 dB for On-Off-Keying (OOK) at 10^-3 BER

So even a minimal system works at 200 nm with a slight margin of 2.4 dB.

But suppose you have a 6dBi antenna, you could receive 400 nm with the same margin. Also, throw in an LNA with a 1 dB noise figure and you have another 3 dB of margin. So, receiving at 400 nm seems reasonable with troposcatter.

[jimMerk2]

One thing I should point out about my previous post is that you can’t really just add the noise figure to thermal noise of -174 dBm/Hz to get the receiver noise level. That’s only accurate for large noise figures like 10 dB or greater. For lower noise figures you need to use equivalent noise temperature to get an accurate noise level at the receiver. So you start by converting noise figure to noise temperature:

NF = 10log(1 + T/290) where T is equivalent noise temperature.
So for NF = 4 dB :
4 = 10 log(1 + T/290) or
1 +T/290 = 10 ^ 0.4
1 + T/290 = 2.5119
T = 438 Kelvin

Then calculate receiver noise level:

No = -228.6 dBW + 10log(T)

Here -228.6 dBW is 10log(k) where k is Boltzmann’s constant 1.38 x 10^-23 J/K

No = -228.6 + 10log(438) = -202.18 dBW/Hz or -172.18 dBm/Hz
This about 2 dB lower than I previously had ( -170 dBm/Hz).

Furthermore if you reduce the noise figure from 4 dB to 1 dB you get more than a 3 db lowering of receiver noise level:
For NF = 1 dB, T = 75 Kelvin and No = -179.84 dBm/Hz.
So you get a 7 dB lower receiver noise level for that 3 db lower noise figure. Investing in an LNA is definitely a win!