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Intro to Software Defined Radio – FM Stations and Tracking Aircraft

I have wanted to get viewing local aircraft via SDR going for a while after buying a pretty good RTLSDR unit with 27cm aerial and 3m RG174 coax lead from Ebay for £26 a while back. I screwed an iron washer to the roof so the magnet would stick, and it didn't blow off on a very windy day! (Yet...)

rtlsdr.png

aerial.png

If I'd known how easy it is to see aircraft by finding the right tutorials and not being pedantically stuck on using only SDR software that is in the linux repos (not much!), I'd have done it back in June.

For a background on SDR see:

Tracking planes for $20 or less

http://landoflinux.com/linux_sdr_adsb_gqrx_radio.html

Viewing aircraft similarly as on

https://www.flightradar24.com/ 

https://planefinder.net/

but for aircraft that only your SDR unit can receive, I found easiest by using dump1090 from github:

 git clone https://github.com/antirez/dump1090.git

Read the README, and if necessary install the missing files when the compile line complains:

cd dump1090

make

complaints..?

sudo apt-get install librtlsdr-dev libusb-1.0-0-dev

With those, make should compile the program now:

make

To run it and have the data overlaid via it's local http server on google maps, run:

sudo ./dump1090 --interactive --net --net-http-port 8080

or

sudo ./dump1090 --enable-agc --aggressive --net --net-http-port 8080

Try combos of those switches too, for max res and a table of planes in the terminal.

I found it complained about a default dvb driver that had hijacked the unit already so had to be blacklisted for next reboot in:

sudo vi /etc/modprobe.d/blacklist.conf

# snd_intel8x0m can interfere with snd_intel8x0, doesn't seem to support much
# hardware on its own (Ubuntu bug #2011, #6810)
blacklist snd_intel8x0m
blacklist dvb_usb_rtl28xxu

remove the module and try again:

sudo rmmod dvb_usb_rtl28xxu

sudo ./dump1090 --interactive --net --net-http-port 8080

This should now show any local aircraft info on the command line, so open a local (or remote) browser and view localhost:8080

screenshot-from-2016-09-24-161624.png

Once out of range for 60 secs it is removed from the table.

What amazed me the most was the distance that aircraft signals could be received over - about 60-80 miles or more! And on a cloudy wet day.

This depends on line of sight of course, as those planes out west from Cornwall aren't so blocked by hills from my location about 10 miles west of Truro on the map so pretty much clear to the sea out west. For scale, Plymouth is about 50 miles away from Truro.

There are projects for increasing the range using filters and tuned aerials for the 1090 MHz channel (UHF) that these signals are broadcast on. I may experiment now after this success, as I have a soldering iron...

Info on aircraft radio:

https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_Ch11.pdf

check p61 for ADBS info.

"ADS-B Collision avoidance is a significant part of the FAA’s NextGen plan for transforming the National Airspace System (NAS). Increasing the number of aircraft using the same quantity of airspace and ground facilities requires the implementation of new technologies to maintain a high level of performance and safety. The successful proliferation of global navigation satellite systems (GNSS), such as GPS, has led to the development of a collision avoidance system 11-61 ADS-B signal ADS-B signal Ground transceiver Conventional data networks GNSS position data Aircraft broadcast position, Altitude, Speed, etc. Figure 11-136. ADS-B OUT uses satellites to identify the position aircraft. This position is then broadcast to other aircraft and to ground stations along with other flight status information. Figure 11-135. Low power requirements allow remote ADS-B stations with only solar or propane support. This is not possible with ground radar due to high power demands which inhibit remote area radar coverage for air traffic purposes. known as automatic dependant surveillance broadcast (ADS-B). ADS-B is an integral part of NextGen program. The implementation of its ground and airborne infrastructure is currently underway. ADS-B is active in parts of the United States and around the world."

http://www.aviationpros.com/article/10389097/aircraft-communications

It would be nice to be able to hear audio transmissions too but these are on a range of frequencies dependent on civil aviation band usage e.g.

http://www.smeter.net/spectrum/aviation.php

http://www.jneuhaus.com/fccindex/aviation.html

Unless you live near an airport, you are unlikely to hear much chat anyway.

High Frequency Aviation Bands

Frequency BandAllocationSLC Receiver
Receivable
2850-
3155 kHz
Aviation (2850 to 3000 portion is MF)Yes
3400-
3500 kHz
Aviation SSB (3 KHz Channel spacing)Yes
4650-
4750 kHz
AviationYes
5450-
5730 kHz
Aviation SSB (3 KHz Channel spacing)Yes
6525-
6765 kHz
AviationYes

freqs.png

If you don't have an aerial, make one - this is a half wavelength aerial for resonance of a 27.5cm wave.

"As a result, an antenna that is half the
wavelength of the corresponding AC frequency is able to
allow full voltage and full current flow for the positive phase
of the AC signal in one direction. The negative phase of
the full AC sign wave is accommodated by the voltage and
current simply changing direction in the conductor. Thus, the
applied AC frequency flows through its entire wavelength,
first in one direction and then in the other. This produces the
strongest signal to be radiated by the transmitting antenna. It
also facilitates capture of the wave and maximum induced
voltage in the receiving antenna. For optimum performance, the
impedance of the transmission line should be equal to the
impedance of the antenna. In aviation antenna applications,
this is often approximately 50 ohms. 
"

halfwave.png

http://antirez.com/news/46

1090_antenna_1.png

c=fw

The Megas cancel so you get:

300 / 1090 = 0.275m or wavelength of 27.5cm. From below, the aerial needs to be less than 1/2 this to be tuned to this frequency.

Electrical solid earth wire should do, soldered to RG6 coax.

"A formula can be used to find the ideal length of a half
wavelength antenna required for a particular frequency as
follows: Antenna Length (feet) = 468 / F MHz. It takes into account the dielectric effect of the air at the end of an antenna that effectively shortens the length of the conductor required."

So that equation is saying that an aerial of length 0.429ft or 12.192cm is ok for 1090 MHz?

Just to give some distance perspective:

flights.png

41000ft  (highest I've seen yet) is 7.765 miles high (1760 yards in a mile, 3ft to a yard for the youngsters), and the furthest away on a clear day is about 150 miles away here, but you may not get full signal decodes:

150.png

You can also register with some sites to feed them data in return for their premium services, no registration fee or their professional software.

If you want more info on a plane, just google it's reg number or view it on one of the main flight tracker sites above e.g

IOS238

ios238.png

If you want to listen to FM radio on your SDR unit, install:

sudo apt-get install gqrx-sdr rtl-sdr

Run it and turn it on:

sudo gqrx

I found it complained about a default dvb driver that had hijacked the unit so had to be blacklisted on reboot in:

sudo vi /etc/modprobe.d/blacklist.conf

# snd_intel8x0m can interfere with snd_intel8x0, doesn't seem to support much
# hardware on its own (Ubuntu bug #2011, #6810)
blacklist snd_intel8x0m
blacklist dvb_usb_rtl28xxu

This allows gqrx to run the SDR unit - ignore the settings complaint, click no to edit - using the FM stereo dropdown I clearly picked up local radio:

107.png

And just to scare the shit out of you re the insecure future of this technology...!

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