# 101+ things to do with a LimeSDR

By using two directional antennas one pointing directly at existing RF source* and the other pointing in the opposite direction. As long as both captured IQ streams are phase coherent, which with the LimeSDR they should be since the same clock was used, then after initial calibration, the distance to a plane (or meteor trails) can be calculated. And the Doppler shift up or down would correspond to the approximate speed towards or away from the transmitter. It is a two dimensional Radar, you know the rough distance and approximate speed, but not the height or the angle.

*Terrestrial television stations (analogue/digital), Radio stations (FM, DAB, DRM+, HD-Radio), Mobile phone base stations, Satellites (GPS). The only real requirement is to use a wavelength at least an order of magnitude less than the size of the object.

To simplify, D1+D2 could be calculated by counting the number of samples that were required to shift back in time the signal at RX1 so that it was aligned with the weaker reflected signal at RX2. And dividing that distance by 2 would give the approximate distance to the plane (or a meteor trail).

If you were sampling at 20 MSPS (IQ) then each sample would be 50 nanoseconds in duration. And the distance than light in air can travel in 50 nanoseconds is ~14.9851 meters. So each sample in the offset would correspond to ~15 meters (~49 feet).

The above description is close to a Pulse-Doppler radar. But the configuration is probably closer to a monostatic radar in which the TX bandwidth is critical, for calculating the distance. If a single 100kHz bandwidth FM station was being used ( http://www.radartutorial.eu/01.basics/Range%20Resolution.en.html ) then minimum distance resolution would be 1.5km. The problem is that in the frequency domain you can not extract more information from a system than is in the system to begin with. So if there is only 100kHz of information you can not extract 20MHz of useful details.

One interesting side note is that the returned RF will be re-modulated by the vibrations on the surfaces of the aircraft, so at least in theory it should be possible to hear and distinguish, after proper processing, the downconverted audio returned by a helicopter, a propeller aircraft and a jet engine aircraft.

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18 ACARS (Aircraft Communications Addressing and Reporting System)
On paper with a LimeSDR, you could channelize the full 8MHz allocated around the world and decode all frames in parallel. ACARS squawks vary from 0.17 to 0.91 seconds in duration. The initial 0.0533 seconds of 128 bits set to 1 preamble, creates a 2400 Hz tone which makes ACARS transmissions easily recognisable with any AM receiver.

There is even a gr-acars2 block in Gnuradio which could be used, it reads in an AM signal and demodulates and decodes the ACARS messages.

…And likewise, you can also apply this to HFDL when tuned in the HF band and using the appropriate demod/decode for that medium, too - love that…!

de Marty, KN0CK

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By VNA is this what you mean : http://www.pa4tim.nl/?p=1594

Yes, pretty much - I got the idea from http://swigerco.com/gnuradio/ and was thinking of using gnuradio as the basis for it all and make it a little more “realtime”.

Frequency: 400 to 406 MHz
Frequency 1668.6 to 1689.8 MHz

Robert Bureau, who gave the name Radiosonde to his device, launched the very first one on the 7th of January 1929 in France. It returned precise encoded telemetry from its weather sensors.

Modern devices generally have a GPS receiver, temperature sensor, two pressure sensors, a humidity sensor and are launched several time a day all around the world to collect raw data during their accent for the global prediction of weather.

Individually they do not use much bandwidth (minimum of 200Hz, typically 20kHz and up to 1MHz), but the LimeSDR could monitor all frequencies at once in either band, but probably not both bands at the same time. And there is an open source project to demodulate a lot of Radiosondes (depending on the manufacturer, each uses their own protocol):

Here is a hardware teardown of a Vaisala RS92-SGP Radiosonde:

Geosynchronous phase 4 satellite coms and terrestrial microwave on SSB

See:

Interesting because then you could also create fingerprints for specific aircraft based on the audio.

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Do I read this right? Basically you are saying free hardware if you can find it? Or do they get tracked and retrieved?

This brings up another question. Once the balloon is released does it become ownerless? Like a ship abandoned at sea, it can then be claimed by anyone?

FWIW ascent

I have been inspired, here is my offering:

Lofted up into thin air
Sending data from everywhere
With the duty fulfilled and true
It went on flying but not right to you
You followed it with rf gear
It laid upon the field so clear
With the prize bragged about over beer

#22 (unless I lost track of the ordinality)

ADS-B (I have working in gnuradio) by 2020 all aircraft need to be equipped with ADS-B Out. This broadcasts lots of info depending on the configuration and other things. But at least you get ICAO Mode-S transponder number which is unique to each aircraft. Can also get speed/heading/lat/long/call sign and more. 1090MHz

ADS-R Are rebroadcasts from air-to-air and is somewhat new, this is interesting because it is essentially creating a mesh-network in the sky. This might also help eliminate bogies. i.e. bad actors tx ADS-B frames to make ghost planes appear.
Also at 1090MHz (I think)

FIS-B Is the free data that the FAA gives to planes equipped with ADS-B Out/In and that are also compliant hardware installation. Like a reward I guess. They give you wx radar info and other wx info as well as air traffic info. But I think this requires line-of-sight to the airfield.

UAT at 978MHz is allowed for aircraft flying under 18,000 ft. It is an alternative to ADS-B and sends data in a format that differs from ADS-B but most commerical aircraft can rx this and then tx it onto ADS-B via ADS-R. UAT is a lower cost way to
comply with the FARs for 2020 deadline (which may get extended). Apparently the FAA thinks that all aircraft owners have deep pockets but it’s not cheap to install
these devices.

There’s tons of stuff on github and there is even a VHDL decoder for ADS-B for bladerf.
dump1090 and dump978 are good search terms.

Most land in the sea, but the only thing that usually needs to be replaced to reuse them is the water activated battery (some countries have freepost addresses where people who find units can send them for reuse). But if you really want one, it would be easier to pick up an older models on ebay for ~\$20. Some people buy them just to chop off the GPS Quadrifilar Helix Antenna (L1 @ 1575.42 MHz and L2 @ 1227.60) which are wide band enough to work for Iridium (1618.85 to 1626.5 MHz) reception.

I may as well add another one:
23 Iridium reception (EDIT: You will need some filters and amplifiers as well e.g. a lorch 5df6-1675 [ will work, even though the signal is just outside the passband ] and a lna4all or similar devices).

## 24 Cell phone signal booster

The LimeSDR, if I understand correctly, can digitally clean up the signal before re-transmitting it again. It also has RSSI on the Rx’s which can be used to automatically adjust the gain so as not to annoy the network. I just need to work out how to program this thing!

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You mean a femtocell? Just to provide access indoors where signal is weak? Or you mean like the LimeSDR example on Hackaday (which was at the Lime guy’s house I think)?

Buying one would take all the fun out tracking one! I followed a link from one of those original links to a site (think it was deutsch) and the fellow there has tracked them down and has pictures.

I did a search for limeSDR on Hackaday - could not find much. Have you got the link @hTo137 ?
My project is a femtocell to [quote=“hTo137, post:32, topic:382, full:true”]
provide access indoors where signal is weak
[/quote] for which I’m building my own hardware. I’m going to use the LimeSDR as a spectrum analyser to see how well my gadget performs. Just got delivery of some really nice 4g band filers.
Ultimately, I’d like to take the project completely over to the LimeSDR platform, maybe just using the main chip, I don’t know yet. It’s early days!

Oh it’s on here:

numero veinte cinco or 25

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Yes I found this one just after it was published. There’s a couple of things missing in this tutorial - the duplex filters and the 4G_repeater.ini file. I found some filters, but the 4G_repeater.ini seems to have been erased from the interweb.

I also tried to contact the author but it seems he is no longer available - I’m guessing he came back from the future, wrote the tutorial and subsequently got abducted by aliens, as nobody in the Lime team seems to have any idea about his existence.

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I watched this some time ago but I thought I recalled mention of the repeater project. But it’s possible that the two are unrelated. I do not know who the presenter is there.

But maybe that would provide a clue?? As for the Band 20 Duplexers, are they typically an expensive part? I saw a homemade duplexer for 6m here:

https://ok2haz.ok2kld.cz/ok2haz/2015/10/ok0mf-6m-duplexer-development-and-construction/

From that I conclude they are big \$\$\$.