ADSB MLAT frequency

[hruskacha]

I have an Airspy R2 and software called ADSBspy for tracking aircraft. There is a setting called "mlat_freq" and it has "10, 20, 24MHz" options. What is this? I know what MLAT is and how it works, but what does the frequency have to do with it? Those seem like bandwidths not actual frequencies.

The software is quite old, so I couldn't find much. But it is the best for Airspy.

 

[merlin]

Those are bandwidths.

 

[hruskacha]

Those are bandwidths.

I understand that, but what does bandwidth have to do with MLAT? MLAT uses time difference (TDOA) of ModeS/ADS-B signals on known frequencies (1030MHz for Interrogation, 1090MHz for Reply) from multiple receivers. If the frequencies are known, Why would they have bandwidth options? Also note that only ONE of those bandwidth options is valid for Airspy R2 (which has the highest bandwidth of any airspy product). The Airspy R2 has a max bandwidth of 10MHz, but 20 and 24MHz are listed... Does that mean its hopping frequencies or trying to span that range? I tried looking up technical documentation for MLAT, but I cant find anything relating to receiver bandwidth.

ADS-B on 1090MHz has 2MHz bandwidth, and UAT on 978MHz has a bandwidth of ~1.3MHz.

 

[merlin]

Bandwidth is the bandpass of the last IF. No frequency hopping. You can narrow your R2 down to 2 MHz and get the full bandwidth of ADS-B.
It is digital and ocupies that 2 MHz segment with a center frequency of 1090 or 1030 MHz.
That signal feeds a DSP that decodes and parses the data stream. Now you have raw I/Q data. That piped into an ADS-B decoder, you see all the different information.
This is what ADS-B looks like on your 2 MHz wide R2 signal and waterfall.
MLAT is Multilateration in the horizontal plane. Basically, the separation of aircraft.

 

[morfis]

..., but what does bandwidth have to do with MLAT?

It doesn't...it's meaningless waffle by whoever wrote the webpage (and inbuilt help text of adsbspy).
Multilateration is mathematics to calculate the spatial position of a transmission origin based on time of arrival of the that signal at multiple antennas (which for the useage here is remote sites, each with it's own receiver not just different antennas) as you say.

As for whether adsbspy is "the best for Airspy" I doubt it but Yousef is always going to claim his software is the best.