[Hackrf-dev] 1090 MHz

[Andrew Rich]

Question. I have a flightaware blue rtl dongle for adsb. It picks up aircraft some 100 kms away ok. But when I run it with a software defined radio I don't see great amplitudes . Why is that ? I would have expected to see quite large signal peaks on the sdr program . Is it because the signal is spread out over 2 MHz that I can see a distinct signal strength ? Does the signal need to be compressed down to a narrower bandwidth ?

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[Kevin Reid]

Post by Andrew Rich
Question. I have a flightaware blue rtl dongle for adsb. It picks up
aircraft some 100 kms away ok. But when I run it with a software defined
radio I don't see great amplitudes . Why is that ? I would have expected to
see quite large signal peaks on the sdr program . Is it because the signal
is spread out over 2 MHz that I can see a distinct signal strength ? Does
the signal need to be compressed down to a narrower bandwidth ?

These signals are extremely short in duration. Most SDR software does not
display all of the input signal in the waterfall, but samples it according
to the chosen display frame rate / scrolling speed, so any signal between
those samples will be missed. You need a rate much greater than 60 Hz to
consistently see these signals. (This does not mean you need a super-fast
monitor, just that the waterfall will scroll more than one row/pixel per
display frame.)

If you have gr-osmosdr and gr-fosphor installed, try:

osmocom_fft -F

and enter 1090M for frequency and 2.4M for sample rate. You should see
plenty of horizontal lines flying by, as gr-fosphor is designed to use and
display 100% of the input signal.

My own ShinySDR can also do high enough FFT rates and includes ADS-B
decoding.

[Andrew Rich]

Thank you Kevin

The data rate of sampling is 2MHz

I have a full install of gnu radio here perhaps I can play with some scope sinks ?

A

Sent from my iPhone

Post by Andrew Rich
Question. I have a flightaware blue rtl dongle for adsb. It picks up aircraft some 100 kms away ok. But when I run it with a software defined radio I don't see great amplitudes . Why is that ? I would have expected to see quite large signal peaks on the sdr program . Is it because the signal is spread out over 2 MHz that I can see a distinct signal strength ? Does the signal need to be compressed down to a narrower bandwidth ?

These signals are extremely short in duration. Most SDR software does not display all of the input signal in the waterfall, but samples it according to the chosen display frame rate / scrolling speed, so any signal between those samples will be missed. You need a rate much greater than 60 Hz to consistently see these signals. (This does not mean you need a super-fast monitor, just that the waterfall will scroll more than one row/pixel per display frame.)
osmocom_fft -F
and enter 1090M for frequency and 2.4M for sample rate. You should see plenty of horizontal lines flying by, as gr-fosphor is designed to use and display 100% of the input signal.
My own ShinySDR can also do high enough FFT rates and includes ADS-B decoding.

[Andrew Rich]

When I mentioned not being able to see distinct pulses

I was describing after recording in gqrx and then opening the file in inspectrum

My mission is to make an rtl-sdr based 1090 MHz 2 MHz oscilloscope type view showing transponder pulses

Like OOK on steroids

A

Sent from my iPhone

Post by Andrew Rich
Question. I have a flightaware blue rtl dongle for adsb. It picks up aircraft some 100 kms away ok. But when I run it with a software defined radio I don't see great amplitudes . Why is that ? I would have expected to see quite large signal peaks on the sdr program . Is it because the signal is spread out over 2 MHz that I can see a distinct signal strength ? Does the signal need to be compressed down to a narrower bandwidth ?

These signals are extremely short in duration. Most SDR software does not display all of the input signal in the waterfall, but samples it according to the chosen display frame rate / scrolling speed, so any signal between those samples will be missed. You need a rate much greater than 60 Hz to consistently see these signals. (This does not mean you need a super-fast monitor, just that the waterfall will scroll more than one row/pixel per display frame.)
osmocom_fft -F
and enter 1090M for frequency and 2.4M for sample rate. You should see plenty of horizontal lines flying by, as gr-fosphor is designed to use and display 100% of the input signal.
My own ShinySDR can also do high enough FFT rates and includes ADS-B decoding.

[Andrew Rich]

I am wondering if I can read the I and Q file with a script language such as perl and make a display

I have used perl and gd graph for this before

A

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Post by Kevin Reid
gr-fosphor