ADS-B SIGNAL ON AN OSCILLOSCOPE

[chapi]

Anyone can guide me on how to get a receiver like in this video:

So I'll be able to watch an ADS-B signal on a scope?

Also if possible to watch signals from GPS satellites or any other rf source 300 miles far or more with a 10ns accuracy.

Thanks.

 

[Token]

The receiver is a TRF, it uses a couple of SAW filters to define the bandwidth to be detected, an LNA to bump the signals up between the first and second filters, and all of that is fed into a log detector. The receiver is going to turn anything within the passband of the SAW filters into video that can be displayed on a scope. You will have no indication of the frequency of a specific signal, if it is in the passband you will see it. There is not a kit or anything you can buy to build this, you would have to scratch build it yourself.

I have given this zero thought as to how useful it might be, but you could probably build the same thing out of eval boards or something similar. For sure the amp ( https://www.amazon.com/FORIOT-Frequency-Wideband-Amplifier-0-1-2000MHz/dp/B0CFLB7QLF/ ) and logdet ( https://www.amazon.com/0-1-2-5GHz-Logarithmic-Amplifiers-Controller-Measurement/dp/B08KS1L4FX ) can be had on boards, I assume you can find the filters also ( https://www.amazon.com/1090MHz-Interface-Interference-Electronic-Components/dp/B0CG6FSJ52/ ). If you want to do GPS, change the filters to GPS freqs ( https://www.amazon.com/Bandpass-Receiver-Characteristic-Impedance-Positioning/dp/B0CH79S1K9/ ) and that will probably get there.

But really, you could do it all with an SDR also. As long as you can ship the I/Q bandwidth wide enough for the data from the SDR to a computer based oscope program you would be good to go to display the pulses.

Not sure what you mean by "Also if possible to watch signals from GPS satellites or any other rf source 300 miles far or more with a 10ns accuracy." Nothing in the way of receive hardware can guarantee range, there is too much external of the receiver you need to consider to model range. In addition to the specific transmitted signal launch power, the antenna(s) height, topography, etc, are going to factor in. Not sure how a timing accuracy spec enters into this. Are you trying to use this as a core module of a TDOA solution or something? The analog version above (not the SDR based solution) will have minimal latency, and what latency it does have can be characterized and backed out.

T!

 

[chapi]

Thanks so much for your reply.

I am trying to build a device that will receive a signal from a known source of rf with 2 antennas that are connected to 2 separate receivers which are connected to channels A and B of a scope, and thus find the TDOA of the signal, in our case the ADS-B signal, but can be a signal from any other distanced rf source.

The idea is that When I watch the waveform of the signal on each channel on the scope, I will see 2 identical waveforms and if I move one antenna toward or away from the rf source, the waveform on the scope which is associated with this antenna will move instantly 3 ns for every meter I move the antenna.

 

[Token]

I am trying to build a device that will receive a signal from a known source of rf with 2 antennas that are connected to 2 separate receivers which are connected to channels A and B of a scope, and thus find the TDOA of the signal, in our case the ADS-B signal, but can be a signal from any other distanced rf source.

The idea is that When I watch the waveform of the signal on each channel on the scope, I will see 2 identical waveforms and if I move one antenna toward or away from the rf source, the waveform on the scope which is associated with this antenna will move instantly 3 ns for every meter I move the antenna.

OK, I can see how the thought process plays out. And it would certainly be fun to play with. Don't take the below as discouragement on what you are trying, I am just thinking out loud below.

I suspect you will find too much variability (both time and amplitude) in detection of an open air signal to be looking for 3 ns deltas in time. i.e the signal strength on each receiver for a given real world, open air, source will have at least small, and probably unpredictable, differences in amplitude. That will possibly lead to different shapes on the leading edge of the pulse at any given trigger point, which will lead to timing variances. Or there will be multipath that smears the data greater than 3 ns. etc.

And then, in densely used spectrum like 1090 MHz, how do you correlate pulses or groups of pulses to the same target? Sure, when you grab a single pulse or triggered event then the two pulses, one from detector A and the other from detector B, it should be very easy to correlate. But you are talking about capturing a pulse, comparing timing, and then moving an antenna and doing it again. The next pulse you grab, is it from the same target source, or a different one? If you demodulate the data (I don't think you can do that with the TRF described) then you can correlate pulse packets to a source, and then possibly pulse timing to the source.

T!

 

[chapi]

Thanks Token, I ordered all the components you suggested from Amazon, I'll wait few days and will try to see if I can get any meaningful results.

The distance to the rf source is a key factor for my project. As far as better. Naturally, if I can show a GPS signal waveform on the scope it will be ideal, or even better from a geostationary satellite. I tried it with XM satellites but was unsuccessful. WWV also could be an option, even though what I'll get is probably a multipath, let alone the sky waves.

Even Noaa satellites may work, but the Audio signals are too wide since I need a nanoseconds accuracy. If you may think of any distanced satellite that would yield the waveform on my scope like in the video, or any other method to compare the TDOA from the 2 antennas, that would do.

 

[merlin]

I see what you have in mind. LoJac receivers use the same principal, measuring the difference in time between two (to 4) antennas.
The delta phase can be measured but timing may need to be less than a nanosecond.
A GPSDO can give accurate timing to trigger your scope then view the phase between two receivers.
Just how critical this will be is the feed lines from antenna will have to be exactly the same length, signal lines from the receivers must be exactly the same length to scope inputs. any mismatch in propagation delays will give you eronious results.
All of this theory falls into the category of RDF and consider with digital (ads b) down to 1 Ns.
If you have a 4 channel scope, you can look at the GPSDO outputs (1PPS or 10MHz) and trigger the scope from that channel.

 

[dlwtrunked]

Thanks so much for your reply.

I am trying to build a device that will receive a signal from a known source of rf with 2 antennas that are connected to 2 separate receivers which are connected to channels A and B of a scope, and thus find the TDOA of the signal, in our case the ADS-B signal, but can be a signal from any other distanced rf source.

The idea is that When I watch the waveform of the signal on each channel on the scope, I will see 2 identical waveforms and if I move one antenna toward or away from the rf source, the waveform on the scope which is associated with this antenna will move instantly 3 ns for every meter I move the antenna.

You mayfind reflections from nearby objects causing you problems with what you are attempting.

 

[chapi]

Thanks merlin.

Will I be able to compare the toa of the gps signal to 2 antennas with few ns accuracy on the scope if I’ll use 2 GPSOD connected to channels A and B of the scope? Is there any other method to do it?

And another question: Is there a way I can compare gps satellite time or UTC which arrives to 2 antennas distanced 2 meter with few ns accuracy? If so, what equipment and what apparatus should I use? Is there a device which will show the UTC in ns accuracy like a clock does?

 

[chapi]

Another question:

If I would like to view the carrier wave of 520mhz for example on a scope, similar to the way it was done in the video. How can I do it?

If for example I’ll transmit with a directional antenna to a receiver 100 miles away, or simply try to view the carrier wave of a distanced radio station on my scope, how can it be done and what equipment should I use?

I was able to do it with a crystal radio and a near by am station, but was not successful with distanced fm stations.

Like before, the key is that the wave form on channel B on the scope will be moved 1ns for every foot I’ll move the associated receiver’s antenna.

Thanks.

 

[Token]

Another question:

If I would like to view the carrier wave of 520mhz for example on a scope, similar to the way it was done in the video. How can I do it?

If for example I’ll transmit with a directional antenna to a receiver 100 miles away, or simply try to view the carrier wave of a distanced radio station on my scope, how can it be done and what equipment should I use?

I was able to do it with a crystal radio and a near by am station, but was not successful with distanced fm stations.

Like before, the key is that the wave form on channel B on the scope will be moved 1ns for every foot I’ll move the associated receiver’s antenna.

I am a little confused about what you are asking / saying, or maybe you do not have a complete understanding. You are talking about “viewing the carrier wave”, “similar to the way it was done on the video”. But, the video does not show anything to do with the carrier at all, the video is not viewing or displaying the carrier, it only shows the data, as detected video, originally modulated on the carrier and completely strips the carrier out.

To view the carrier wave of a signal at 520 MHz you could use an oscope with a bandwidth greater than the signal being observed. i.e. you could use a 1 GHz scope to directly view a 520 MHz carrier.

To view the carrier of a distant radio transmission on an oscope, assuming the oscope has the bandwidth necessary to display the signal, attach the antenna directly to the oscope. Of course, the signal needs to have enough amplitude to be detectable on the scope.

But the question here becomes, are you actually trying to view the carrier, or rather are you trying to view the data on the carrier? More importantly, what is your end goal, what are you trying to do? Are you just trying to show propagation delay? Or are you actually trying to determine direction of a source? Is this a school project, or just something you are messing with?

T!

 

[chapi]

Thanks Token.

Viewing the data modulated on the wave with a scope like in the video in few ns accuracy is ideal, 2nd best is viewing the carrier wave which is obviously in ns accuracy.

I can easily do it with a transmitter few meters from the scope, but how can I do it from 100 km away? How can I view for example the carrier wave of radio station transmitting on 101.1 MHz fm from 100 km? What equipment should I use?

I was able to do it with a crystal radio from an am station 10 km far, but I need much farther distance to this project, a relativistic physics project.

 

[krokus]

What is the transmitter power? If it is a low power signal, you would need an elevated antenna. If it is a broadcast strength signal, then a small antenna should do. You would want a tuned circuit for just the signal you want to receive. If that is the 101.1 MHz, you could use broadcast receiver, and monitor the output of that, or the IF going into the demodulator.

 

[chapi]

Thanks, but how would I separate the desired 101.1 mhz transmission?

Suppose I use a baofeng transmitter and transmit on 501 mhz. I would like to view the transmitted signal waveform from 20 km distance on a scope so if I turn off the transmitter, the wave form will disappear from the scope. What equipment should I use? I am able to do it with a crystal radio and local near by am stations.

The basic idea is to compare a toa of a signal to 2 antennas from as far as possible.

 

[krokus]

Thanks, but how would I separate the desired 101.1 mhz transmission

Separate it from what?

 

[chapi]

From all the other transmissions that the antenna receives.

How would I display only the 101.1 mhz from a distanced radio station on the scope? What equipment should I use, band pass?

Connecting the antenna to the scope will display only the near by strong stations, not the one I need.

 

[krokus]

From all the other transmissions that the antenna receives.

How would I display only the 101.1 mhz from a distanced radio station on the scope? What equipment should I use, band pass?

Connecting the antenna to the scope will display only the near by strong stations, not the one I need.

That would be using the tuned circuit, I mentioned previously.

 

[chapi]

Thanks, I was able to get the waveform on the scope from 10 km away am station with a crystal radio, but do you know maybe where to get a tuned circuit which will be able to show the waveform from 100-500 mhz station 100 km far? Could not find tuned circuits on Amazon or else ware..

Do I need an amplifier?

 

[krokus]

Thanks, I was able to get the waveform on the scope from 10 km away am station with a crystal radio, but do you know maybe where to get a tuned circuit which will be able to show the waveform from 100-500 mhz station 100 km far? Could not find tuned circuits on Amazon or else ware..

Do I need an amplifier?

Probably easier to use SDR equipment, that is then coupled to oscilloscope software.

The 100km could present a problem, as previously mentioned. Depends on antenna height at both ends, any blocking by the Earth or buildings, transmit power, antenna gain, localized interference, etc.

 

[merlin]

Thanks Token.

Viewing the data modulated on the wave with a scope like in the video in few ns accuracy is ideal, 2nd best is viewing the carrier wave which is obviously in ns accuracy.

I can easily do it with a transmitter few meters from the scope, but how can I do it from 100 km away? How can I view for example the carrier wave of radio station transmitting on 101.1 MHz fm from 100 km? What equipment should I use?

I was able to do it with a crystal radio from an am station 10 km far, but I need much farther distance to this project, a relativistic physics project.

At 500 + MHz, it just not possible without 10 Megawatt transmitter. If you can receive a BC station @ 101 MHz and 100 Km, you should be able to see that on a scope. the scope would have to be capable of seeing over 100 MHz, or you would have to tap a receiver after the first IF.
What you are talking is far from a crytal receiver and local AM BC.

 

[chapi]

Thanks guys, I’m in l a, a lot of stations and one is interesting in particular which transmits at 494.325 MHz cw from mount Wilson and can be received easily from 200 km.

What I’m trying to do is to compare the toa of a signal in few ns accuracy to 2 antennas from as far as possible, preferably satellites like gps communication or weather satellites like noaa. As far as possible, but relatively close sources like radio stations is possible to work with too if no other source is available.

A modulated signal like in the adsb video is preferred since it’s a clear cut and easy to work with, and second best is the waveform itself.

Another thing is that one of the antennas is moving fast by rotation, and I need another channel for triggering so I’m not sure how a pc based scope would do.

Merlin, you mentioned Gpsdo. Can you think maybe of any device that will be able to do what I want? Simply comparing the pps from 2 gps devices won’t do because of the latency, it should be instantaneous.