How to simulate multipath signals?

[Baluncore]

"Assume 2 rx antennas are static in the same location.

There are things more fundamental than orientation of antennas.
How many receiver channels do you use ?
How are the antennas connected electrically ?
Please give us a diagram, a sketch or a photo of the antenna assembly.

 

[Nate Duong]

There are things more fundamental than orientation of antennas.
How many receiver channels do you use ?
How are the antennas connected electrically ?
Please give us a diagram, a sketch or a photo of the antenna assembly.

@ Baluncore : Sorry for the late response.
1. How many receiver channels do you use ?
I am still using the 2 RX channels.If possible, I will change the distance between 2 RX antennas to get the 1st null.

2. How are the antennas connected electrically ?
there are 2 antennas are connected electrically

3. Please give us a diagram, a sketch or a photo of the antenna assembly?
I do not have any diagram, everything now just use the theoretical to prove the existing of mutipath signal and delay. Everything now is just working on the Matlab and paper for the derivations and calculations and plots ... Since I understand the problem, the next step is going to work directly on the real data which are got from the SDR device.

So, what could I do in this case, Baluncore?

Thank you and very best regards,

Nate Duong.

 

[Baluncore]

First you must understand the instrumentation and the antenna array.

2. How are the antennas connected electrically ?
there are 2 antennas are connected electrically

But are the antennas connected toether, or is each antenna connected to a different receiver ?

3. Please give us a diagram, a sketch or a photo of the antenna assembly?
I do not have any diagram, everything now just use the theoretical to prove the existing of mutipath signal and delay.

Without some idea of your system configuration I cannot help you.

Since I understand the problem, the next step is going to work directly on the real data which are got from the SDR device.

So, what could I do in this case, Baluncore?

First you must understand the configuration of the instrumentation and the antenna array.
We still have absolutely no idea what your antenna array looks like. We are not able to read your mind or examine your equipment, so we can only give you help when you are able to communicate that information.

If you cannot identify the instrument configuration then you could use one antenna only with one receiver channel to record a time series of the down-converted signal. Then you could compute the autocorrelation of that data (with itself) to identify the repetition due to multi-path. The autocorrelation is quickly computed by using the FFT of the data, square that, then reverse the transform to get the time delays.
https://en.wikipedia.org/wiki/Autocorrelation

 

[Nate Duong]

First you must understand the instrumentation and the antenna array.But are the antennas connected toether, or is each antenna connected to a different receiver ?Without some idea of your system configuration I cannot help you.First you must understand the configuration of the instrumentation and the antenna array.
We still have absolutely no idea what your antenna array looks like. We are not able to read your mind or examine your equipment, so we can only give you help when you are able to communicate that information.

If you cannot identify the instrument configuration then you could use one antenna only with one receiver channel to record a time series of the down-converted signal. Then you could compute the autocorrelation of that data (with itself) to identify the repetition due to multi-path. The autocorrelation is quickly computed by using the FFT of the data, square that, then reverse the transform to get the time delays.
https://en.wikipedia.org/wiki/Autocorrelation

@ Baluncore : I understand my situation, this is more complicated when I keep asking you, I think you have your ideas, someone else have different ideas. As you said, we can use 1 rx antenna and follow this instruction from you. and I will try it.

Again, this is a signal from the digital tv transmitter or digital tv station, after collecting data and process with multipaths included, it will give us these plots for the phase and magnitude (look at the attached files with the name abs_original.jpg and phase_original.jpg)

Now, I am trying to assume there are no multipath or only 1 direct signal and 1 multipath. The observations and expectations are similar to the original (plots), from there I can see something and experience to detect multipath signal. Is it right? (you can look at my code file which is also attached).

the antennas which I am using, are < https://www.dxengineering.com/parts/dmn-srh815?seid=dxese1&cm_mmc=pla-google-_-shopping-_-dxese1-_-diamond-antenna&gclid=Cj0KEQiAnvfDBRCXrabLl6-6t-0BEiQAW4SRUHVgbNXzPhNr0FIcRXoX5OEACvSXVAoranPUOk_-yqYaAhCF8P8HAQ >

 

[Baluncore]

Is that 6" whip antenna vertical and mounted on a groundplane ?

 

[Nate Duong]

First you must understand the instrumentation and the antenna array.But are the antennas connected toether, or is each antenna connected to a different receiver ?Without some idea of your system configuration I cannot help you.First you must understand the configuration of the instrumentation and the antenna array.
We still have absolutely no idea what your antenna array looks like. We are not able to read your mind or examine your equipment, so we can only give you help when you are able to communicate that information.

If you cannot identify the instrument configuration then you could use one antenna only with one receiver channel to record a time series of the down-converted signal. Then you could compute the autocorrelation of that data (with itself) to identify the repetition due to multi-path. The autocorrelation is quickly computed by using the FFT of the data, square that, then reverse the transform to get the time delays.
https://en.wikipedia.org/wiki/Autocorrelation

I uploaded wrong code, here the one with updating.

 

[Nate Duong]

Is that 6" whip antenna vertical and mounted on a groundplane ?

@ Baluncore : I can say :"yes, this is"

 

[Baluncore]

@ Baluncore : I can say :"yes, this is"

If the short whip antenna is vertical on a ground plane, then it is a vertical dipole antenna.

3. Is it vertical or horizontal polarization?
ans:horizontal polarization

How do you justify using a vertically polarised antenna to receive a horizontally polarised signal ?

 

[Nate Duong]

If the short whip antenna is vertical on a ground plane, then it is a vertical dipole antenna.
How do you justify using a vertically polarised antenna to receive a horizontally polarised signal ?

@Baluncore : yes, you are right, this is a vertical dipole antenna.

We need to know 3 things: angle (alpha), delay(delta), amplitude(a) for any station.

The equation: mul = sum( an * exp(j(k*(x*cos(alpha) + y*sin(alpha)) - w*(t-delta)) which is justifed using a vertically polarised antenna to receive a horizontally polarised signal.

Since:
1. x is a center between 2 rx antennas, ( distance of 2 Rx is 10cm => x = 0.1/2 = 0.05 )
2. y : horizontal plane
3. z : vertical direction . For simple case z = 0 .

Mention: the equation is proved by derivation.

 

[Baluncore]

How do you justify using a vertically polarised antenna to receive a horizontally polarised signal ?

The equation: mul = sum( an * exp(j(k*(x*cos(alpha) + y*sin(alpha)) - w*(t-delta)) which is justifed using a vertically polarised antenna to receive a horizontally polarised signal.

I have done my time designing, building and operating radio surveillance equipment and antennas. I have been up to my elbows in radio astronomy and communications monitoring stations.

But I must admit, the justification you present here is a new one to me.
Maybe it is time for you to go back to your professor and ask for some help understanding signal polarisation.

 

[Nate Duong]

I have done my time designing, building and operating radio surveillance equipment and antennas. I have been up to my elbows in radio astronomy and communications monitoring stations.

But I must admit, the justification you present here is a new one to me.
Maybe it is time for you to go back to your professor and ask for some help understanding signal polarisation.

@Baluncore : so may ask you what is the the justification did you use?

I believe, they somehow will have similar theoretical. So I can understand what meaning of them.

 

[Baluncore]

http://www.air-stream.org.au/technical-references/antenna-polarisation

 

[sophiecentaur]

Could a reason for (apparently) cross polar reception be that many scattering / reflecting surfaces will re radiate a cross polar component. Signals received from the 'wrong' antenna could indicate the level of multipath signals. (Novel approach??)
A great multipath detection system that I have used it to look for AM on an FM carrier. (broadcast sound FM) Depth of AM tells you the level of the interfering signal. Displaying the carrier amplitude and frequency output from the demod on X and Y plates of a CRO gives you a diagonal line with a slope proportional to the proportion of multipath signal. It's a clever method but it only works for one particular mod system. (Though it could be used on the sound carrier of an analogue TV system too.

 

[Nate Duong]

http://www.air-stream.org.au/technical-references/antenna-polarisation

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