More on Showing wave form on an oscilloscope.

Main forum to discuss RTL-SDR related topics.
Post Reply
snuz2001
Posts: 11
Joined: Mon Aug 26, 2019 6:40 am

More on Showing wave form on an oscilloscope.

Post by snuz2001 » Sun Oct 13, 2019 8:21 am

1. what is a "full-duplex SDR to downsample"? where do I get it?

2. "You can use narrow bandpass filter and about 80 dB amplifier in order to get it visible on oscilloscope".

How technically can I use it to view a 500 mile far radio source (Noaa transmitter) on my scope? what receiver should I use? Can I use a simple receiver like a baofeng?

3 "The easy solution would be to use a receiver with sufficient bandwidth and sensitivity and connect an IF-output"

What is an IF output? where do I get it and where do I connect it to the receiver?
Do you know any receivers which comes with an rf or IF output so I can connect it directly to the scope and view Noaa's 137.1 Mhz carrier wave?

4. I read a lot about TOA and TDOA with sdr. Is there any way I can compare the arrival time of a distanced signal (like Noaa's) to 2 different antennas with around 50 ns accuracy? if so, how technically it can be done (what equipment, connections, etc.)

snn47
Posts: 192
Joined: Tue Dec 27, 2016 11:00 pm

Re: More on Showing wave form on an oscilloscope.

Post by snn47 » Mon Oct 14, 2019 1:07 pm

IF-Output this question is easy to answer:

Before SDR were becoming reasonably priced, almost all receiver used conversion of the RF signal to a lower Intermediate Frequencies (IF’s).

IF receiver were standard, whenever amplification of weak signals with reasonably noise figures and use of (very) narrow filter could not be done on the transmit frequencies itself.
BC- and VHF HAM-Radios used down-conversion to IF of 10.7 MHz or 9 MHz (21.4 MHz less common). For CW the required filter bandwidth of a few 100 Hz wide filter was expensive but possible. In cheaper receiver often a second IF around 455 kHz was used to allow use of much cheaper LC or ceramic filter.

Spectrum analyzer and oscilloscopes were also expensive and limited to a max. of 10 or 20 MHz, nor did they provide the necessary sensitivity and selectivity. The signals on the IF were already strong enough to be display and were provided via a buffer amplifier to an IF-Output which allowed to connect oscilloscopes, panorama receiver or additional decoders.
4. I read a lot about TOA and TDOA with sdr. Is there any way I can compare the arrival time of a distanced signal (like Noaa's) to 2 different antennas with around 50 ns accuracy? if so, how technically it can be done (what equipment, connections, etc.)
If you want to not only receive and decode/display signals, but compare time of arrival, you will have to calibrate your receive setup to ensure that time delay from the antenna and used coax cable and processing time in the receiver are identical or you calibrate and compensate your setup.

snuz2001
Posts: 11
Joined: Mon Aug 26, 2019 6:40 am

Re: More on Showing wave form on an oscilloscope.

Post by snuz2001 » Tue Oct 15, 2019 7:46 am

Thanks so much for the reply.

What will really help me is a technical explanation of how it should be done - where to connect the scope to the receiver, how to connect the computer with the sdr to a scope or any other way I will be able to compare the arrival time of a signal to 2 antennas.

The ideal is a situation where if I move one antenna 10 m away from the transmitter who is 1000 km away, the signal from this antenna will be delayed 30 ns because of the speed of light, and I'll be able to view the difference either on my scope, a computer, or any other device.

It is done indirectly in simple devices of tdoa like this:

https://www.youtube.com/watch?v=JVGf28ckHyg

I was able to use this simple device on Noaa satellites 1500 km away.

But I need the direct way - being able to see the tdoa of the signal in ns to the 2 antennas.

alanzfq
Posts: 66
Joined: Thu Oct 04, 2018 11:18 am

Re: More on Showing wave form on an oscilloscope.

Post by alanzfq » Tue Oct 15, 2019 8:16 am

The youtube shows a simple way of getting an equal distance.
Measuring between antennas is not simple.
I can not give you instructions but I think you will need two identical locked receivers and then compare the outputs.
I do not know where to take the output to be able to preserve and observe or measure the tiny time difference. Nano seconds using a scope does not seem easy, can you do that for a start?
This is a specialised subject searching elsewhere may be more productive.

Alan

snuz2001
Posts: 11
Joined: Mon Aug 26, 2019 6:40 am

Re: More on Showing wave form on an oscilloscope.

Post by snuz2001 » Tue Oct 15, 2019 8:49 am

Thanks Alan, the scope is the easy part if I knew where to get the rf signal from. see:

https://www.youtube.com/watch?v=L6YJqhbsuFY&t=92s

here he shows a way to measure the tdoa on the scope. The question is where does he gets the signal from? how he does it?

You may do it with a crystal radio:

https://www.youtube.com/watch?v=2f2nQ9yDAIA

but I need a 1000 km far signal, crystal radio would not get it.

alanzfq
Posts: 66
Joined: Thu Oct 04, 2018 11:18 am

Re: More on Showing wave form on an oscilloscope.

Post by alanzfq » Wed Oct 16, 2019 6:41 am

Presumably that software will compare two audio signals from the two synchronised receivers?
Alan

snuz2001
Posts: 11
Joined: Mon Aug 26, 2019 6:40 am

Re: More on Showing wave form on an oscilloscope.

Post by snuz2001 » Wed Oct 16, 2019 8:06 am

Looks like audio, but could be any signal I believe, rf carrier signal too.

Notice that the simple device for direction finding:

https://www.ebay.com/itm/RAINBOWKITS-SD ... 1436!US!-1

automatically compare the tdoa of a radio signal in a ns accuracy, even from 1000 km, but does not displays it on a screen which is what I want.

alanzfq
Posts: 66
Joined: Thu Oct 04, 2018 11:18 am

Re: More on Showing wave form on an oscilloscope.

Post by alanzfq » Wed Oct 16, 2019 9:14 am

"could be any signal I believe" Not fed into a soundcard.
If you do not use that method I think it is even more complicated.
Measurement is the problem.
Alan

snuz2001
Posts: 11
Joined: Mon Aug 26, 2019 6:40 am

Re: More on Showing wave form on an oscilloscope.

Post by snuz2001 » Thu Oct 17, 2019 10:25 am

Audio signal would not help, I need 50 ns accuracy and audio is in micro seconds.

Post Reply