duncan crane

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About duncan crane

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  • Birthday 04/06/1947

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    Northampton, MA
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    radio science, sailing, family

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  1. 1. Here is my setup using the BNC adaptor and the external signal generator feeding channel 1 with nothing on channel 2. 2. Looking at WaveForms Scope I see 4 V p2p, at ~1 MHz on channel 1... 3. ... and due to crosstalk I see 50 mV p2p on channel 2. 4. Now I attach the short on channel 2 ... 5. And the crosstalk goes way down. 6. The testing with and without the short on channel 2 is informative and demonstrates well the existence of the crosstalk. But when I use the AD2 in my application I have signals coming in on channel 1 and 2 so of course I cannot short one out. You have answered my questions regarding the existence of crosstalk, as well as the possible option of using a second AD2 to eliminate crosstalk, which apparently is not an option for me because I would no longer see both signals in one WaveForm Scope window and therefore wouldn't have a synchronized view of both signals. So, I am going to see if there is some practical maximum level I can attenuate my signals down to that will reduce crosstalk to a level where it is no longer an issue. That might be 100 mV, maybe 50 mV, I shall see what I come up with. If I can do that on both channels without loosing the signals true phase shift I am in business. Stay tuned!
  2. Thanks for the detailed response Atilla. I duplicated your tests to make sure I understood what you were saying and to verify my AD2 is working properly. Screen shots attached. I used an external signal generator for all my tests rather than the built-in signal generator in Wavegen. You did not get significant crosstalk using an external signal generator but I did. Shorting out the other channel helped a little when I was NOT using the BNC adaptor and it really helped a lot when I WAS using the adaptor. So our test results were similar. It is interesting to note that when feeding these test signals or other signals coming in off my two antennas directly into my old analog oscilloscope there is never any hint of crosstalk. So bottom line is yes, my device is working as advertised; and yes there will be crosstalk occurring within the AD2 device. I do not believe any of the crosstalk I am seeing is coming from external wires or cables. My particular application is all about phase difference between the two signals I am bringing in on the 2 analog channels of the AD2. Both signals will be the same frequency and at times one or both of them may be as strong as a volt or more. Any crosstalk will throw off my measurements of phase difference in a big way. As I think about it, the only way that I can go forward using the AD2 would be to purchase a second one and run my signals through separate AD2 devices. Some questions: 1. Will I be able to display all four channels in a single Scope window? 2. Can I click a Single sampling and get readings on all four channels, synchronized readings? 3. Is it reasonable to assume that this approach will eliminate any AD2 device originated crosstalk? Thanks for your excellent support Atilla! Duncan Crosstalk.docx
  3. atilla, Sorry for the delay in response to your feedback. I have been out of action with the flu and in fact am still a little light headed. I think I understand what you are saying and have come up with a way to measure any random delay introduced by the two AD2 channels and subsequent Math Filtering. I have two 10 ft long straight wire antennas stretched across my living room ceiling, mounted with insulators at each end. (My wife just loves them. Not.) Using these two antennas as inputs to channels 1 and 2 on the AD2, I set the Math Filters on both to 560 KHz (near the low end of the AM dial). Then with triggering turned off I sampled one shot at a time. What I got was a consistent pattern of the two channels being fully in step. No phase shift. The signals jump to a new location each time I sample but they jump together. This is good. Then I did the same thing at a point higher on the AM dial: 1.4 MHz. I got the same consistent results. So for my purposes, the AD2 is capturing two signals at the same point in time and then allowing me to apply a Math Filter to each signal to pull out the one carrier frequency of interest, all without losing the relative timing of the signals from when they first hit my antennas. This is very good. My confidence in the AD2 is now very high and I feel that I can use it to work out what is happening with my experimental antennas. Thanks, I will be in touch. Duncan
  4. I know I have a lot to learn about this device and plan to work through the conversations on the Forum and the many YouTube videos out there. Please point me to any especially informative sources that you think I would benefit from. You have got me thinking in a slightly different direction. I have been talking about "triggering" but maybe I don't need triggering in the classical sense. I like the way I can hit the Single button on the scope and capture a few cycles of my signals on the two channels. I don't need a repeating sweep, just one capture gives me what I need. And I don't care exactly when the capture started or at what point on the signal's upward or downward voltage swing the capture started. What I do care about is that the capture on both channels starts at exactly the same time. So that when I look at the two signals displayed on the scope I know that I am seeing when in time the two signals occurred in relation to each other down to a precision of a few nanoseconds. Was channel 1 ahead of channel 2 by 100 nanoseconds or visa versa? So maybe a Manual trigger is good enough for what I am doing. But after the two signals are captured I need to apply that Math Filter to each of them to narrow the signal down to the one AM broadcast channel. Would you expect the filtering process to introduce random delays or phase shifts between the two channels so that the original timing between the two signals is lost? I shall study on.
  5. atilla, I purchased my AD2. Love it. Here is what I am seeing using your suggestion of a Math filter. This is a lovely picture of the 1.4 MHz carrier from my local AM broadcast station WHMP. However, the triggering is not right. Every time I do a Single capture I get this same picture but it crosses the 0 sec vertical at a different voltage. I am guessing that this is because the source of my trigger is Channel 1 which naturally contains all kinds of overlapping signals coming in from my antenna. So the Rising 0 volt point of Channel 1 will not necessarily line up with the Rising 0 volt point of the output from the filter. I think what I really need for a trigger source is the output of the Filter not the input. Can this be done? I don't see an option for this in the Scope Trigger settings. I checked out the SDK examples and I didn't see an example of using the output of a Scope Math Filter as the source of the trigger but I am not skilled in these programming languages. Any thoughts?
  6. Atilla, What you are showing with the Math Filter in WaveForms looks exactly like what I am looking for! Very exciting. Just to be clear, in your example the input comes in on one of the Analog Discovery 2 channels and is fed to a Math Filter routine in WaveForms. The output of the filter (in brown) is in the time domain and shows the original pre-sampled carrier wave form? So did the filter do a reverse FFT on the sampled spectrum? How precise can I get this picture? Can I see just a couple of cycles of the original AM carrier and be confident of where in time a given cycle starts as compared to a similar AM carrier signal coming in on the second Analog Discovery 2 channel? That is to say, could I see a few degrees of phase shift between the two original AM signals? Assume that we are talking about a 1 meg Hz AM broadcast signal coming in on two different antennas to the two Analog Discovery 2 channels. I assume the two AD2 channels are synced. Duncan
  7. I saw the Matlab option but have to admit I was scared off a little by all that I do not know. Maybe I should jump into it. Thanks X.
  8. I would like to use the Analog Discovery 2 to look at the carrier signal coming in from an AM broadcast station. To do this I would need to tune or filter the many signals coming in on my antenna down to one station of interest. I am thinking that this type of tuning is not something that the AD2 can do. Is this correct? Does anyone know of a simple device that can act as a front end to the AD2 to tune and perhaps amplify the signal in this way? I have looked into SDR's that are very focused on doing just this but I am not seeing how I can extract the carrier signal before it goes to mixing and demodulation.