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Re: TV on a 7000 Scope - impossible on any other lab scope
PA4TIM
That is a great video. How do you do that. I found out the film itself also on youtube and seems to be is original clip from that song. So he feeds the video signal ( composite ? ) to the scope. Coult be a job for a raspberry pi. Fred PA4TIM
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Re: Impossible Photo except on a 7000 scope
Mark Wendt <mark.wendt@...>
Yeah, Don mentioned that too. See my previous post on Ebay's lousy search. ;-)
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Mark
On 06/05/2013 08:09 AM, Dave Daniel wrote:
Thanks.
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Re: Impossible Photo except on a 7000 scope
Mark Wendt <mark.wendt@...>
Well, that's very strange. I didn't look that close at the listings, but those were what turned up on a search for "Tektronix 7J20". Looks like Ebay's search has gotten even worse than what we discussed previously.
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Mark
On 06/05/2013 07:58 AM, Don Black wrote:
Sadly, re-read the type. They are all 7D20s.
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Re: Impossible Photo except on a 7000 scope
Dave Daniel
Thanks.
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Those are 7D20s, not 7J20s. DaveD
On 6/5/2013 5:54 AM, Mark Wendt wrote:
On 06/05/2013 07:50 AM, Dave Daniel wrote:I see three 7D20s, but no 7J20s.Dave,
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Re: Impossible Photo except on a 7000 scope
Don Black <donald_black@...>
Sadly, re-read the type. They are all 7D20s.
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Don Black.
On 05-Jun-13 9:54 PM, Mark Wendt wrote:
On 06/05/2013 07:50 AM, Dave Daniel wrote:I see three 7D20s, but no 7J20s.Dave,
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Re: Impossible Photo except on a 7000 scope
Mark Wendt <mark.wendt@...>
On 06/05/2013 07:50 AM, Dave Daniel wrote:
I see three 7D20s, but no 7J20s.Dave, Ebay item #'s 360442801904, 390586622614, and 130922343379. Mark
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Re: Impossible Photo except on a 7000 scope
Dave Daniel
I see three 7D20s, but no 7J20s.
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Can you post the listing URLs for the 7J20s? Thanks DaveD
On 6/5/2013 3:33 AM, Mark Wendt wrote:
On 06/04/2013 07:51 PM, Dennis Tillman wrote:Hi Larry,Dennis,
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Re: TV on a 7000 Scope - impossible on any other lab scope
I guess you may have already seen this, but it's one of my all-time favourites. (Good music as well).
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http://www.youtube.com/watch?v=6Ac1G_5N73g John
--- In TekScopes@yahoogroups.com, "Dennis Tillman" <dennis@...> wrote:
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Re: Impossible Photo except on a 7000 scope
Mark Wendt <mark.wendt@...>
On 06/04/2013 07:51 PM, Dennis Tillman wrote:
Hi Larry,Dennis, Your timing, as usual, is impeccable. There are currently three 7J20's up for auction on Ebay right not. ;-) Mark
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Re: TV on a 7000 Scope - impossible on any other lab scope
The scopes I aw in TV shops in the mid '60 were free running, and very few would do 500 KHz. Several shop owners laughed when I bought a new Leader LBO-505 in the early '70s and told me scopes were a waste of money.
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Dennis Tillman wrote:
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Re: TV on a 7000 Scope - impossible on any other lab scope
Right. When I worked at a TV store in my youth we could tell when the
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vertical sync tube was shot because the vertical would roll slowly at 60Hz. Dennis
-----Original Message-----
From: Michael A. Terrell, Sent: Wednesday, June 05, 2013 12:36 AM NTSC video is 59.94 Hz vertical and 15,734.34 Hz Horizontal. I used to watch TV by feeding the video output of an old Polarad SA into an amber computer monitor. Just for fun, I let it slowly sweep all the TV channels on the CATV system and would ask the KNAs to explain what it was doing. ;-)
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Re: TV on a 7000 Scope - impossible on any other lab scope
Dennis Tillman wrote:
NTSC video is 59.94 Hz vertical and 15,734.34 Hz Horizontal. I used to watch TV by feeding the video output of an old Polarad SA into an amber computer monitor. Just for fun, I let it slowly sweep all the TV channels on the CATV system and would ask the KNAs to explain what it was doing. ;-)
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Re: TV on a 7000 Scope - impossible on any other lab scope
I don’t recall how the physics professor had his 7834 set up to display the Portland analog TV signal. I had to use a work around because I didn’t have a corresponding TV signal to use. As a result my setup was more complex and finicky than his.
The 7L12 resolution was set to 3MHz to correspond to the bandwidth of the video signal being transmitted. The Frequency Span/Div was set to 1KHz/Div which was the same as the sweep speed of the 7B70 in the left vertical slot. Both the 7B70 and the 7L12 were sync’d to 60Hz so they were sweeping synchronously. 60Hz is coincidentally very close to the actual vertical sync frequency of an analog TV signal. This coincidence is important. I do not know what the horizontal sync frequency is for the wireless camera I was using but I think it was close to 60Hz. The 7B92 was free running at 10uSec/Div in the far right horizontal slot. Up to this point I borrowed what I saw down in Portland. A lot of creative thinking was necessary on the part of someone to realize this could be done and to have figured out everything so far.
Where I had to improvise was by connecting the Vert Out signal from the 7L12 (on a front panel pin jack) to the Z axis input of the scope to modulate the intensity. Since the amplitude of the video signal is proportional to the brightness of the image (or inversely proportional, I forget) it modulates the brightness of the CRT showing the image of what is being transmitted by the wireless camera.
The final step was to capture a photograph of the CRT which I did with my HoodWink Scope camera.
Next time I am in Portland I will refine the experiment and narrow down all the variables until I am able to reproduce a better quality image. The important thing as far as I am concerned is this demonstrates yet another thing the 7000 series can do that no other scope is capable of.
Dennis
From: cheater00 .Sent: Tuesday, June 04, 2013 11:27 PM Hi Dennis, Regarding using any scope in raster mode; this one was a head scratcher when I first tried raster mode.. In TVs we're used to the point scanning from left to right in rows, and then it scans more slowly top to bottom.
Now what I want to see is someone using noise as the X and Y deflection, sampling something in this way, and then displaying it on the scope. Regeneration happens because you use the exact same noise signal. You don't need any sort of precise signal for carrying sampling information - it only needs to be accurate, not precise! (accuracy means you can repeat measurements with the same results, precision means your measurements are close to the intended value). So I want to see that, but it might need to wait until I've kludged together an SEM. Cheers,
On Wed, Jun 5, 2013 at 12:56 AM, Dennis Tillman <dennis@...> wrote:
[Attachment(s) from Dennis Tillman included below] There is a low power analog TV station still transmitting in Portland around 80MHz. Over the weekend a physics professor at Portland State University showed me his contribution to the list of impossible things only a 7000 scope can do. He displayed the image from the TV station right off the air onto the CRT. He did it on a 7834 (storage was off) using a 7B70 and a 7B92 in the outermost slots to generate a raster, and a 7L12 tuned to 80MHz to lock onto the TV station’s signal. A simple telescoping whip antenna was all he used. Attached is a photo I took of the CRT of the 7834. When I got home to Seattle I could not find any analog stations still transmitting in our area so I had to figure out a quick way to make my own TV station. The picture I took duplicates the professor’s work but with much poorer results since I was using a cheap wireless camera a substitute for the low power Portland TV station. Attached is an image I took of the QSL card from one of my ham radio friends – K7PJT. Contrast is poor due to the signal from the wireless camera but his call letters are clearly visible. The image was flipped and rotated to make it more readable so the on-screen readout appears sideways and backwards. Dennis Attachment(s) from Dennis Tillman 2 of 2 Photo(s) ,_._,___
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Re: TV on a 7000 Scope - impossible on any other lab scope [2 Attachments]
Hi Dennis, Regarding using any scope in raster mode; this one was a head scratcher when I first tried raster mode..very fun indeed! How is the 7L12 used here? I haven't got any ideas! In scopes, vertical deflection has a much higher bandwidth than horizontal. So you should have the point scanning top to bottom, and then the rows should slowly progress left to right. So it's actually the natural way for raster mode to be: turned sideways. D.
On Wed, Jun 5, 2013 at 12:56 AM, Dennis Tillman <dennis@...> wrote:
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Re: Explanation of the 7D20 "dip" straight from the 7D20 Project Manager
Hi Dennis,
On Wed, Jun 5, 2013 at 12:17 AM, Dennis Tillman <dennis@ridesoft.com> wrote: My understanding is that that isn't exactly true. An analog signal isThat is incorrect. The exact same problem exists in the continuous-domain Fourier transform, and basically in any other thing that assumes an unbounded continuous domain. This issue is called the "boundary problem". It has nothing to do with there being discrete points. It's about the fact that at some boundary (here, the start or the end) on one side you have enough information to reason about what's happening, and on the other side of that point you don't. Notice I said "information". According to the Shannon-Nyquist Sampling Theorem (which is true), the discrete-time signal contains exactly the same information as the continuous-time signal, up to Fs/2. Since we don't care about what's above Fs/2, that's *exactly* what we want. Discrete and continuous Fourier transforms yield exactly the same results, but to compare you'd have to do a lot of pencil-and-paper computation, so I'm not going to be able to show you something conclusive. The Sampling Theorem has very big weaknesses. For one thing, it assumes an infinitely-long oversampling filter during regeneration. Or more generally, when going from digital back to analog, it says it's *possible* to reconstruct the signal, but doesn't say *how*. Technology has shown it's absolutely impossible. In digital audio, you could encounter this waveform (assume 1-bit sampling depth): 1111111111111111111111111111101111111111111111111111111111111 What does it look like? Well, according to the Sampling Theorem, it's a sinewave which has had about 50 cycles during that span of time. To arrive at this conclusion, you have to analyze a long chunk of digital signal to even have the information needed to do it. That's because future samples in a digital signal may change your interpretation of the current sample you're interested in, and it's a major weakness of the Sampling Theorem. In fact, the closer the frequency you're trying to convey is to Fs/2, the more data you need to interpret it correctly and reconstruct it in analog - to have full sampling capability up to Fs/2 you have to make an infinitely-long oversampling filter, which is impossible. This non-determinism of analog waveforms produced according to the Sampling Theorem is just one weakness. Another (perhaps linked, I don't know..) is how badly it degrades. In analog, and this is especially applicable in audio, you have the following main forms of degradation: 1. noise. Noise is usually distributed in some uniform way and it just means the signal is a bit less clear. Noise is extremely easy to ignore, our minds are well trained for ignoring constant partials in signals. If you don't trust me, try this experiment that will use an optical signal. You're staring at a monitor right now. Is it dirty? Is the backlight equally bright everywhere? Our eyes normally don't track objects on the screen which helps hide this. Open up a new Notepad (it has a white background) and maximize it. Then open a second one, and make the window tiny, one inch across. Now move that new window while the first one is in the background creating a white field of light. While moving the smaller window, *track it with your eyes*. The object needs to be this big, the mouse cursor itself wouldn't work, it's too small. If you succeed at tracking the smaller window with your eyes while it's moving, you should see all the dirt you've been staring at for months without even knowing it's there. 2. non-linearity. This creates *harmonic* distortion which means that even the error is in some way related to the input signal. In music, it means the erroneous part of the signal is *musically related* to the original signal, therefore musically pleasing. Don't trust me distortion is musical? Ask Jimmy Hendrix. In digital, you have however the following main forms of degradation: 1. quantization noise. It depends on the *level* of the signal and on how many times it crosses a specific boundary. This is also called "bit crushing". The error signal is a high-frequency "zipper" tone that's difficult to ignore. If you want an example, find a wood-grain table and slide your finger nail across it. You'll hear a zip. This happens in exactly the same way as quantization: a specific signal (in this case, the position of your finger in space) repeatedly crosses sampling boundaries. If you use something that's more finely-grained, like a very fine plastic-top office desk, the zipper noise becomes less audible because there are more, smaller, finer "steps" in the grain. If you use glass there's nothing because it's so fine. Now here's the kicker: the best DACs in the world are unable to create steps so fine that we are unable to hear them. A lot of analog filtering has to happen for quantization noise to be removed 2. Aliasing. This one's absolutely terrible. The error signal's frequency content is in no way musically related to the desired signal. In fact, as your melody progresses, this one plays *against you*. It's like having a drunken monkey sit beside you on the piano, and it bashes keys exactly when you press keys. I currently don't know of anything that could alleviate those issues. There's no other way of digitally representing a signal sampled from the real world that I know of which doesn't have those problems. I have heard of mip-mapped sampling, but I haven't tried it yet and I don't know whether it helps, in theory there are some things it could be better at. Just my 2 euro-cents. D. In certain cases the discontinuity can be minimized, for example if the
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scanned: 5T3 Field Training
sipespresso <sipespresso@...>
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Re: Impossible Photo except on a 7000 scope
Don Black <donald_black@...>
I meant a scan of the manual, from other postings I guess it's
unobtainium platinum. Thanks for the explanations given.
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Don Black.
On 05-Jun-13 11:41 AM, Don Black wrote:
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Re: 7A26 Shuts down 7623A
Rob <rgwood@...>
I think the high points have all been hit. Look in the 7A26 manual and measure the + and – 15 and 50 V voltage supply pins to ground. You should see capacitance. i.e. starts at some ohms and builds higher or discharges and builds when reversing leads. If you only see resistance especially if it is low suspect shorted tants.
I agree with the post on not just replacing caps and hoping it fixes the problem. However once I have trouble shot and found the correct capacitor/s I usually do go ahead and recap the plug-in. The manual lists all the electrolytic capacitors so it is pretty straight forward to do.. Great care should be taken if replacing any on the ‘front end’ because some of the cards are made of a type of rubber (for lack of better wording). I do often skip replacing these as a result. Chemicals (even alcohol) can cause issues there as well. The manual has adequate warnings just need to heed them.
Another slight possibility is that the card slot in the mainframe is causing the problem. Make sure both sides have the white covers installed. These tend to keep everything aligned properly and if missing major headaches can arise.
Finally, and my biggest reason for posting because you already have been given great advice. If you are indeed going to just list them for parts. It might be wise to let it be known here 1st. I and/or others here would likely offer you reasonable amount and save you the listing fees, etc. more than likely allowing for a win-win situation. I think however you will quickly repair these two with the help you will receive here. It is a great community.
Thanks as always for the bandwidth. Rob
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Re: Impossible Photo except on a 7000 scope [2 Attachments]
Don Black <donald_black@...>
They're great photos. I've never heard of the 7J20 before, does
anyone know if a pdf scan is available n the Internet please. I'd
like to have a look and see what it can do.
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Don Black.
On 05-Jun-13 8:31 AM, Dennis Tillman wrote:
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Re: Impossible Photo except on a 7000 scope [2 Attachments]
teamlarryohio
Thanks! The ad with the DPO is great! I had a few of those cross my
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bench back then, but not with 7J's in them. I added the 1975 catalog which helped a bit. In any case, it's a pretty incredible piece of work. -ls- "Dennis Tillman" <dennis@ridesoft.com> wrote:
This may help. It is all I have in electronic form.
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