In the case of the VGA signal I looked at to play with the video sync
on my 2440, I used sync on green instead of the separated horizontal
and vertical sync signals.
On Mon, 9 Jul 2012 22:39:06 -0700 (PDT), Denis <xyzzx_adv@...>
wrote:
? Having restarted this thread by mistake (I had intended my email to John directly but goofed) I will try to shed some light.? John' original comment on this thread (4 Mar 2011) did a good job of describing the NTSC signal and challenges of syncing a scope to the video stream with embedded V and H sync signals.
?
? Granted that VGA signals are similar in that they provide analog video signals, but they also provide H and V sync on the connector pins (not buried in the video stream).? So it is possible to setup the scope to trigger the 'A' Sweep with V sync and use the delayed sweep feature to effectively move down the computer screen and trigger the 'B' Sweep with H Sync and see an individual line of video.? Now, 'back in the old days' it was possible to connect a video monitor to the scope (524A) and see which line you were observing on the scope (it was brighter).? A trick I learned was to work my way down the monoscope resolution fan and adjust the focus by watching the HF amplitude increase as it got sharper (this was back in the days before computer generated images) when TV was Black and White.?
?
? While the Video option probably would do a good job of syncing the scope, the availability of the sync signals preclude the necessitity of the sync separator that the option provides.? Plus, since the VGA signal is progressive not interlaced all video fields are the same and there is not the need to identify them (NTSC on the other hand has four unique?fields, odd and even lines, 'A' frame and 'B' frame, which differ in burst phase polarity).? All of which is getting pretty deep into an antique video format (at least in some circles).? But, which leads me to answer Bob's question that I can't think of any other use for the video sync option.
Denis
________________________________
From: David <davidwhess@...>
To: TekScopes@...
Sent: Monday, July 9, 2012 12:13 PM
Subject: Re: [TekScopes] Re: Video triggering of 'scopes in general
?
I have a broken 7B53A with the video option that I may get around to
repairing some day. When I asked about it here, I was told that the
mixed sweep feature of the 7B53A is particularly useful for examining
video.
My 2440 has the rare video triggering option. The only time I have
used it was when looking at a VGA output and it worked great. In the
case of the 2440, it includes features like field and line selection.
Oddly enough, worked correctly with 1050 and 1200 line video.
On Mon, 09 Jul 2012 17:52:43 -0000, "Robert"
<mailto:go_boating_fast%40yahoo.com> wrote:
Some 7B53As have video sync. I have two. Don't really use that feature but they work fine anyway. Might check those manuals as well.
Also, Is that feature good for anything else?
Bob
--- In mailto:TekScopes%40yahoogroups.com, Denis <xyzzx_adv@...> wrote:
John,
?? I would like to request a copy of the 453 Mod 127C Schematic.?? I still have some NTSC gear around and want to see how Tek implemented sync separation, for possible inclusion into a 453A.
??Thanks,
Denis
________________________________
From: John S <John@...>
To: mailto:TekScopes%40yahoogroups.com
Sent: Friday, March 4, 2011 9:21 AM
Subject: [TekScopes] Video triggering of 'scopes in general
??
- All the old TV standards adopted around the world have an odd numbers of lines in a "complete" picture, which is defined as a TV Frame. (25Hz Europe, c.30Hz USA)
- To conserve RF bandwidth, the signal is transmitted in sequential Fields, each of which contains half the lines (odd lines Field 1, even lines Filed 2 etc), as required to assemble the full TV Frame.
- This is known as interlace scanning, and gives rise to display artefacts such as line-twitter on strong horizontal black-white transitions.
- As the odd number of lines is clearly not divisible by 2, odd fields terminate (theoretically) half way through a line, and even fields commence similarly.
- The problem confronted by TV engineers is to get the 'scope to trigger stably (ideally) at the FRAME rate, which is half the field rate. This allows a 'scope with a good dual-time-base delayed sweep to select a particular line. (The line can be a bit dim, as the 'scope is only writing for c. 60uS in every c. 40mS).
- I have a 453 with TV triggering ( MOD127C ): Tek used to supply special graticules (which I also have) based around standardised TV test & measurement waveforms.
- broadcasters use a few of the "blank" lines in the field blanking area* to transmit the test waveforms so an entire transmission chain can be quality monitored
I can supply a copy of the MOD127C 453 handbook description to anyone who's interested.
John
* the "field blanking" lines contain synchronising pulses which are "broader" than on normal video lines, and the shift in DC level is used by the sync separators in the TV to lock the frame oscillator to field rate. They were kept free of video in order to allow the CRT scan time to return to the top of the screen without losing active picture content.
--- In mailto:TekScopes%40yahoogroups.com, Gala Dragos <gala_dragos@> wrote:
Hi!
I've worked with a TD2002B recently. It had a trigger mode named "Video". It was used to display PAL/SECAM/NTSC video signals and lines. How do I do that with Tektronix 475 or 465 ?
Thanks.
David Hess