Oscilloscopes

[Cinderlane Productions]

Can I get away with using a 20 MHz oscilloscope to satisfactorily view
video waveforms?

I know that in order to trigger all the test signals properly, I should
use at least a 150 MHz unit -- preferably a conventional video waveform
monitor. However, I cannot afford one.

It is not my intention to measure rise times or verify parameters in a
professional capacity. Rather, I want to accomplish such simple things
as verifying that closed captioning is present in the correct vertical
interval line, determining that color burst and sync levels are "in the
ballpark," and checking for the presence of SCH frame-burst signals.

To reiterate, I will be using the scope too infrequently to justify a
major expenditure of funds, yet I want one with a bandwidth sufficient
enough to allow me to count the lines in the vertical interval and
identify what is in them.

 

[Dr. Anton T. Squeegee]

In article <26771-40F14B4D-134@storefull-3138.bay.webtv.net>,
Cinderlane@webtv.net says...

Can I get away with using a 20 MHz oscilloscope to satisfactorily view
video waveforms?

I know that in order to trigger all the test signals properly, I should
use at least a 150 MHz unit -- preferably a conventional video waveform
monitor. However, I cannot afford one.

<snip>

Video waveforms are complex beasties. That's why you have waveform
monitors. Even regular oscilloscopes need specially-configured
triggering to make sense out of them. That's why you see such features
as 'Video triggering' called out in the spec sheets on some models.

As for affording a waveform monitor, I've seen them for under $50
in some cases. Check Ebay. Check with whatever ham radio club is local
to you for close-in electronics-dedicated swap meets. Check with used
test equipment dealers. Check with pro-video editing places. Someone's
bound to have an older Tektronix unit that you can get for cheap.

In other words, scrounge like mad, and don't give up. It may take
a while, but I'll bet you'll find something.

It is not my intention to measure rise times or verify parameters in a
professional capacity. Rather, I want to accomplish such simple things
as verifying that closed captioning is present in the correct vertical
interval line, determining that color burst and sync levels are "in the
ballpark," and checking for the presence of SCH frame-burst signals.

Hate to break this to you, but I don't see any way that you can
determine all the above WITHOUT a true waveform monitor. Heck, at that
level, you may even need a vectorscope as well.

Happy hunting.

--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
(Known to some as Bruce Lane, ARS KC7GR,
kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
"If Salvador Dali had owned a computer, would it have been equipped
with surreal ports?"

 

[Bob Myers]

"Cinderlane Productions" <Cinderlane@webtv.net> wrote in message
news:26771-40F14B4D-134@storefull-3138.bay.webtv.net...

Can I get away with using a 20 MHz oscilloscope to satisfactorily view
video waveforms?

Depends on just what you mean by a "video waveform";
so the answer is, "possibly."

If you have access to "baseband video" (i.e., it's not on a VHF or
higher carrier) and we're talking about standard analog TV here
(and not high-res PC video), then - sure, why not? There's not a
thing in that signal that goes above about 5 MHz. But where you're
going to get in trouble is most likely in the triggering and delay
features - I doubt that a simple 20 MHz scope, unless it was originally
intended for such work, is going to have what it takes to easily, say,
isolate the vertical blanking interval and so forth.

Bob M.