It's been a good while since I visited; hope this finds every one doing well, or at least ordinary.
This question might be more suited for the Sat Forum, but I thought I might have a better chance of the right person seeing it here. So here goes...
Occasionally, the outfit I work for will install a Satellite Master Antennae Television system. One bit of knowledge I would like to get is this: How can I be sure that the video modulation level on the individual modulators is set to a common standard? Now, I realize that I could make phone calls to Scientific Atlanta, or B/T, etc., etc., but I don't really have the time during the day to do this. Any experience out there?
Thanks!
Jeff

You could test their outputs with a field strength meter

So far so good. Let's go a little further, though. What should my input source be? Does the meter itself provide a separate unit to generate a signal, like the Acterna kits that we use? Is there one you prefer?
What would I actually be measuring?
Thanks!
Jeff

I'm not sure if the input signal matters when measuring the RF output. Even with no signal appllied, the modulator's output is still active. Maybe someone else could further elaborate on that.

There's a number of RF field strength meters on the market. Here's a couple of places to get started:

[Link: sadelco.com]

[Link: sencore.com]

In the rare cases when I need one, I use an older, analog RL Drake model.

What you're measuring is the frequency dependent output level of the modulator in DB's. That's what you were wanting right?

Ixnay. But I see where I went wrong. In your first response, you referred to a field strength meter. I keep telling myself to stop doing this late at night, but I never listen to me either...
We have an Acterna two-piece kit consisting of a signal generator and a field strength meter. Pretty amazing piece of gear; lay out of 723 foot long piece of RG-6, walk along and pick a spot at random and dent it with your fingernail. I'll tell you where the dent is. Want to know if the cable system you pre-wired is leaking now that you've trimmed it out? If you live near South Hampton Roads in VA, drop me a line. Anyway...
In my grape Kool-Aid induced fog, I thought you meant a spectrum analyzer. We haven't bought one yet. What I'm trying to measure is the level of video modulation, as opposed to RF Level Output. This kind of adjustment isn't found on homeowner equipment.
This control affects the contrast level (among other things) in the generated picture. If they're not set to a common standard, you get varying levels of contrast across the different channels you're sending to the customers. Sure, you can go along and tweak it 'till they all look okay, but the term "bush-league" comes to mind.
Sorry I helped you onto the wrong train, AHEM. Still could use some help, though.
Thanks!
Jeff

jeff I think you are looking for a device like flukes microtester, it uses time domain reflectivity (TDR) to determine the length of wire, if their is an open, or a short, and where. It will test coax, 2 conductor or network cable. It is about $400 and you can pick one up at ADI. What it won't do and this may be what you are looking for is to determine the impedance in the line to see if their is a shift away from 75 Ohms (I.E. a bend in the cable, enough to affect perfomance) for that you will need to spend a bit more money, but fluke makes everything you would ever need to determine problems with wiring, as well as perfomance of the wiring, even before sheetrock is up. I live in Richmond VA so if you want to talk about it, send me an email w/ your ph # and I can give you a call.

I think Jeff's looking for a device along the lines of what a cable company would use to calibrate the front end of their modulation equipment.

I want to say you'll be needing a waveform monitor and vectorscope but that would be looking at the baseband. If I'm reading you right, want to measure the signal post-mod. Hmmmm.

Just ring up Jeff Goldblum and have him bring his ancient PowerBook. He'll square you away right quick.

I was out of town alot last week, and some generous soul shared his viral infection with me. Being the selfish sort when it comes to that kind of thing, I have spent virtually all day at home so that nobody gets any of mine. It's miserable, but the thing about Jeff Goldblum lightened the evening. Thanks, Wags! And you're correct; I would be looking at the output of the mod. And AHEM is on the right track, too. mr2channel, we have on the of those gizmos that employs TDR. Ours is called a Shortstop. Indespensible in this kind of work. Tell you what, though; I will zip you an email. Most of my time last week was in Chester. Over the course of the next several months, including next week, I'll be there on and off. Maybe we can trade a couple of brews and a war story or two. Same for Larry.
As far as the original problem, I'm going to put in a call to Pace in FL. They sell us most of the wizzo stuff we spend thousands on. I'll drop the ball in their laps.
Thanks again, all!
Jeff

You probably heard that term loosely used by a ham radio operator.

Field strength meters have a small antenna and are used to measure the intensity of the FIELD broadcast by a transmitting antenna. You are talking about signal level meters.

Edit: Ah. I see you addressed this.


How could you possibly set them to a common standard if this kind of adjusment isn't found on homeowner equipment? I understand that you might want to see what the modulation levels are if you need to tell a person why channel A or B, or the modulator, just plain sucks, but is there something that you could do about it?

Actually, something comes to mind. Let's imagine for a moment that the home modulator does not have AGC on its input. That costs money, so it probably doesn't. Then, since picture is Amplitude Modulation, changing the video signal level will change the modulation level, and this can be done outside the modulator.

When you or your clients look at channels or the results of this experiment, note that since all televisions DO have agc, you will not actually see what your adjustments have done. For that you need a Production Monitor.

This message was edited by Ernie Bornn-Gilman on 01/30/05 14:23 ET.

EB-G,
Thanks for the response. Yes, I used the wrong term there for our Acterna. That is a leftover from when I worked for a TV shop that used to help set up off-air antennae systems so they could get the local PBS broadcasts.
You make a good point about the "common standard". My thought there is that there is indeed some standard level of modulation, the level being determined by knowing what TV's need in order to accurately reflect the picture's original dynamic range, and all manufacturers of homeowner mods sticking to it. However, what I could get by with is a way to measure the level, set one mod to what looks like an ideal picture on a decent monitor, then set all the other mods to the same amount.
Thanks again!
Jeff
Also, as an aside, we have had a number of mods that needed the modulation levels reduced in order to eliminate serious blooming and picture tearing in white areas of the picture.