dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
1820
share rss forum feed


Edrick
I aspire to tell the story of a lifetime
Premium
join:2004-09-11
Woburn, MA

3 edits

CATV Signal Meter

So I'm getting more into some RF Distribution for venues we work for. (Local Access, Theaters, Live Venues) and every so often more and more I find that having a signal meter would be helpful. Being that it's all digital now pretty much I'd want something that does Analog and Digital.

So my question to you folks is what's a reasonable meter under 1k.

What are some important things that you might so pass along to someone starting new with using meters?

As far as using it to determine signal levels say for example I'm trying to check signal strength for a Comcast or Verizion system at the point of termination (cable box) as long as it's QAM would I be good to go?

I see a lot of "over seas" items when I google search which lead to eBay. So the question also would be are any of these good for the cause or is it really worth spending up to 1k vs. a $300 meter?

One scenario I've run into is ingress on the system, so a meter that can help with this would be great. I need to figure out where interference / noise is coming from.

Something like this maybe?
»www.sadelco.com/default.asp?page···ductid=1
--
Edrick Smith
Independent Film & Broadcast Producer
»edricksmith.com


DrDrew
That others may surf
Premium
join:2009-01-28
SoCal
kudos:16
AT the very least beyond signal strength measurements, you need the signal quality measurements of MER, BER (for digital) and C/N (for analog).

Ingress is helpful, as is leakage for finding cable damage, loose connectors, and other cable craft issues that allow outside signals in.
--
If you need help, I'm here for you. If you're wrong, expect to be called out on it. If it's important, have a back up or two. Don't complain in public if you don't want an answer...


Juke Box
His Word Never Fails
Premium
join:2001-01-29
Proverbs 3
Reviews:
·WOW Internet and..
·Knology
reply to Edrick
Fluke Network testers are superior. Such as the TS100 Pro Cable Fault Finder.
--
Pride is the only disease known to man that makes everyone sick except the one who has it.


DrDrew
That others may surf
Premium
join:2009-01-28
SoCal
kudos:16
said by Juke Box:

Fluke Network testers are superior.

Those are fine for twisted pair cabling but will not tell you channel strength or quality on cable systems, which is what the OP wants.
--
If you need help, I'm here for you. If you're wrong, expect to be called out on it. If it's important, have a back up or two. Don't complain in public if you don't want an answer...


Edrick
I aspire to tell the story of a lifetime
Premium
join:2004-09-11
Woburn, MA
reply to Edrick
One thing I've never understood is what the actual dB ratings mean. I've seen for example +30dB or -8dB

I understand a signal can be too hot / over modulated. But a good number to have might be around 7dB.

But what about negative?
--
Edrick Smith
Independent Film & Broadcast Producer
»edricksmith.com


Jabbu
Premium
join:2002-03-06
reply to Edrick
in a 75ohm system, 0db is a refernce to 1dbmV.

Good signal is usually around +12 to -8...

Most equipment will work well with any clean signal, you can have anything in that range, with noise and it will not work.

JDSU makes good meters, but $$$


p110011

join:2001-12-29
Oregon City, OR
Negative, meters read in dbvm's.
Not sure what a good digital level is, but for analog, 0-3dbvm at the back of the TV usually gets a good pic. Start going higher than 15 or 20dbmv, you might see some overdrive problems.
If you're into the low negatives with picture problems, or no picture for digital, than you need to start doing some adding and subtracting.
Say you have a couple of two way splitters, that's going to account for about -7db. If you have a drop of, say, 100ft, then on the higher chnls. you're going to loose another 6db, assuming this is RG6 cable.
So you add all your "normal" losses to what you've seen at the back of your TV set, that's what you should see at the start of the drop, if not, somewhere there is a problem.
Then you got whether it's high or low channels, higher frequencies ride outward from the center of the coax, (called skin effect) and low freqs. more on the center conductor. Most low channel problems are caused by some kind of damage or rust on the center conductor, or the conductor was trimmed too short and not making contact.
Get a cut in the shield, add water, dirt and time, you start having some higher frequency problems.


Jabbu
Premium
join:2002-03-06
reply to Edrick
Interesting, since a JDSU DSAM mentions nothing of dbvm, only dbmv.


p110011

join:2001-12-29
Oregon City, OR
Just a typo, it's millivolt

krommulent

join:2010-04-07
Reviews:
·Charter
reply to Edrick
»www.ebay.com/itm/Sadelco-5000-ca···74961440

i have used these and have coworkers that continue to. capable of leakage ingress, mer/ber, dig analog readings.


Edrick
I aspire to tell the story of a lifetime
Premium
join:2004-09-11
Woburn, MA
I think that model won't so ingress it's just the base model no?


Edrick
I aspire to tell the story of a lifetime
Premium
join:2004-09-11
Woburn, MA
reply to Edrick
I'm looking at the Sadelco DisplayMax Jr. 3000 the one i'm looking at has all the features I'd want.

So with a meter like that what are some ways you could use it to troubleshoot cable modems if at all? I understand there's far more to the matter than what you can tell me and I'm not actually looking to troubleshoot modems at this point but looking to learn more. The modems just use multiple frequencies and bond them together from what I understand. For example looking at my comcast modem i see 4 downstream channels.

Now further more i noticed they're all about -9db, so I'm still trying to grasp what exactly represents a 0dBmv signal, what represents no signal period. How do you know a signal is too low or too hot?
--
Edrick Smith
Independent Film & Broadcast Producer
»edricksmith.com


p110011

join:2001-12-29
Oregon City, OR
With RF you have to remember that the usage of db and dbmv are not the same. dbmv is an actual value, but db is a change or a difference in values. So saying -9db from what? It's probably -9dbmv, which is -9db from 0dbmv. Try reading this. »www.therealcableguy.com/tv-signal-levels.htm
It's really very simple.
Oh yeah, the 0dbmv you asked about is from the old days of cable and represents the minimal signal level needed for a good picture and it equals a millivolt.


Edrick
I aspire to tell the story of a lifetime
Premium
join:2004-09-11
Woburn, MA

1 edit
Interesting I did read that and understand it more.

I've found both the Saldeco 800 CLI and looked at a DM5-12300 from Saldeco new. What are your opinions, what are the main differences between the two?


Edrick
I aspire to tell the story of a lifetime
Premium
join:2004-09-11
Woburn, MA
reply to Edrick
Well my new gadget came in the DisplayMax 800. Now to sit down and learn how it works along with the basics of RF broadcast.

What started this whole project is I'm trying to troubleshoot a 500 feeder cable between a MDF and IDF. The outer aluminum shielding was snapped. I got the proper equipment to re-terminate that. However still no RF signal.

Any other ideas for testing this cable? It hasn't worked since they built the place in 2006. Perhaps there's a serious break somewhere in the cable. Continuity test maybe?
--
Edrick Smith
Independent Film & Broadcast Producer
»edricksmith.com


DrDrew
That others may surf
Premium
join:2009-01-28
SoCal
kudos:16

3 edits
TDR... time domain reflectometer. That will tell you the distance to the break. Had you said something about broken cable earlier, I would've suggested it earlier like Juke Box did...

They come in lots of varieties. Wide price range.
»www.amazon.com/Fluke-TS90-Cable-···t+Finder
»www.amazon.com/Megger-CFL535F-In···ctometer

Video on their use:

»www.youtube.com/watch?v=u0wvHJ9tjwE

--
If you need help, I'm here for you. If you're wrong, expect to be called out on it. If it's important, have a back up or two. Don't complain in public if you don't want an answer...


DrDrew
That others may surf
Premium
join:2009-01-28
SoCal
kudos:16
reply to Edrick
BTW are you getting signal at the break?


Edrick
I aspire to tell the story of a lifetime
Premium
join:2004-09-11
Woburn, MA
I'm not sure if there's an actual break. The solid sheild was busted at the connection on the cable so I fixed that figuring since the sheild / aluminum was completely busted and just showing the dielectric core. I reterminated the cable but still so signal. So I'm wondering if it's broken somewhere else. Oye but it runs three buildings over.


Jabbu
Premium
join:2002-03-06
reply to Edrick
breaks, suck outs, etc usually have degraded signal, no signal is usually a dead LE/amp in our system or a complete cut.


Edrick
I aspire to tell the story of a lifetime
Premium
join:2004-09-11
Woburn, MA
I've checked the signal being fed into the trunk no issue there. Just doesn't show up at the other end


DrDrew
That others may surf
Premium
join:2009-01-28
SoCal
kudos:16
said by Edrick:

I've checked the signal being fed into the trunk no issue there. Just doesn't show up at the other end

Do you know the path cable? Are there any splices or junctions of any type in it? Check for signal at those...
--
If you need help, I'm here for you. If you're wrong, expect to be called out on it. If it's important, have a back up or two. Don't complain in public if you don't want an answer...


Edrick
I aspire to tell the story of a lifetime
Premium
join:2004-09-11
Woburn, MA
It goes direct from the MDF to one of the IDFs although weather or not something happened to the cable along the way is anyone's guess. Without popping out ceiling tiles between multiple buildings following the path.


p110011

join:2001-12-29
Oregon City, OR
If your meter detects leakage, you might find a cut cable using that, if it is a cut cable.