hey guys, quick question

do you know if catv couplers like the one i have below cause db losses? or does that only happen with splitters?
thanks

http://www.cablesunlimited.com/images/Medium/AUD-4000.jpg

Since they're hardwired, there's no real signal loss, but as with other passive electronic parts, there's a slight (one or two tenths of a dB?) loss of quantity and quality due to the additional solder and mechanical connections.

It just adds to the line loss. The longer the cable run the more loss you have. But it's generally minimal. A 100' run of RG-6 will have a loss of 2-6dB depending on where the channel is on typical 750MHz Digital Cable feed. So the couplers are of little consequence as you may loss fractions of a dB on one of them.

CCourtney

thanks

there's no real signal loss,


there's a slight (one or two tenths of a dB?) loss of quantity and quality

Which is it?

RG-59 in line barrels have about 2 db of loss. They also have a VSWR issue that can be worse than the db loss depending on the frequency.

RG-59 in line barrels have about 2 db of loss. They also have a VSWR issue that can be worse than the db loss depending on the frequency.

Agreed (even if the barrel is used on RG59, RG6 or RG11).

Also, you should make sure you have the blue plastic in the barrel indicating that it is rated to at least 2Ghz.

Which is it?

2db and up to 3db on some runs.

A CATV quality F-81 connector will have less than 0.5dB of loss through it. Check PPC's specs here: http://www.ppc-online.com/products/drop/tools_access/F81s.php

I can't speak for Pacific Rim knockoffs, but other American manufacturers like LRC and Gilbert will be comparable.

Mallago

2db and up to 3db on some runs

I see, you've got the magic cable, that only loses 2 to 3 dB, regardless of length, and termination. ;)

you are going to loose under .5 db with f 81's.

.2 to .3 on the better ones

I use them at work in a lab for cable TV testing and typically I only see a few tenths of a db.
I have only had vswr issues with the 90deg type (never use them).

I see, you've got the magic cable, that only loses 2 to 3 dB, regardless of length, and termination. ;)

Speaking of the connector - not the cable loss.

Depends on the type cable and quality of the matting of the connectors.

Thus 2db loss with the barrel and up to db of loss depending on the cable/connector fitting.

Seems everyone else posting is color blind and can't see that the difference in white and blue (or know why its significant in terms of rating and quality) - and CATV does not use the F81s in the above links - they use F81s rated to 1Ghz like the OP pictured.

I have personally seen the VSWR issues when mating a short RG-59 jumper and RG-6 at L-Band with F connectors rated for the frequency. Not a pretty sight. It made a usable signal almost totally disappear.

Speaking of the connector - not the cable loss.


Seems everyone else posting is color blind and can't see that the difference in white and blue (or know why its significant in terms of rating and quality) - and CATV does not use the F81s in the above links - they use F81s rated to 1Ghz like the OP pictured.


FanAtic, that the CATV industry doesn't use the F81s that I linked to is kind of a broad statement, don't you think? The losses shown are realistic for name brand F81s. More important than insertion loss is return loss. This has more of an impact as foxeng pointed out. F connector measurement procedures are called out by SCTE standards like this one: http://www.scte.org/documents/pdf/ANSISCTE051999IPSTP408.pdf

As I mentioned, Pacific Rim products usually don't come with specifications, mostly because they are knockoffs and do not have the performance testing done.

I certainly won't say that CATV companies don't use cheap connectors, some do and some don't.

The bottom line with all of this is that, yes, there is some amount of loss, however, it shouldn't make much difference in most applications. If you are worrying about one dB, it won't play anyway.

Mallego

I've seen big problems with RG-59 cable and these things; it seems that at least with some of them, the connector doesn't grip the thin RG-59 conductor securely.

I've seen big problems with RG-59 cable and these things; it seems that at least with some of them, the connector doesn't grip the thin RG-59 conductor securely.

If a crimp connector tool will not crimp a connector on securely, you can effectively reduce its jaws "die size" by putting a few sheets of paper in between the jaws. The cheap RG-11 crimp connector variously marketed as Tru-Spec and under other unimpressive names, almost never crimps an RG-11 connector securely, either, so I always used to bring a manila folder with me to use as jaw shim stock when I went on service calls in which I might need to install such connectors.

FWIW, I spoke with tech people @ cable today and they informed me that with the expansion of system frequency as well as internet and VOIP demands they (as well as most MSO systems) went to a higher quality barrel and the loss is now far less than 0.5db with them.

The only downside is that with an electrical hit, the connectors at that point is weakened and has some issues.

Of course from perspective, if you take an electrical surge or hit, that is probably the least the of your issues.

So I stand corrected as clearly the industry has made the shift to a better quality barrel, primarily due to the areas listed above.

I clearly would look for blue dielectric indicating the higher rating than the white dielectric. (I will also tell you that I only recently purchased my first bag of higher quality/blue dielectric barrels connectors compared to just picking junk of the shelf @ Rat Shack or Best Buy and I guess my weekend project will be replacing any of those older barrels that I have left over in any areas around the house).

You guys actually measuerd 1 db PER fitting loss?? I have always figured 1/2 db per fitting and I thought that was generous.

Depends on the quailty of the connector and yes I have measured more than 1 db loss at TV UHF frequencies before.

That's why the F-Connector is not considered to be a real connector. A "real" connector has a center pin and associated construction to control the impedance. The F-connector was developed because it was cheap. Period.

IOW, use the center conductor of the coax in place of the contact pin. Used by the CATV industry when the maximum frequency was around 300 MHz. Now, they're pushing 1 GHz, which was an unthinkable objective at that time.

Connector loss is roughly proportional to sqrt(frequency) and should be around .05 dB or so. Except for the F-connector. Here's a quick backgrounder from Amphenol: http://www.amphenolrf.com/rf_made_simple/techquestions.asp