RF question...

Not sure if this is the right group but I have a question about RF strength.

When using a DOCSIS modem the forward and reverse signal need to be within a
certain strength. reverse should range from 35dB to 55dB.

when adding a splitter to the cable line it usually lower the dB. However,
sometimes there will be a modem that is getting too strong a reverse signal.
58dB and when we remove the splitter it goes to 50dB or something similar.
what is happening here? how can the signal strength decrease when REMOVING
the splitter????

 

If the barrel used to replace the slitter is bad, that would do it.

You need to test this with one output port of the splitter
terminated. That way you're only measuring the reverse signal on a
single line. Bad sheilding or connectors on any line can introduce
interference into the system - ingress.

 

Thanks, I never thought about that....

 

If it tests ok that way, you can reconnect the 2nd line and
terminate the end to see if that line and its connectors are right.
then when you connect up the other modem and send 2 simultaneous
returns, you can expect to see both returns combined, less the
insertion loss. The isolation between splitter output ports is also
important and splitters *do* go bad.

 

Hey, that brings up a 2nd question ... I've known that splitters can go
bad for quite a while, but what actually goes "bad" in them? The few
splitters I've opened only have a piece of wire coming from the input to
each output. These were low frequency splitters so maybe that is why they
were so simple but what can break in any of these splitters?

 

coils

GND IN
| |
| ___ |
+--UUU---+
___ ___
+--UUU--+--UUU---+
| | |
| === |
| GND |
| |
|----/\/\/\/-----|
| 150 |
OUT OUT