mm wrote:

On Sun, 06 Dec 2009 09:17:54 -0800, Jeff Liebermann
wrote:

On Sun, 06 Dec 2009 12:03:52 -0500, mm
wrote:

On Sun, 6 Dec 2009 00:24:47 -0800, "Joe Rooney"
wrote:

Keep in mind a 3 way splitter has two 3.5db and one 7 db out.

Wrong. A splitter reduces the output by -3dB which is half the power.
The extra -0.5dB loss is from losses in the bifilar wound xformer. If
two of the ports each have half the input power, there's nothing in
the budget left for the 3rd port.

Googling for a typical 3 way splitter:
http://www.twacomm.com/catalog/model_CT413.htm?sid=1F79205DEA0D1B9FF1BF82ACDC4C33 D2

It says "3 way-loss 2 at 6.5 DB, 1 at 3.5 DB, 20 DB isolation DC
passive"

What does DC passive mean? Will it transmit DC power to an amplified
antenna, for example?


Yes. Some splitters will pass DC, usually only to one port.

The 20 dB isolation means that the return loss is more than 20 dB.
This is to prevent the local oscillator from one TV causing interference
to another TV. I was the engineer at a CATV system with over 10,000
active drops. There are hundreds of myths and half truths about the
hardware used for CATV systems.


I find 2 ports with -6.5dB loss and one port with -3.5dB, which makes
more sense. (Actually, it should be -7.0dB loss).


An ideal splitter would be 3 dB, 6 db, 9 db etc., but connector
losses, and to a smaller extent, core losses in the broadband
transformers add the fractional losses.


A 3 port looks like a tree. It starts with a two port splitter, where
one output is brought out for -3.5dB loss. The other port goes to yet
another splitter, with again divides the output in half, for -7dB from
each of the two ports.

Aha. That would certainly account for a difference! I'll check
later today. In fact, I'll take out the splitter and connect just
the one giving me trouble.

Except that you said you're using 2 and 4 way splitters, which are far
more common than a 3 way.

I did have a 4-way in there, but later on the slim possibility
something was wrong with the splitter, I switched and the next one I
found in my drawer was 3-way. Of course the problem pre-dates the
3-way, but I jumped to the conclusion that the 4 way might have had
something like this too.

I realize now I shouldn't have used a 4 way since i never had plans to
use more than 3 of them, but 25 years ago, I iddn't know they made
3-ways.

Thanks.


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