"Ian Jackson" wrote in message

Strange as it may seem, if you use (for example) a TV 2-way '3dB' splitter
to combine two identical in-phase signals, you DON'T lose 3dB. Apart from
the unavoidable slight inherent losses of the two transformers the circuit
uses (a total of around 0.5dB at low VHF, increasing to 1dB at high UHF),
the splitter is lossless. Ignoring the transformer loss, the 3dB loss
occurs simply because the power at each output port is half of that at the
input. You haven't actually lost anything.

If the splitter is now turned around to become a combiner, it doesn't
suddenly become more lossy. If you again ignore the transformer losses,
the two identical in-phase signals you feed into the 'output' ports are
added, and the result is a signal 3dB higher.


Jeff found a url with the specs for the combiner.
http://www.solidsignal.com/pview.asp?p=cc7870&d=winegard-cc-7870-2-way-tv-antenna-joiner-coupler-(cc7870)

It says 3.5 db of loss. I assume they use the simple resistor network
instead of transformers. If so, then the net results not counting feedline
loss would be a minus .5 db.

That combiner does not seem to be made to add signals from idinitical
antennas for more gain, but just to let you use one feedling for several
differant antennas such as putting a FM antenna up and a TV antenna up, or a
seperate UHF and VHF antenna up and using one feedline to the receiver.

I have one for designed for my ham transceivers,and have measured less
than .5 db of loss, but that is for differant frequency ranges and not to
combind two antennas on the same band.


Even if he does get the maximum of 3 db of gain, will that acutally get him
anywhere ? Will that be enough gain for the FM broadcast band to be
noticiable ?



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