In message , Sal
writes

"Jeff Liebermann" wrote in message
.. .
On Mon, 6 Jan 2014 06:28:11 +0000 (UTC), gregz
wrote:

wrote:
"only 3 db", but that's twice the signal. I have mine stacked 12 feet,
but I believe Winegard says either 8 or 10 feet. Mine work swell. +:^] I
got mine just after they were discontinued in 2005/6. Had to email a
number of suppliers until I found the second one. I bet there are some
still in storage somewhere, email different places that sell Winegard,
you may still find one.

John K9RZZ

Twice the signal means twice the voltage, for me.
Greg

Nope. Power is by the square of the voltage:
P = V^2 / R
If you double the voltage, you get 4 times the power.
A 1.414 times increase in voltage will produce twice the power.

I tried to convert the antenna model of the HD-6066P antenna from the
AO .ant format to .nec using 4NEC2 and failed. The plan was to model
the stacked arrangement and see what happens:
http://www.ham-radio.com/k6sti/hd6065p.htm
The .ant file imported without error, the wire tables and images look
correct, but the pattern is more like a point source than a gain
antenna. I'll look at it later to see where I screwed up, but it
would be nice if someone would look at the problem.

I just set up an experiment. I connected my roof antenna to my signal
level meter and read the signal strength of my Channel 10. It was 10 dBmV,
the unit typically used for TV signal strength work.

Next, I connected the same roof antenna to the inport port of one of a pair
of passive splitters connected back-to-back with equal short lengths of the
same 75-ohm cable.

Finally, I connected the output port of this network to the signal level
meter and observed a signal that was approximately 1.25 dBmV less. (A
quarter of a dBmV is about as close as I can reliably read; individual whole
number marks are only a few mm apart.)

Thus, I conclude that the 1 dB nominal loss for a passive splitter -- either
combining or splitting -- is confirmed. Combining two identical suignals
does get you something more than one, alone.

RELATED: When I used identical twin UHF antennas side-by-side, separated by
a free-space half-wave distance to cancel interference from one side, it
worked nicely and showed about the same loss figures as above. That is, my
reading for two antennas combined was about 2 dBmV higher than for either of
the twin antennas alone, thus reflecting the 1dB loss in the combiner.

Combining antennas can be an uncertain business because the phase
relationships change with wavelength; the arrangement that strengthens one
channel may weaken another channel if the respective signals come from
different directions and/or the cable lengths are not matched. It's a
matter of reinforcement or cancellation, depending on phase relationships.

You missed out step #2, which was to measure the output level of the
splitter alone.

Using your figures, this would have shown a signal loss of 3.625dB (3dB
power split loss and 0.625dB of circuit loss).

When you then added the combiner, you would have 3dB power split loss
and 0.625dB of circuit loss, followed by 3db power combine gain and
0.625dB of circuit loss - so as you measured, a total loss of only
1.25dB.

Despite working in the cable TV industry for 43 years, for some reason
this is an experiment I don't recall ever performing!
--
Ian

"Ian Jackson" wrote in message

You missed out step #2, which was to measure the output level of the
splitter alone.

Using your figures, this would have shown a signal loss of 3.625dB (3dB
power split loss and 0.625dB of circuit loss).

When you then added the combiner, you would have 3dB power split loss and
0.625dB of circuit loss, followed by 3db power combine gain and 0.625dB of
circuit loss - so as you measured, a total loss of only 1.25dB.

Despite working in the cable TV industry for 43 years, for some reason
this is an experiment I don't recall ever performing!

Thanks Ian,

Earlier in this thread, I saw what I thought to be an error in some postings
.... about losses in excess of 3dB in the combiner and a conclusion that
stacking results in less signal, which shouldn't be the case. My little
experiment was meant to demonstrate a signal increase from combining
in-phase signals in a passive device. Put another way, I wanted to show
that a 3dB loss is not inherently present in both directions.

You are correct that I did not make the measurement of the output level of
the splitter alone, since it has been made and documented on many occasions.
A real lab experiment would have measured that and the cable losses, too.
(My 35 year-old Jerrold 747 was within easy reach and "close enough.")

It was my intent to show, when two equal signals (presumptive on my part
that the two outputs of a splitter are equal) are combined, that the result
is the addition of the two, minus ohmic and coupling losses, which I think I
did show.

"Sal"