On 1/7/2014 10:55 PM, Sal wrote:
"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.

"Sal"
(KD6VKW)



In addition to the splitter losses, you have coax and connector loss.
Coax loss probably isn't too bad, but unless you use a high quality
crimping tool, connector loss can easily approach 0.25 to 0.5 db. Even
with a high quality crimping tool, you can get around 0.1 db per connector.

There is also the possibility of a slight phase difference of the
signals coming out of the combiner, which would also affect the output
(splitters/combiners aren't perfect, either). But I wouldn't think this
would show up at such low frequencies unless you have lab-grade test
equipment (microwave frequencies and above are a different story).

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Jerry, AI0K

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