Hello. I have an antenna in my attic and 2 digital converter boxes
and I'm ready for the digital switchover. There are a couple other
channels that I cannot get with my current antenna, and I'm
considering building an antenna as shown in this video and pointing it
in another direction:
My question is this....how do I add another antenna to my existing
system? Is it as simple as just running BOTH antennas into a
splitter? A splitter is generally used to split a signal into 2
signals, but can it work the other way (combining the signals from 2
antennas into 1 signal which will go to my TVs)?
Thanks a lot!
When I was a kid, our family home had 2 antennas on the same pole,
they were just wired parallel, the TV sorted it out. That was in the
days of flat 2 lead wire, but I don't see why it still wouldn't work.
I'd just use a cable splitter on the pole. For the bother this will
be, couldn't you just use a rotor.
Thanks for the reply. My attic is mounted inside my attic, hung from
the rafters using 2 hangers. It works like a charm, and I am afraid
to move it! It's just that there is another PBS station here locally
that I think might get with another antenna pointing in the right
Adding a rotor would certainly be more hassle than just adding another
antenna and combining the signals, wouldn't it?
The short question in all this is - can I run coax from 2 different
antennas into a splitter, then from the splitter to my TV, and get
signals from both antennas?
They're often called splitter-combiners, and there's a reason for
Inside that mystery box is nothing more than 3, 5, or 7 wires
connected together. The shell of the splitter-combiner serves to
connect the outer shielding of the coax cable, and the center pins are
connected through these wires.
No, that's not the case. If it were, you wouldn't
need splitters; all you'd need to do would be to
connect the wires together, which won't work due
to the impedance mismatch it creates.
It won't hurt anything to try it out, but ...
you'll end up with problems a lot worse than what
you started with. In order for power transfer to
be maximized, the impedances must match that of
the cable. If it's 75 ohm cable, then the
splitter will contain, minimum, a set of 75 ohm
The resistors allow impedance matching to the
cable, maximize power transfer, and keep
everything looking like the same impedance to the
antenna, TV, and whatever else may be in the
lineup. That's also the reason you often need to
add at least a 3 dB amplifier to a line if your
signal quality is minimal and you can't afford to
RS carries some decent amplifier/splitters for
the purpose you're talking about. They properly
mix the signals from the antennas and then add a
power boost to amplify the signal (but not the
noise) back up to at least the level you had
before you added anything to it.
I have a similar situation to yours; we're in a
fringe area where the signals for DTV get pretty
iffy with rain & snow or even just high humidity
sometimes. Instead of another antenna though, I
got myself an 80 Db variable amplifier to put on
the antenna. It's a multi-directional antenna,
and boy, did THAT make a difference! If the
signal can get here now, I can see it<g>! I even
picked up a couple more I didn't know existed. It
hasn't snowed yet since I installed it, but it
looks like tomorrow I'll get to find out just how
successful it really was or if I wasted my money.
Stupid amp cost around $60! Oh well.
Most splitters, excepting the cheapie junker
ripoffss will at least have resistors between the
internal points such that no matter which port you
measure, you will see the same
resistance/impedance. That way the maximum power
transfer can be maintained. If it were just wire,
the impedance of the wires would be seriously
mismatched, and there would be almost no power
transfer to the TV set, meaning very little
signal. It's the impedance matching to the cables
that makes splitters work. Each splitter results
in about 3 dB (half power, or half the watts) out
compared to what goes in; that's the max power
On Tue, 20 Jan 2009 08:10:07 -0800 (PST), Mike wrote:
Yes, you can do this. You might get lucky.
You WILL introduce mutipath problems. The question is, whether the
problems will be bad enough to be noticeable. If you're in or near an
urban area (lots of man-made structures), its likely you'd notice more
problems than if you were out in farm country.
Even though the second antenna is not pointed at the sations you get
from the first antenna, it will receive some signal on those channels.
The signal it gets might include a reflection off of a building
somewhere. These copies of the signal arriving over multiple paths (thus
the term multipath) don't add up simply. Its difficult to explain in a
short message, but the bottom line is that you might improve reception
for some stations, and make it worse for others. If you are looking at
analog TV, you'd see ghosting as a symptom of multipath. In a digital
transmission, mutipath can cause data loss. The digital tuner probably
has circuitry that compensates for some degree of multipath, but if its
bad enough, the circuitry won't be able to compensate fully and you
won't see a picture on the affected channels.
It is impossible to accurately predict what will happen. If its easy and
cheap enough for you to try it, go ahead. Worst case, you'll decide to
run a second line down to the TV and use a switch instead.
Two problems with that, and a possible fix:
Problem is, you have two outputs fighting each
other; one is going to sink/source power to the
other. Could result in anything from a crummy
signal (weak) to no signal.
A splitter will cut the signal strength regardless
of how it's used, and especially as you mention.
Look for an amplifier/mixer with two inputs and a
single output if that's all the outputs you need.
Then you can get a few DB boost in the signals,
mix them properly, and get them to your TV. I
haven't noticed anything like that at RS but have
at specialty shops.
Yes, you can reverse the splitter to make it combine the two signals
and keep the proper impedance. The only problem is.........the two
antennas may be located far enough apart that the signal induced
into antenna A may be out of phase with the signal induced into
antenna B. When this happens with an analog signal you may
get ghosting or just a reduced signal level that would not justify
using two antennas. With a DTV you may get a inferior signal level.
To reduce the possibility of out of phase antennas you should try to
mount them side by side so that the distance to the transmitting tower
is the same for both. On the upper frequencies a half wave or 100%)
phase shift is only 8 inches. On the lower frequencies it is around
2.5 feet. Keeping the antennas perpendicular and side by side is your
best bet. Signal deflection from mounting the antennas inside could
also cause a out of phase problem. Good luck.
On Jan 20, 3:16 pm, email@example.com wrote:
But the OPs problem is (and this is probably common) he wants to pull
in signals from different transmitters at different compass points.
He wants one antenna 'pointed' at one transmitter, and another antenna
'pointed' at another transmitter. If you can't combine two separate
antennas in this way without their interfering with one another, maybe
a rotor really is the only way to do it. -- H
I've had good luck with attic antennas.
But the tv wants to "see" one particular impedance, 50 or 75 ohms (I
no longer remember. It may even have changed.)
Amateur radio types use antenna matching networks (tuners) to make
sure the equipment matches the antenna impedance. You might need one
Easiest of course is an A/B switch. That's what I'd do. Though it
won't work with your remote.
They're at different frequencies. I don't think they will interfere.
But resistances connected in parallel are much less than either
alone. You may have too much impedance mismatch to get the signal
into the tv without a matching transformer.
A signal amplifier *might* do that for you, I'm not sure how they are
Honestly...putting dual antennas up will only give you a 3db gain if
everything goes well. A 3db gain is not much when you are talking
about a DTV signal.
If he is looking for a antenna structure that needs to be
multidirectional that is located in the attic then he is basically
entering into a non predictable situation. It would be a trial
and error situation.
As you have suggested one antenna, one amplifier mounted at
the antenna, and a rotor would be his best bet in the attic.
Better yet would be to get the antenna outside. I suspect that
one omni directional antenna without a rotor or amplifier would
do just as good or better.
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