Two Antennas for HDTV OTA?

Hi! Does anyone know if I can run two roof top antennas concurrently? I
live between two metropolitan areas that are about 60 degrees apart. Can I
point one antenna to the north, and then use a splitter to add another
antenna pointing south west? Then I'd run the one cable into my HD
receiver. I've heard that analog signals may ghost because the two antennas
are receiving the signal at different angles. But would a digital broadcast
do the same thing? Thanks!
--
Richard

Richard Minami:

Hi! Does anyone know if I can run two roof top antennas
concurrently?

Can't you just use an omni-directional antenna or a rotor?

But would a digital broadcast do the same thing?

Digital broadcasts do not ghost. You either get them or you don't because
the receiver cuts out when the signal strength is below a certain
threshold (somewhere around 80%).
--
Mac Cool

Mac Cool wrote:
Richard Minami:

Hi! Does anyone know if I can run two roof top antennas
concurrently?

Can't you just use an omni-directional antenna or a rotor?

But would a digital broadcast do the same thing?

Digital broadcasts do not ghost. You either get them or you don't
because
the receiver cuts out when the signal strength is below a certain
threshold (somewhere around 80%).
--
Mac Cool

You're most certainly mistaken on this one. Digital most certainly is
sensitive to multipath (ghosts) though it does not show up as a second
image displaced from the main signal. The delay equalizer in the
receiver can process much of the multipath out but not always. When it
gets beyond the range of the processing, it will fail regardless of
signal strength. BTW I've had good reception with very low strength
(50%) - measured at 12dB above the noise floor of a Tektronix 2712
spectrum analyzer. (ok, it's cheating).

The original question is about multiple antennas. I'm sure it _can_ be
done but may require some channel selecting filters and/or directional
couplers to avoid re-transmitting the signal from the north back out
the south.

GG

G-squared:

You're most certainly mistaken on this one. Digital most certainly is
sensitive to multipath (ghosts) though it does not show up as a second
image displaced from the main signal.

Wait, you are agreeing with me and claiming I'm mistaken at the same time?

I don't think the guy cares what is going inside the receiver, he wants to
know if the picture will ghost even though he said 'signal' instead of
picture.
--
Mac Cool

"Richard Minami" wrote in message
...
Hi! Does anyone know if I can run two roof top antennas concurrently? I
live between two metropolitan areas that are about 60 degrees apart. Can
I point one antenna to the north, and then use a splitter to add another
antenna pointing south west? Then I'd run the one cable into my HD
receiver. I've heard that analog signals may ghost because the two
antennas are receiving the signal at different angles. But would a
digital broadcast do the same thing? Thanks!
--
Richard

You will have ghosting problems called multipath. You probably need to have
filters or traps installed. I solved this problem by having two separate
paths each with it's own antenna and preamp then inside I trap the signal
from the antenna not pointing at the channel you want to receive. Depending
on your channels you can band trap if for instance one direction has UHF
channels and the other only VHF channels. Two 8db traps in one package costs
$28.00. You will need one of those for each channel you receive. As a
general rule of thumb you need to have 10 db of clean signal riding on top
of the noise, multipath or cochannel interference.

Best reception is with VERY directional antennas. Not only do you get
better signal levels (more gain) but you have less multipath from multiple
antennas.

Worst gain but free from most multi path is a omni directional antenna.
These are selling at Radio Shack for $70. Consider the cost of traps and
filters can easily run to $300 and it might pay for simple omni on a tall
tower (trade cost of traps for extra height).

Richard Minami wrote:

Hi! Does anyone know if I can run two roof top antennas concurrently? I
live between two metropolitan areas that are about 60 degrees apart. Can I
point one antenna to the north, and then use a splitter to add another
antenna pointing south west? Then I'd run the one cable into my HD
receiver. I've heard that analog signals may ghost because the two antennas
are receiving the signal at different angles. But would a digital broadcast
do the same thing? Thanks!

Combining 2 antennas is usually a tricky project getting 2 directional
antennas aligned just right or a complicated & expensive project
involving jointenna filters.

Depending on the distance to the two sets of broadcast towers, you may
be able to use a single antenna which is a heck of a lot easier and
cheaper. Or just live with the hassle of a rotator. Or 2 antenna lines
running down to the receiver with a remote controlled A/B switch (real
pain with digital receivers and channel scans).

For example, I live in Northern Virginia and have a Channel Master
4221 4 Bay Bowtie UHF antenna in my attic. The CM 4221 is a very good
mid-range UHF antenna with a broad pickup towards the front and to the
backside as well. With the CM 4221 aimed at Baltimore, I can get the
Baltimore stations at around 43 miles at an azimuth of 63 degrees and
the closer Washington stations at around 16 miles clumped around 113
degrees in azimuth. That is a 50+ degree spread between the 2 cities. I
also have added a Channel Master 7777 pre-amp to make up for the cable
run and local building obstructions of the top of houses up a slight
hill between my antenna and Baltimore. I also get 5 other stations
scattered around in azimuth.

If you would post your zip code, we can look at your specific
situation and see if maybe a single antenna will do the job. The keep it
simple when possible approach applies to putting up antennas as well.

Alan F

Thanks for all the help! I'm in 98198. Oh, and I originally said ~60
degrees apart, but it should be ~120 degrees. (high school geometry was a
long time ago...)

I'm hoping the problem is my old antenna, with one of the longest conductors
drooping. I have a new one in the garage (a little bit larger than the one
I have now, boom length like 5" longer), but I haven't put it up yet. Snow
around Seattle, probably not a safe time to be on the roof! I'm hoping the
new antenna and a new coax cable will capture more HDTV OTA.

Our current coax cable isn't shielded very well (I think that's how you'd
say it). The copper core is good, then the white plastic cover is okay,
then the foil like material is intact, but the next layer has like 4 wires,
then the black rubbery outer cover. The cable I got from my Dad has more of
a braided layer (instead of the 4-5 wires on our current cable). Is that
shielding or more conductivity? I feel like it would be better
conductivity. The tip is a screw on, instead of a crimp, and when I wiggle
the connector, sometimes I can get NBC in HD, sometimes not. This is my
weekend project, to put up the new antenna and pull the new coax (about
40-50 feet).

NBC, ABC, CBS and a PBS station all broadcast from Seattle. But Fox, WB,
and another PBS station broadcast from Tacoma. I'm hoping to get them all,
since analog broadcasts are supposedly going away in a few years.

Richard


"Alan F" wrote in message
news:[email protected]
Richard Minami wrote:

Hi! Does anyone know if I can run two roof top antennas concurrently? I
live between two metropolitan areas that are about 60 degrees apart. Can
I point one antenna to the north, and then use a splitter to add another
antenna pointing south west? Then I'd run the one cable into my HD
receiver. I've heard that analog signals may ghost because the two
antennas are receiving the signal at different angles. But would a
digital broadcast do the same thing? Thanks!

Combining 2 antennas is usually a tricky project getting 2 directional
antennas aligned just right or a complicated & expensive project involving
jointenna filters.

Depending on the distance to the two sets of broadcast towers, you may be
able to use a single antenna which is a heck of a lot easier and cheaper.
Or just live with the hassle of a rotator. Or 2 antenna lines running down
to the receiver with a remote controlled A/B switch (real pain with
digital receivers and channel scans).

For example, I live in Northern Virginia and have a Channel Master 4221 4
Bay Bowtie UHF antenna in my attic. The CM 4221 is a very good mid-range
UHF antenna with a broad pickup towards the front and to the backside as
well. With the CM 4221 aimed at Baltimore, I can get the Baltimore
stations at around 43 miles at an azimuth of 63 degrees and the closer
Washington stations at around 16 miles clumped around 113 degrees in
azimuth. That is a 50+ degree spread between the 2 cities. I also have
added a Channel Master 7777 pre-amp to make up for the cable run and local
building obstructions of the top of houses up a slight hill between my
antenna and Baltimore. I also get 5 other stations scattered around in
azimuth.

If you would post your zip code, we can look at your specific situation
and see if maybe a single antenna will do the job. The keep it simple when
possible approach applies to putting up antennas as well.

Alan F

In article ,
says...


Hi! Does anyone know if I can run two roof top antennas concurrently? I
live between two metropolitan areas that are about 60 degrees apart. Can I
point one antenna to the north, and then use a splitter to add another
antenna pointing south west? Then I'd run the one cable into my HD
receiver. I've heard that analog signals may ghost because the two antennas
are receiving the signal at different angles. But would a digital broadcast
do the same thing? Thanks!

Two antennas are fine, but I'd use a switch box to switch between them.

whosbest54
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Mac Cool wrote:
G-squared:

You're most certainly mistaken on this one. Digital most certainly
is
sensitive to multipath (ghosts) though it does not show up as a
second
image displaced from the main signal.

Wait, you are agreeing with me and claiming I'm mistaken at the same
time?

I don't think the guy cares what is going inside the receiver, he
wants to
know if the picture will ghost even though he said 'signal' instead
of
picture.
--
Mac Cool

Actually, that IS what I'm saying. The 'mechanism' that causes the
ghosts is reflections adding to the main signal. You said that 'ghosts'
are not a problem but they are. As long as the signal can be equalized
(ghosts removed), the picture will be good but even if the signal is
plenty strong, enough 'ghost' will make it unusable. Bottom line is an
antenna with decent directivity aimed in the right direction will make
all the difference.

GG

The best solution would simply be run separate coax from each antenna
and a
mechanical or electronic switch near the TV. Some TVs have more than
one RF input,
which would eliminate the need for a switch.