On Mon, 16 Feb 2009 00:32:22 -0800, "Sal M. Onella"
wrote:

Many good all-channel antennas exist but the absolute best-performing
antennas are limited to covering one band, sometimes just a portion of one
band. (This idea started a lot of do-it-yourself antenna projects.)

Sure. I can always trade bandwidth for gain. If you only watch one
DTV station, a single channel antenna is a good idea, especially if
it's distant and weak. If you don't like rotators, perhaps a
collection of single channel antennas pointed at each station might be
useful. I live in the mountains where reflections are a problem for
OTA reception. For a time, I was building and selling custom single
channel TV antennas, with built in preamps. They worked great, but
when Comcast started offering $13/month for local only TV, I gave up.

If you determine that you have some stations on VHF and some on UHF,
consider having more than one antenna. In a home where I lived in the
pre-cable days, I had four different antennas.

Same here. Back in the 1970's, I lived in Israel for a while. In the
cities, everyone lived in big apartment complexes. Nobody watched the
official Israeli stations. The good programming was on the various
Arab stations, which were diverse, distant, and politically incorrect.
There was no cable TV (because the government didn't want to make it
easy to watch the Arab stations) so every apartment had its own
collection of antennas. Typical was a 3 meter pole with at least 4
yagis. Multiply that by at least 4 apartments per building and the
roof tops looked like an aluminum forest. Somewhat later, I lived in
Smog Angeles where everything is on Mt Wilson. Only one antenna
needed.

Of note: The bigger the antenna, the more likely it will be highly
directional.

http://groups.google.com/group/rec.radio.amateur.antenna/msg/8535c986a167ac41
"small - efficient - broadband: pick any two."
Roy Lewallen, W7EL

I've dealt with some rather monstrous log periodic directional
antennas. They cover the entire HF spectrum, but only have about 4dBi
of gain at any frequency. Directionality is about what you would
expect for a 4dBi antenna (about 80 degrees -3dB beamwidth). Just
because it's big, doesn't mean it has gain or a narrow beamwidth.

The same thing applies to TV antennas. If you compromise on the
bandwidth by reducing the number of channels it covers, then you can
get some more gain and narrower beamwidth (for a given size). That
seems to be what's happening as the highest frequency goes from 900 to
700MHz. However, that's not going to make a huge difference is size
of gain. More useful is ignoring the VHF channels and making the
antenna UHF only. That really reduces the size of the antenna or
increases the gain (for a given size antenna).

If you expect to receive weak stations from more than one
direction, you'll probably need either a rotator or more than one antenna.

True. I once was involved in building direction finders. I got
greedy and decided to find a commercial application. What the world
needed was a direction finder tied to a rotator and yagi. The yagi
would automatically rotate to the direction of the strongest signal. I
first tried it with a TV antenna and it worked. Unfortunately, my
pre-microprocessor circuitry did not have any way to distinguish
between multiple peaks in the signal strength as well as antenna side
lobes. It would often pick the wrong lobe. Making a 360 degree scan
would solve this problem, but that increased the complexity beyond
acceptable limits.

So, I decided that perhaps it might be useful for commercial two-way
radio. I installed one on a mountain top site on a UHF commercial
frequency. Useful range was dramatically increased for the repeater.
However, during a typical conversation, the antenna would rotate back
and forth between each mobile and base. Commodity antenna rotators
are not designed for near 100% duty cycle. It was also a dice toss as
to whether a mobile could be heard, depending totally on the current
antenna orientation. I could have improved things with a better and
faster motor, but didn't. I know a bad idea when I design one.

I also built an omnidirectional TV antenna designed to be hung near
the top of the local 50 meter redwood and fir trees. There was enough
vertically polarized TV signal to make it usable. However, it also
picked up reflections from every possible direction, resulting in
multiple obnoxious ghosts. Bad idea, but fun to try.

It's probably better to connect multiple antennas through an A/B switch,
rather than combining them.

Yep. If the signals from multiple antenna could just as easily cancel
as they could add. However, if you installed a band pass filter
between the antenna and the combiner, the signals from one channel
will only appear on one port, thus eliminating any chance of
cancellation. I would filter and combine.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:

Same here. Back in the 1970's, I lived in Israel for a while. In the
cities, everyone lived in big apartment complexes. Nobody watched the
official Israeli stations. The good programming was on the various
Arab stations, which were diverse, distant, and politically incorrect.
There was no cable TV (because the government didn't want to make it
easy to watch the Arab stations) so every apartment had its own
collection of antennas. Typical was a 3 meter pole with at least 4
yagis. Multiply that by at least 4 apartments per building and the
roof tops looked like an aluminum forest.

Those days are gone, we have cable TV, DBS TV and streaming video on the
Internet. In the cities the antennas remain, no one wants to pay the money
to remove them. Eventually it will be necessary to repair the roofs under them
and take them down.

We are also supposed to have digital terrestrial TV in a few months, but instead
of each station having various programs, there will be multiple channels
on the same frequency.

Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM

On Mon, 16 Feb 2009 18:24:07 +0000 (UTC), (Geoffrey
S. Mendelson) wrote:

Jeff Liebermann wrote:

Same here. Back in the 1970's, I lived in Israel for a while. In the
cities, everyone lived in big apartment complexes. Nobody watched the
official Israeli stations. The good programming was on the various
Arab stations, which were diverse, distant, and politically incorrect.
There was no cable TV (because the government didn't want to make it
easy to watch the Arab stations) so every apartment had its own
collection of antennas. Typical was a 3 meter pole with at least 4
yagis. Multiply that by at least 4 apartments per building and the
roof tops looked like an aluminum forest.

Those days are gone, we have cable TV, DBS TV and streaming video on the
Internet. In the cities the antennas remain, no one wants to pay the money
to remove them. Eventually it will be necessary to repair the roofs under them
and take them down.

Yes, I know. The real problem with the antenna clutter is that there
was some shading of the ubiquitous solar water heaters also on the
same rooftops. While trying to repair one of the antennas, I stepped
on the glass collector and cracked it. Oops.

Incidentally, I recall that most of the roofs were poured concrete
which could probably withstand a mortar attack. I doubt if they will
require much repair.

While in Israel, I had the bright idea of starting a company to
provide cable TV. I went to the Ministry of the Post (now called
Ministry of Communications), asked about the regulatory details, and
was immediately detained as some manner of spy or subversive.
Apparently, CATV was rather unpopular with the government at the time.
I had to be rescued by my relatives. Sometime in the 1980's, Israel
established the Council for CATV and Satellite Broadcasting, who's
primary purpose was to obstruct deployment. That changed after one of
the changes of government, which suspected that there would be less
rioting in the streets, if people stayed home and watched TV.
http://www.moc.gov.il

At the time, I had been in the US 2way radio biz, so I decided that
Israel might benefit from a commercial radio company. I went back to
the Ministry of the Post, inquired about licensing, and was again
detained as a spy or something. I was again rescued by the relatives.
At the time, during essentially a war time economy, there was no
commercial radio service. That also has changed, but at the time, the
only radio communications was government, military, and ham radio.

We are also supposed to have digital terrestrial TV in a few months, but instead
of each station having various programs, there will be multiple channels
on the same frequency.

We have the same thing here. At this time (before the demise of
analog in June), TV stations are broadcasting one 6 MHz channel of
analog. They were also granted a 2nd 6Mhz channel for digital, which
carries 1 to 4 digital channels. Usually it's a clone of the analog
channel, a Spanish language version, continuous news, and something
else. For a while, one station had one channel with a DTV camera
scanning the scenery around their transmitter building. It was one of
the few things worth watching, but alas, it went away.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
If you don't like rotators, perhaps a
collection of single channel antennas pointed at each station might be
useful.

Are the GPS coordinates for the transmitting antenna
available anywhere? I called the local TV station
and they don't know the coordinates for their
transmitting antenna.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

Are the GPS coordinates for the transmitting antenna
available anywhere? I called the local TV station
and they don't know the coordinates for their
transmitting antenna.

I'd be surprised if they gave them to you if they had them. Publishing the
exact location may be a security risk.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM

Geoffrey S. Mendelson wrote:
Cecil Moore wrote:

Are the GPS coordinates for the transmitting antenna
available anywhere? I called the local TV station
and they don't know the coordinates for their
transmitting antenna.

I'd be surprised if they gave them to you if they had them. Publishing the
exact location may be a security risk.

Geoff.


It's totally a matter of public record. You'd have to be really
paranoid crazy to try to hide something that sends out a Megawatt homing
beacon 24/7.

Geoffrey S. Mendelson wrote:
Cecil Moore wrote:

Are the GPS coordinates for the transmitting antenna
available anywhere? I called the local TV station
and they don't know the coordinates for their
transmitting antenna.

I'd be surprised if they gave them to you if they had them. Publishing the
exact location may be a security risk.

Geoff.


It's totally a matter of public record. You'd have to be really
paranoid crazy to try to hide something that sends out a Megawatt homing
beacon 24/7.

Geoffrey S. Mendelson wrote:
I'd be surprised if they gave them to you if they had them. Publishing the
exact location may be a security risk.

Then how can I aim my antenna while on top of a tower
with no one to assist me?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Geoffrey S. Mendelson wrote:
I'd be surprised if they gave them to you if they had them. Publishing the
exact location may be a security risk.

Then how can I aim my antenna while on top of a tower
with no one to assist me?

However a location such as" 5 miles east of town on the Interstate"
is good enough to aim the antenna, but may be obscure enough to prevent
vandalism, theft, etc.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM

In message , Geoffrey S.
Mendelson writes
Cecil Moore wrote:
Geoffrey S. Mendelson wrote:
I'd be surprised if they gave them to you if they had them. Publishing the
exact location may be a security risk.

Then how can I aim my antenna while on top of a tower
with no one to assist me?

However a location such as" 5 miles east of town on the Interstate"
is good enough to aim the antenna, but may be obscure enough to prevent
vandalism, theft, etc.

It's pretty hard to keep secret the location of (say) a 1000 foot TV
transmitter mast!
--
Ian