One more antenna question: Antenna pitch?

[mm]

One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

It would fit more easily in the attic if I pointed it down a little
bit just like the roof pitches down from the center. Does the angle
of the axis matter that much if the individual elements are all
horizontal?

After all, if the tranmitter is higher than the antenna, it's as if
even a horizontal antenna is pointed down, from the pov of the
transmitter.

I've been reading but nothing has addressed this. All outdoor
antennas are of course horizontal, and I don't get to see people's
indoor antennas.




BTW, as to loss of signal in an attic,
http://www.dennysantennaservice.com/TV_Antenna_Attic_Installation.html
says: "A plywood roof covered by a single layer of asphalt shingles is
best.", (that is, other roofs are worse) and that's just what I have.
I'm sure it would still work better on the roof, but if I lose one or
two stations, I can accept that.

 

[Arfa Daily]

"mm" <NOPSAMmm2005@bigfoot.com> wrote in message
news:m2h9h5hpvfr698nd2o32r7klio82r3g7q5@4ax.com...

One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

It would fit more easily in the attic if I pointed it down a little
bit just like the roof pitches down from the center. Does the angle
of the axis matter that much if the individual elements are all
horizontal?

After all, if the tranmitter is higher than the antenna, it's as if
even a horizontal antenna is pointed down, from the pov of the
transmitter.

I've been reading but nothing has addressed this. All outdoor
antennas are of course horizontal, and I don't get to see people's
indoor antennas.

That's an interesting question. I guess to some extent, it depends on the
frequency involved, and how close you are to the transmitter. I feel that
the potential losses are likely to be far worse at UHF than VHF. An example
that comes to mind is my local ATV repeater. It is sited on a hill, and I
clearly remember some of us helping out a new licensee, who was located
within line of sight of the transmitter mast, about 3/4 mile away, and at
the bottom of the hill. He could barely pick up a signal from it, and could
not access it with his own 2W transmitter at all. This was at 23cms (1.2GHz)
so a little above the top of the UHF band. We did some field strength
checks, and found that there was quite a distinct 'shadow' around the
transmitter site, out to a distance of around a mile. The repeater's antenna
is a slotted waveguide.

The first thing that we did was to re-site his antenna pair onto a taller
mast, which produced a significant improvement to his situation, but was
still not good, considering how close he was to the repeater. The final
thing that we did was to tilt his antennas up at a similar angle to the hill
itself, and this brought about the improvement to solid P5 copy and repeater
access, that we had been expecting. I believe I have read that it is common
to find this shadowing effect around high power TV transmitter masts, and
that it can extend out to several miles in some instances. Michael T could
probably comment better on this as he was involved in the industry.

So, I suppose that on paper, the answer has to be that there will be an
effect on received signal strength with the antenna tilted down, but it will
probably not be enough to notice on a modern TV set, if the signal is not
marginal and hovering on the set's AGC threshold in the first place. If you
take it to its logical conclusion, if you stood the antenna on its 'nose',
it would receive virtually nothing. At some point, horizontal or pointing
slightly *up*, you would be receiving a maximum signal. Anywhere inbetween
must, in theory at least, be less than the potential maximum.

Of course, now we're talking digital TV transmissions, all bets are off on
this ...

Arfa

 

[Meat Plow]

On Tue, 01 Dec 2009 02:46:53 -0500, mm
<NOPSAMmm2005@bigfoot.com>wrote:

One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

It would fit more easily in the attic if I pointed it down a little
bit just like the roof pitches down from the center. Does the angle
of the axis matter that much if the individual elements are all
horizontal?

After all, if the tranmitter is higher than the antenna, it's as if
even a horizontal antenna is pointed down, from the pov of the
transmitter.

I've been reading but nothing has addressed this. All outdoor
antennas are of course horizontal, and I don't get to see people's
indoor antennas.

http://www.antenna-theory.com/
http://www.classictesla.com/download/emfields.pdf
http://www.aerialsandtv.com/tvaerialtests.html

 

[hr(bob) hofmann@att.net]

On Dec 1, 3:42 am, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

"mm" <NOPSAMmm2...@bigfoot.com> wrote in message

news:m2h9h5hpvfr698nd2o32r7klio82r3g7q5@4ax.com...





One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

It would fit more easily in the attic if I pointed it down a little
bit just like the roof pitches down from the center.  Does the angle
of the axis matter that much if the individual elements are all
horizontal?

After all, if the tranmitter is higher than the antenna, it's as if
even a horizontal antenna is pointed down, from the pov of the
transmitter.

I've been reading but nothing has addressed this.   All outdoor
antennas are of course horizontal, and I don't get to see people's
indoor antennas.

That's an interesting question. I guess to some extent, it depends on the
frequency involved, and how close you are to the transmitter. I feel that
the potential losses are likely to be far worse at UHF than VHF. An example
that comes to mind is my local ATV repeater. It is sited on a hill, and I
clearly remember some of us helping out a new licensee, who was located
within line of sight of the transmitter mast, about 3/4 mile away, and at
the bottom of the hill. He could barely pick up a signal from it, and could
not access it with his own 2W transmitter at all. This was at 23cms (1.2GHz)
so a little above the top of the UHF band. We did some field strength
checks, and found that there was quite a distinct 'shadow' around the
transmitter site, out to a distance of around a mile. The repeater's antenna
is a slotted waveguide.

The first thing that we did was to re-site his antenna pair onto a taller
mast, which produced a significant improvement to his situation, but was
still not good, considering how close he was to the repeater. The final
thing that we did was to tilt his antennas up at a similar angle to the hill
itself, and this brought about the improvement to solid P5 copy and repeater
access, that we had been expecting. I believe I have read that it is common
to find this shadowing effect around high power TV transmitter masts, and
that it can extend out to several miles in some instances. Michael T could
probably comment better on this as he was involved in the industry.

So, I suppose that on paper, the answer has to be that there will be an
effect on received signal strength with the antenna tilted down, but it will
probably not be enough to notice on a modern TV set, if the signal is not
marginal and hovering on the set's AGC threshold in the first place. If you
take it to its logical conclusion, if you stood the antenna on its 'nose',
it would receive virtually nothing. At some point, horizontal or pointing
slightly *up*, you would be receiving a maximum signal. Anywhere inbetween
must, in theory at least, be less than the potential maximum.

Of course, now we're talking digital TV transmissions, all bets are off on
this ...  

Arfa- Hide quoted text -

- Show quoted text -

Digital signals travel through space the same as analog signals at the
same frequency. The best reception is for the antenna to point
directly at the transmitter. If there are reflections, then pointing
either upward or downward from the transmitter maight improve
reception. Digital formatting of the signal may make reflections more
or less of a problem than it was with older analog signal format.

 

[whit3rd]

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:

One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

Yes, it matters; the main part of that long antenna is 'director'
elements, which create a kind of shadow on the active
dipole. The rays get past if you aren't roughly lined up with
the line-of-sight to the transmitter.

Also, such a long antenna has high 'gain' which means it
MUST be aimed carefully; how can you possibly adjust it
if it's bumping into the roof?

 

[Arfa Daily]

"hr(bob) hofmann@att.net" <hrhofmann@att.net> wrote in message
news:8542c2ef-9ef7-4ef3-82c2-7739c1766a1a@v25g2000yqk.googlegroups.com...
On Dec 1, 3:42 am, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

"mm" <NOPSAMmm2...@bigfoot.com> wrote in message

news:m2h9h5hpvfr698nd2o32r7klio82r3g7q5@4ax.com...





One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

It would fit more easily in the attic if I pointed it down a little
bit just like the roof pitches down from the center. Does the angle
of the axis matter that much if the individual elements are all
horizontal?

After all, if the tranmitter is higher than the antenna, it's as if
even a horizontal antenna is pointed down, from the pov of the
transmitter.

I've been reading but nothing has addressed this. All outdoor
antennas are of course horizontal, and I don't get to see people's
indoor antennas.

That's an interesting question. I guess to some extent, it depends on the
frequency involved, and how close you are to the transmitter. I feel that
the potential losses are likely to be far worse at UHF than VHF. An
example
that comes to mind is my local ATV repeater. It is sited on a hill, and I
clearly remember some of us helping out a new licensee, who was located
within line of sight of the transmitter mast, about 3/4 mile away, and at
the bottom of the hill. He could barely pick up a signal from it, and
could
not access it with his own 2W transmitter at all. This was at 23cms
(1.2GHz)
so a little above the top of the UHF band. We did some field strength
checks, and found that there was quite a distinct 'shadow' around the
transmitter site, out to a distance of around a mile. The repeater's
antenna
is a slotted waveguide.

The first thing that we did was to re-site his antenna pair onto a taller
mast, which produced a significant improvement to his situation, but was
still not good, considering how close he was to the repeater. The final
thing that we did was to tilt his antennas up at a similar angle to the
hill
itself, and this brought about the improvement to solid P5 copy and
repeater
access, that we had been expecting. I believe I have read that it is
common
to find this shadowing effect around high power TV transmitter masts, and
that it can extend out to several miles in some instances. Michael T could
probably comment better on this as he was involved in the industry.

So, I suppose that on paper, the answer has to be that there will be an
effect on received signal strength with the antenna tilted down, but it
will
probably not be enough to notice on a modern TV set, if the signal is not
marginal and hovering on the set's AGC threshold in the first place. If
you
take it to its logical conclusion, if you stood the antenna on its 'nose',
it would receive virtually nothing. At some point, horizontal or pointing
slightly *up*, you would be receiving a maximum signal. Anywhere inbetween
must, in theory at least, be less than the potential maximum.

Of course, now we're talking digital TV transmissions, all bets are off on
this ...

Arfa- Hide quoted text -

- Show quoted text -

Digital signals travel through space the same as analog signals at the
same frequency. The best reception is for the antenna to point
directly at the transmitter. If there are reflections, then pointing
either upward or downward from the transmitter maight improve
reception. Digital formatting of the signal may make reflections more
or less of a problem than it was with older analog signal format.


I see that you're well into all the media and government hype about how good
digital terrestrial TV is then, Bob ...

The (tongue in cheek) point I was making had nothing to do with the format
of the modulating signal, which of course has absolutely nothing to do with
how well or otherwise, the carrier propagates through space. I was actually
referring to less-than-ideal reception circumstances such as those the OP
suggests that he may have, which with an analogue signal, may well give
perfectly acceptable results, but with a digital signal might result in
digital cliff pixellation and freezing. Digital terrestrial TV signals are,
in my experience here in the UK, nothing like as robust, or easily received
in many transmission regions, as the government - whose primary interest
lies in how much money they can make by selling off large chunks of the UHF
TV band to cell phone operators - would have Joe public believe through
their hyped-up and often misleading media campaign directed at the subject
....

Arfa

 

[hr(bob) hofmann@att.net]

On Dec 1, 7:30 pm, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

"hr(bob) hofm...@att.net" <hrhofm...@att.net> wrote in message

news:8542c2ef-9ef7-4ef3-82c2-7739c1766a1a@v25g2000yqk.googlegroups.com...
On Dec 1, 3:42 am, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:





"mm" <NOPSAMmm2...@bigfoot.com> wrote in message

news:m2h9h5hpvfr698nd2o32r7klio82r3g7q5@4ax.com...

One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

It would fit more easily in the attic if I pointed it down a little
bit just like the roof pitches down from the center. Does the angle
of the axis matter that much if the individual elements are all
horizontal?

After all, if the tranmitter is higher than the antenna, it's as if
even a horizontal antenna is pointed down, from the pov of the
transmitter.

I've been reading but nothing has addressed this. All outdoor
antennas are of course horizontal, and I don't get to see people's
indoor antennas.

That's an interesting question. I guess to some extent, it depends on the
frequency involved, and how close you are to the transmitter. I feel that
the potential losses are likely to be far worse at UHF than VHF. An
example
that comes to mind is my local ATV repeater. It is sited on a hill, and I
clearly remember some of us helping out a new licensee, who was located
within line of sight of the transmitter mast, about 3/4 mile away, and at
the bottom of the hill. He could barely pick up a signal from it, and
could
not access it with his own 2W transmitter at all. This was at 23cms
(1.2GHz)
so a little above the top of the UHF band. We did some field strength
checks, and found that there was quite a distinct 'shadow' around the
transmitter site, out to a distance of around a mile. The repeater's
antenna
is a slotted waveguide.

The first thing that we did was to re-site his antenna pair onto a taller
mast, which produced a significant improvement to his situation, but was
still not good, considering how close he was to the repeater. The final
thing that we did was to tilt his antennas up at a similar angle to the
hill
itself, and this brought about the improvement to solid P5 copy and
repeater
access, that we had been expecting. I believe I have read that it is
common
to find this shadowing effect around high power TV transmitter masts, and
that it can extend out to several miles in some instances. Michael T could
probably comment better on this as he was involved in the industry.

So, I suppose that on paper, the answer has to be that there will be an
effect on received signal strength with the antenna tilted down, but it
will
probably not be enough to notice on a modern TV set, if the signal is not
marginal and hovering on the set's AGC threshold in the first place. If
you
take it to its logical conclusion, if you stood the antenna on its 'nose',
it would receive virtually nothing. At some point, horizontal or pointing
slightly *up*, you would be receiving a maximum signal. Anywhere inbetween
must, in theory at least, be less than the potential maximum.

Of course, now we're talking digital TV transmissions, all bets are off on
this ...

Arfa- Hide quoted text -

- Show quoted text -

Digital signals travel through space the same as analog signals at the
same frequency.  The best reception is for the antenna to point
directly at the transmitter.  If there are reflections, then pointing
either upward or downward from the transmitter maight improve
reception.  Digital formatting of the signal may make reflections more
or less of a problem than it was with older analog  signal format.

I see that you're well into all the media and government hype about how good
digital terrestrial TV is then, Bob ...

The (tongue in cheek) point I was making had nothing to do with the format
of the modulating signal, which of course has absolutely nothing to do with
how well or otherwise, the carrier propagates through space. I was actually
referring to less-than-ideal reception circumstances such as those the OP
suggests that he may have, which with an analogue signal, may well give
perfectly acceptable results, but with a digital signal might result in
digital cliff pixellation and freezing. Digital terrestrial TV signals are,
in my experience here in the UK, nothing like as robust, or easily received
in many transmission regions, as the government - whose primary interest
lies in how much money they can make by selling off large chunks of the UHF
TV band to cell phone operators - would have Joe public believe through
their hyped-up and often misleading media campaign directed at the subject
...

Arfa- Hide quoted text -

- Show quoted text -

I agree with everything you said. People tolerate ghosting much
better than digital receivers do. I have two digital convertors that
I play with, but my household tv is on a cable system that a couple of
months ago converted to a special digital transmission on the cable,
not the same as the on-the-air digital system that I use the 2
convertors for..

When we had wet weather, I would lose digital reception on any/all
combinations of the 3 digital cable convertors that my cable company
provided. I complained and got one unit replaced, but still had the
problems. I complained again and they sent a "trained" repairman
out. He immediately said it was my internal house cable distribution
system that was at fault. I replied that unless my house had a bad
roof leak, there was no way that the weather should affect my cable
reception. He finally went out to the telephone pole in my back yard
where the cable came out of the ground and went up the pole to a tap
on their cable. There he discovered, right at the tap, that a
friendly squirrel had chewed through the outside weatherproofing and
that water was getting into the cable. A new drop from the pole to
the house solved the problem, and hopefully when the next squirrel
gets hungry I won't have such a problem getting things fixed.

I did tv repair work in the 1950's to put myself through college and
worked on color tv right after the FCC dropped the CBS color wheel in
favor of the RCA system. Almost worked at Hazeltine Labs because they
acquired many of the RCA color tv patents, but Bell Labs offered to
pay for me to get my Master's degree and so I ended up at Bell Labs.
Was there for 44 years and loved every minute of it. Ended up in EMC
work which was a great adventure as no two days were ever the same.

 

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:

One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

It would fit more easily in the attic if I pointed it down a little
bit just like the roof pitches down from the center.  Does the angle
of the axis matter that much if the individual elements are all
horizontal?  

After all, if the tranmitter is higher than the antenna, it's as if
even a horizontal antenna is pointed down, from the pov of the
transmitter.

I've been reading but nothing has addressed this.   All outdoor
antennas are of course horizontal, and I don't get to see people's
indoor antennas.

BTW, as to loss of signal in an attic,http://www.dennysantennaservice.com/TV_Antenna_Attic_Installation.html
says: "A plywood roof covered by a single layer of asphalt shingles is
best.", (that is, other roofs are worse) and that's just what I have.
I'm sure it would still work better on the roof, but if I lose one or
two stations, I can accept that.

You don't want or need a 13 ft beastly antenna that can get channels
2-6. This little guy will be much easier to handle in the attic
(though it's better outside) and has reasonable gain. Don't jet
fighters release 'chaff' to screw up the enemy? Seems a lot like nails
suspended in sheets of plywood. That's one reason to be outside of the
'chaff'.

http://www.winegard.com/kbase/upload/HD7694P.pdf

BTW there are no channels >51 any more.

G˛

 

[baron]

Arfa Daily Inscribed thus:

I was actually referring to less-than-ideal reception
circumstances such as those the OP suggests that he may have, which
with an analogue signal, may well give perfectly acceptable results,
but with a digital signal might result in digital cliff pixellation
and freezing. Digital terrestrial TV signals are, in my experience
here in the UK, nothing like as robust, or easily received in many
transmission regions, as the government - whose primary interest lies
in how much money they can make by selling off large chunks of the UHF
TV band to cell phone operators - would have Joe public believe
through their hyped-up and often misleading media campaign directed at
the subject ...

Arfa

Well Said !
Yet another make the people pay Government scheme, among other things.

--
Best Regards:
Baron.

 

[mm]

On Tue, 1 Dec 2009 14:35:23 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:
One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

Yes, it matters; the main part of that long antenna is 'director'
elements, which create a kind of shadow on the active
dipole. The rays get past if you aren't roughly lined up with
the line-of-sight to the transmitter.

Also, such a long antenna has high 'gain' which means it
MUST be aimed carefully; how can you possibly adjust it
if it's bumping into the roof?

I may be confused about what "gain" is. Why would a high gain antenna
have to be aimed carefully? If it has high gain, it seems like it
would have some gain to spare if it were badly aimed.

If it had low gain, it seems like it would have to be aimed precisely.

 

[Sjouke Burry]

mm wrote:

On Tue, 1 Dec 2009 14:35:23 -0800 (PST), whit3rd <whit3rd@gmail.com
wrote:

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:
One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.
Yes, it matters; the main part of that long antenna is 'director'
elements, which create a kind of shadow on the active
dipole. The rays get past if you aren't roughly lined up with
the line-of-sight to the transmitter.

Also, such a long antenna has high 'gain' which means it
MUST be aimed carefully; how can you possibly adjust it
if it's bumping into the roof?

I may be confused about what "gain" is. Why would a high gain antenna
have to be aimed carefully? If it has high gain, it seems like it
would have some gain to spare if it were badly aimed.

If it had low gain, it seems like it would have to be aimed precisely.

High gain means "narrow bundle" , so a high gain antenna needs

careful aiming.

 

[mm]

On Wed, 02 Dec 2009 20:26:45 +0100, Sjouke Burry
<burrynulnulfour@ppllaanneett.nnll> wrote:

mm wrote:
On Tue, 1 Dec 2009 14:35:23 -0800 (PST), whit3rd <whit3rd@gmail.com
wrote:

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:
One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.
Yes, it matters; the main part of that long antenna is 'director'
elements, which create a kind of shadow on the active
dipole. The rays get past if you aren't roughly lined up with
the line-of-sight to the transmitter.

Also, such a long antenna has high 'gain' which means it
MUST be aimed carefully; how can you possibly adjust it
if it's bumping into the roof?

I may be confused about what "gain" is. Why would a high gain antenna
have to be aimed carefully? If it has high gain, it seems like it
would have some gain to spare if it were badly aimed.

If it had low gain, it seems like it would have to be aimed precisely.

High gain means "narrow bundle" , so a high gain antenna needs
careful aiming.

So what aobut people on mountains and in valleys, where the
transmitter is lower or higher than they are. Should their antennas
be tipped down or up to aim at the transimitting antenna?

I never hear anyone recommend that, and afaicr (and I don't spend much
time near mountains, but some), every outdoor antenna I've ever seen
has been horizontal.

 

[Dave Platt]

In article <credh5h6bdj6rmo53au6lg4en8q88vtrpe@4ax.com>,
mm <NOPSAMmm2005@bigfoot.com> wrote:

I may be confused about what "gain" is. Why would a high gain antenna
have to be aimed carefully? If it has high gain, it seems like it
would have some gain to spare if it were badly aimed.

If it had low gain, it seems like it would have to be aimed precisely.

Let's drop back a few yards and punt a bit.

Antennas are sensitive to incoming RF (and convert it into an
electrical flow) because the RF induces current flow in the antenna
elements. Similarly, if you push power into an antenna (as a
transmitter does), the current flow in the elements causes power to be
converted from electrical current into RF electromagnetic fields.
These fields propagate away from the antenna in all directions.

There's a famous principle in radio known as the Reciprocity Rule. It
means, basically, that an antenna's pattern of RF power transmission
(when transmitting), and the antenna's pattern of sensitivity to
incoming RF, are identical.

Consider the most basic, primitive sort of antenna which one can
conceive of. It's equally sensitive to RF arriving from any
direction, and when fed power from a transmitter it transmits an
equal amount of power in all directions. Looked at in a graphical
sense, the transmitted power pattern is a perfect sphere (and so is
the receive sensitivity pattern).

This is referred to as an "isotropic" antenna. It's a purely
theoretical antenna - no real, physical antenna of any sort can be
truly isotropic.

All real antennas have a directional sensitivity to RF - they're more
sensitive to RF coming from some directions than from others, and they
tend to radiate more power (when transmitting) in some directions than
in others.

When one talks about the "gain" of an antenna, one is talking about a
ratio.

amount of power transmitted in the "best" direction
Gain = ---------------------------------------------------
power transmitted by an isotropic direction

This figure is usually expressed in decibels - take the base-10
logarithm of the numerical radio, and multiply by 10. A gain of 10 dBi
means that the antenna is transmitting 10 times more power (in its
best direction) than an isotropic antenna would. 20 dBi means it's
transmitting 100 times more power than an isotropic antenna would.

Now, when transmitting, it should be clear that the antenna cannot
possibly radiate more power than it's being fed by the transmitter.
It's not an amplifier or an energy-creator - it's just an energy
*transformer*. So, when the antenna has gain over an isotropic
antenna, and is transmitting more power in one direction than an
isotropic antenna would... and yet the *total* power being radiated is
the same... this means that the antenna must necessarily be
transmitting *less* power than an isotropic antenna in some other
directions.

Similarly, this antenna will be more sensitive (to received signals)
than an isotropic antenna, *if* the signals are arriving from the
favored direction. Since the transmit and receive patterns are the
same (per the reciprocity rule), the antenna will be *less* sensitive
than an isotropic to incoming signals from other directions.

In effect, what antenna gain is "doing", is taking the perfectly
spherical sensitivity pattern of an isotropic antenna, and "squashing"
it like a balloon full of water... it ends up being squeezed in some
places (less sensitivity) and bulging out in other places (higher
sensitivity).

The most basic "squashing" occurs with the simple dipole antenna -
just a single half-wavelength element. The pattern for a dipole looks
rather like a donut (rather than a sphere) - it's squashed above and
below, and bulges out a bit towards the horizon. A dipole antenna has
a gain of 2.15 dBi, plus or minus a bit.

[Some antenna designers describe their antenna gains as "gain, compares
to that of a half-wave dipole" - this ratio in decibels is called
"dBd". Other designers use dBi (ratio compared to an isotropic),
because the figure in dBi is always 2.15 larger than the equivalent
figure in dBd, and it makes the marketing easier :-]

The pattern for a typical TV antenna looks a bit like a searchlight
beam... it bulges out far towards the horizon in one direction, and is
doesn't come out very far at all in other directions. The higher the
gain, the narrower (and further-out-sticking) the bulge towards the
horizon.

That's the problem with a really high-gain antenna. Of necessity, its
sensitivity pattern has a narrow lobe... if you turn it more than a
small amount away from the transmitter, then the transmitter falls
outside the main lobe, and you can get *less* signal out of the
antenna than you'd get with a lower-gain antenna (having a broader
sensitivity pattern).

You pay your money and you take your choice... high gain (and narrow
directional sensitivity) or lower gain (but a wider pattern). People
out in a "deep fringe" reception area sometimes don't have a choice...
they must use a high-gain antenna, and aim it very precisely (often
with the aid of a remote-controlled antenna rotator).

Folks in most urban and suburban areas can usually get by with a
lower-gain, broader-pattern antenna.

Now, things get tricker if you start adding *electrical* gain to the
system, by adding an amplifier between the antenna and the TV. This
electrical gain will increase the antenna's system's output equally,
for signals arriving from any direction. This may be good, bad, or
indifferent, depending on the specifics of your actual situation...
amplifiers will also amplify incoming noise and interference, they
always add some noise of their own, and if they're hit by a strong
signal they can overload themselves or overload the TV set and
actually reduce the signal quality.

http://en.wikipedia.org/wiki/Dipole_antenna has further information,
if you want to go into it in more depth.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[Sjouke Burry]

mm wrote:

On Wed, 02 Dec 2009 20:26:45 +0100, Sjouke Burry
burrynulnulfour@ppllaanneett.nnll> wrote:

mm wrote:
On Tue, 1 Dec 2009 14:35:23 -0800 (PST), whit3rd <whit3rd@gmail.com
wrote:

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:
One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.
Yes, it matters; the main part of that long antenna is 'director'
elements, which create a kind of shadow on the active
dipole. The rays get past if you aren't roughly lined up with
the line-of-sight to the transmitter.

Also, such a long antenna has high 'gain' which means it
MUST be aimed carefully; how can you possibly adjust it
if it's bumping into the roof?
I may be confused about what "gain" is. Why would a high gain antenna
have to be aimed carefully? If it has high gain, it seems like it
would have some gain to spare if it were badly aimed.

If it had low gain, it seems like it would have to be aimed precisely.

High gain means "narrow bundle" , so a high gain antenna needs
careful aiming.

So what aobut people on mountains and in valleys, where the
transmitter is lower or higher than they are. Should their antennas
be tipped down or up to aim at the transimitting antenna?

I never hear anyone recommend that, and afaicr (and I don't spend much
time near mountains, but some), every outdoor antenna I've ever seen
has been horizontal.
It turns a little bit into nit picking, but Yes try to aim

as accurately as possible at the transmitter, especially with
multi-element antennas.
And keep in mind,that an antenna cannot look through a big hill
or a mountain. And only with some difficulty through your house/roof
or that of the neighbour.
For the hill/mountain, you might need a repeater on that hill/mountain top.
Or try to find a reliable reflection around those obstacles.
In my country the digital tv is polarized vertically, so although we
can use the same old antennas, they have to be turned on their sides,
and vertical aim is even more important.

 

[mm]

On Wed, 2 Dec 2009 01:44:24 -0800 (PST), stratus46@yahoo.com wrote:

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:
One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

It would fit more easily in the attic if I pointed it down a little
bit just like the roof pitches down from the center.  Does the angle
of the axis matter that much if the individual elements are all
horizontal?  

After all, if the tranmitter is higher than the antenna, it's as if
even a horizontal antenna is pointed down, from the pov of the
transmitter.

I've been reading but nothing has addressed this.   All outdoor
antennas are of course horizontal, and I don't get to see people's
indoor antennas.

BTW, as to loss of signal in an attic,http://www.dennysantennaservice.com/TV_Antenna_Attic_Installation.html
says: "A plywood roof covered by a single layer of asphalt shingles is
best.", (that is, other roofs are worse) and that's just what I have.
I'm sure it would still work better on the roof, but if I lose one or
two stations, I can accept that.

You don't want or need a 13 ft beastly antenna that can get channels
2-6.

I thought this one didn't get 2-6, but I should go check again.

This little guy will be much easier to handle in the attic
(though it's better outside) and has reasonable gain. Don't jet
fighters release 'chaff' to screw up the enemy? Seems a lot like nails
suspended in sheets of plywood. That's one reason to be outside of the
'chaff'.

Good point. Not only that, the roofer used nails that are a lot
longer for the second roof than they had used for the first roof. And
my hair isn't as thick as it used to be if that matters, but I'm more
afraid I'm going to jab my head then I used to be.

http://www.winegard.com/kbase/upload/HD7694P.pdf

BTW there are no channels >51 any more.

Thanks a lot.

>G˛

 

[mm]

On Wed, 02 Dec 2009 23:46:06 +0100, Sjouke Burry
<burrynulnulfour@ppllaanneett.nnll> wrote:

mm wrote:
On Wed, 02 Dec 2009 20:26:45 +0100, Sjouke Burry
burrynulnulfour@ppllaanneett.nnll> wrote:

mm wrote:
On Tue, 1 Dec 2009 14:35:23 -0800 (PST), whit3rd <whit3rd@gmail.com
wrote:

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:
One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.
Yes, it matters; the main part of that long antenna is 'director'
elements, which create a kind of shadow on the active
dipole. The rays get past if you aren't roughly lined up with
the line-of-sight to the transmitter.

Also, such a long antenna has high 'gain' which means it
MUST be aimed carefully; how can you possibly adjust it
if it's bumping into the roof?
I may be confused about what "gain" is. Why would a high gain antenna
have to be aimed carefully? If it has high gain, it seems like it
would have some gain to spare if it were badly aimed.

If it had low gain, it seems like it would have to be aimed precisely.

High gain means "narrow bundle" , so a high gain antenna needs
careful aiming.

So what aobut people on mountains and in valleys, where the
transmitter is lower or higher than they are. Should their antennas
be tipped down or up to aim at the transimitting antenna?

I never hear anyone recommend that, and afaicr (and I don't spend much
time near mountains, but some), every outdoor antenna I've ever seen
has been horizontal.
It turns a little bit into nit picking, but Yes try to aim
as accurately as possible at the transmitter, especially with
multi-element antennas.
And keep in mind,that an antenna cannot look through a big hill
or a mountain. And only with some difficulty through your house/roof
or that of the neighbour.
For the hill/mountain, you might need a repeater on that hill/mountain top.
Or try to find a reliable reflection around those obstacles.
In my country the digital tv is polarized vertically, so although we
can use the same old antennas, they have to be turned on their sides,
and vertical aim is even more important.

Very interesting. Really

What about places where there is line of sight between the
transmitting antenna and the home antenna, but the home is a lot lower
or higher than than the T-antenna. Does the home antenna need to be
tipped up to point to a transmitting antenna that's higher? It sounds
like that follows from what was said ealier in this thread, but I've
never seeen it done or recommended.

 

[Sjouke Burry]

mm wrote:

On Wed, 02 Dec 2009 23:46:06 +0100, Sjouke Burry
burrynulnulfour@ppllaanneett.nnll> wrote:

mm wrote:
On Wed, 02 Dec 2009 20:26:45 +0100, Sjouke Burry
burrynulnulfour@ppllaanneett.nnll> wrote:

mm wrote:
On Tue, 1 Dec 2009 14:35:23 -0800 (PST), whit3rd <whit3rd@gmail.com
wrote:

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:
One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.
Yes, it matters; the main part of that long antenna is 'director'
elements, which create a kind of shadow on the active
dipole. The rays get past if you aren't roughly lined up with
the line-of-sight to the transmitter.

Also, such a long antenna has high 'gain' which means it
MUST be aimed carefully; how can you possibly adjust it
if it's bumping into the roof?
I may be confused about what "gain" is. Why would a high gain antenna
have to be aimed carefully? If it has high gain, it seems like it
would have some gain to spare if it were badly aimed.

If it had low gain, it seems like it would have to be aimed precisely.

High gain means "narrow bundle" , so a high gain antenna needs
careful aiming.
So what aobut people on mountains and in valleys, where the
transmitter is lower or higher than they are. Should their antennas
be tipped down or up to aim at the transimitting antenna?

I never hear anyone recommend that, and afaicr (and I don't spend much
time near mountains, but some), every outdoor antenna I've ever seen
has been horizontal.
It turns a little bit into nit picking, but Yes try to aim
as accurately as possible at the transmitter, especially with
multi-element antennas.
And keep in mind,that an antenna cannot look through a big hill
or a mountain. And only with some difficulty through your house/roof
or that of the neighbour.
For the hill/mountain, you might need a repeater on that hill/mountain top.
Or try to find a reliable reflection around those obstacles.
In my country the digital tv is polarized vertically, so although we
can use the same old antennas, they have to be turned on their sides,
and vertical aim is even more important.

Very interesting. Really

What about places where there is line of sight between the
transmitting antenna and the home antenna, but the home is a lot lower
or higher than than the T-antenna. Does the home antenna need to be
tipped up to point to a transmitting antenna that's higher? It sounds
like that follows from what was said ealier in this thread, but I've
never seeen it done or recommended.
Well, you aim carefully at the horizon, and hope that enough radiation

is following the earth surface.
Some bending down always occurs, and hopefully for you it is enough.

 

[Dave Platt]

What about places where there is line of sight between the
transmitting antenna and the home antenna, but the home is a lot lower
or higher than than the T-antenna. Does the home antenna need to be
tipped up to point to a transmitting antenna that's higher? It sounds
like that follows from what was said ealier in this thread, but I've
never seeen it done or recommended.

You may get a slight increase in signal by uptilting the receive
antenna.

However, this is hard to predict, and usually not a terribly
significant factor, for two reasons:

(1) The amount of up-tilt you would need is not likely, in most cases,
to be more than a few degrees. It's probably less than the
"half-power vertical beam-width" of a typical TV antenna... likely
quite a lot less.

If, for example, the transmitting antenna is only 2 or 3 degrees
above the horizon, and the receiving antenna's vertical pattern
has a half-power beamwidth of 10 degrees or more (which would be
the case for all but the longest, highest-gain TV antennas), then
the amount of power you'd be giving up by not uptilting the
antenna is negligible.

(2) The signal path from the transmitter to your antenna is
complicated by reflections off of the ground, nearby buildings,
hills, and so forth. You might actually find a higher-quality
signal by pointing your antenna slightly away from the transmitter,
if by doing so you picked up a particularly strong reflection, or
_avoided_ picking up a side reflection which was causing multipath
distortion.

The cases in which an antenna needs to be pointed very exactly (both
horizontally and vertically), are those in which it has a very high
gain and thus a narrow beamwidth. How often will you be far enough
away from a transmitter that you need an antenna with this much gain,
*and* be so far below it that its position is a significant distance
above the horizon and would need to tilt it up by more than a few
degrees?

I don't think this combination of circumstances is at all common. If
it's close enough and high enough that it's far above the horizon,
then you're almost certainly able to use a low-gain antenna with a
very broad vertical pattern, and will get plenty of signal.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

On Tue, 01 Dec 2009 02:46:53 -0500, mm <NOPSAMmm2005@bigfoot.com>
wrote:

One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.

It would fit more easily in the attic if I pointed it down a little
bit just like the roof pitches down from the center. Does the angle
of the axis matter that much if the individual elements are all
horizontal?

After all, if the tranmitter is higher than the antenna, it's as if
even a horizontal antenna is pointed down, from the pov of the
transmitter.

I've been reading but nothing has addressed this. All outdoor
antennas are of course horizontal, and I don't get to see people's
indoor antennas.

A small amount of tilt won't make a significant difference. Those that
suggest tilting the antenna will increase the gain are misguided. The
antenna can take advantage of ground reflection up to a theoretical
6db of gain. This gain is seldom reached but the in phase reflected e
field that causes this gain is best achieved when the antenna is
horizontal.

 

[GregS]

In article <5ildh5p6gar3opkg9dciq1otdci8flutjk@4ax.com>, mm <NOPSAMmm2005@bigfoot.com> wrote:

On Wed, 02 Dec 2009 20:26:45 +0100, Sjouke Burry
burrynulnulfour@ppllaanneett.nnll> wrote:

mm wrote:
On Tue, 1 Dec 2009 14:35:23 -0800 (PST), whit3rd <whit3rd@gmail.com
wrote:

On Nov 30, 11:46 pm, mm <NOPSAMmm2...@bigfoot.com> wrote:
One more antenna question: Antenna pitch?

That is, my attic has a pitched roof and the antenna for channels 7 to
60 that I'm thinking of now is almost 13 feet long.
Yes, it matters; the main part of that long antenna is 'director'
elements, which create a kind of shadow on the active
dipole. The rays get past if you aren't roughly lined up with
the line-of-sight to the transmitter.

Also, such a long antenna has high 'gain' which means it
MUST be aimed carefully; how can you possibly adjust it
if it's bumping into the roof?

I may be confused about what "gain" is. Why would a high gain antenna
have to be aimed carefully? If it has high gain, it seems like it
would have some gain to spare if it were badly aimed.

If it had low gain, it seems like it would have to be aimed precisely.

High gain means "narrow bundle" , so a high gain antenna needs
careful aiming.

So what aobut people on mountains and in valleys, where the
transmitter is lower or higher than they are. Should their antennas
be tipped down or up to aim at the transimitting antenna?

I never hear anyone recommend that, and afaicr (and I don't spend much
time near mountains, but some), every outdoor antenna I've ever seen
has been horizontal.

In any situation, if you have done this before, sometimes
it helps and sometimes it doesn't. You are also likely to see
similar results rotating the antenna from horizontal. The transmitted
waves change the plane as it moves over obsticles, so one station
may work better tilted 10 degrees, but it may make the other station worse.

Gain is made by narrowing the beamwidth and providing more front to back ratio.
A NASA 85 foot dish has about a 1 degree beamwidth at 2.3 gHz.

greg