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Posted by Tony Hwang on May 2, 2009, 10:32 pm
tnom@mucks.net wrote:
> wrote:
>
>> tnom@mucks.net wrote:
>>>> Hi,
>>>> Yeah! And add to it, height matters too. The higher the better is not
>>>> really the case. You gotta hit the sweet spot height wise.
>>> Huh? Height gain is real and exist for all frequencies. The only
>>> time excess height will work against you is when your feed line losses
>>> outweigh you height gain. You'll have to go very high for this to
>>> happen on TV frequencies. There is no sweet spot unless you
>>> are somehow physically obstructed.
>> Hmm,
>> From the days when I was active in telecommunications engineering,
>> I was trying to capture long distance TV relay signal, guess what?
>> I could only get a decent stable signal at certain height on the tower.
>> Lower or higher the signal disappeared. Had numerous instances like this
>> on VHF, UHF, troposcatter, microwave repeater installations. Retired in
>> '96 after spending my whole life in the field and been a ham since my
>> boyhood as well.
>> Class of '60, EE.
>> VE6CGX
>
> Then you must be misinterpreting what is going on. Height is never
> detrimental to an antenna unless line losses come into play.
Hi,
Line loss on what? Hard coax, nitrogen charged waveguide have very low
loss and SWR is near 1 to 1. Explain then why signal disappears when
height is lowered.
Noise level is more important than signal level when dealing with
terrestrial signal.(-90db range)
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Posted by on May 2, 2009, 11:03 pm
>> Then you must be misinterpreting what is going on. Height is never
>> detrimental to an antenna unless line losses come into play.
>Hi,
>Line loss on what? Hard coax, nitrogen charged waveguide have very low
>loss and SWR is near 1 to 1.
Standard TV coax is on subject. It does have losses that should be
considered.
>Explain then why signal disappears when
>height is lowered.
In theory (doesn't exist in this case) e fields can cancel or be
additive at different heights.
>Noise level is more important than signal level when dealing with
>terrestrial signal.(-90db range)
Maybe you forgot that the subject is a TV antenna. No nitrogen
charged wave guide. No hard coax. This is a TV antenna. A TV
antenna is a multiple frequency antenna unlike the ones you seem to
be referring to. A TV antenna does not have radial ground wires buried
in the ground like broadcast antennas to enhance signal gain.
No sweet spot exist for multiple frequency antennas like TV
antennas over normal ground. A TV antenna can not take advantage
of ground reflections because there are no buried radials, and even if
it had buried radials how can you find a sweet spot for the entire
frequency range of the antenna? Raise and lower it when
you change channels?
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Posted by Tony Hwang on May 2, 2009, 11:59 pm
tnom@mucks.net wrote:
>>> Then you must be misinterpreting what is going on. Height is never
>>> detrimental to an antenna unless line losses come into play.
>> Hi,
>> Line loss on what? Hard coax, nitrogen charged waveguide have very low
>> loss and SWR is near 1 to 1.
>
> Standard TV coax is on subject. It does have losses that should be
> considered.
>
>> Explain then why signal disappears when
>> height is lowered.
>
> In theory (doesn't exist in this case) e fields can cancel or be
> additive at different heights.
>
>> Noise level is more important than signal level when dealing with
>> terrestrial signal.(-90db range)
>
> Maybe you forgot that the subject is a TV antenna. No nitrogen
> charged wave guide. No hard coax. This is a TV antenna. A TV
> antenna is a multiple frequency antenna unlike the ones you seem to
> be referring to. A TV antenna does not have radial ground wires buried
> in the ground like broadcast antennas to enhance signal gain.
>
> No sweet spot exist for multiple frequency antennas like TV
> antennas over normal ground. A TV antenna can not take advantage
> of ground reflections because there are no buried radials, and even if
> it had buried radials how can you find a sweet spot for the entire
> frequency range of the antenna? Raise and lower it when
> you change channels?
Hi,
One more and I am out. Is there a theory for TV antenna and another for
microwave? On theory we use isopole or dipole in free space usinf
reference dbi or dbd.
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Posted by on May 3, 2009, 8:22 am
wrote:
>tnom@mucks.net wrote:
>>>> Then you must be misinterpreting what is going on. Height is never
>>>> detrimental to an antenna unless line losses come into play.
>>> Hi,
>>> Line loss on what? Hard coax, nitrogen charged waveguide have very low
>>> loss and SWR is near 1 to 1.
>>
>> No sweet spot exist for multiple frequency antennas like TV
>> antennas over normal ground. A TV antenna can not take advantage
>> of ground reflections because there are no buried radials, and even if
>> it had buried radials how can you find a sweet spot for the entire
>> frequency range of the antenna? Raise and lower it when
>> you change channels?
>Hi,
>One more and I am out. Is there a theory for TV antenna and another for
>microwave? On theory we use isopole or dipole in free space usinf
>reference dbi or dbd.
Theory and reality are very different. In reality microwaves compared
to vhf/uhf waves behave differently when hitting earth ground.
In reality microwaves react differently when it comes to traveling
around the curvature of the earth. In reality microwaves dissipate
differently in air. In reality microwaves use different feed lines. In
reality microwaves are a single frequency. In reality attributing
theory or microwaves to explain a TV antennas behavior is not reality.
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Posted by bob haller on May 2, 2009, 1:54 pm
On May 2, 12:46=EF=BF=BDpm, t...@mucks.net wrote:
> >Hi,
> >Yeah! And add to it, height matters too. The higher the better is not
> >really the case. You gotta hit the sweet spot height wise.
> Huh? Height gain is real and exist for all frequencies. The only
> time excess height will work against you is when your feed line losses
> outweigh you height gain. You'll =EF=BF=BDhave to go very high for this t=
o
> happen on TV frequencies. There is no sweet spot unless you
> are somehow physically obstructed.
not necessarily true. radio waves (tv waves) are like waves on a pond,
in places they add to make larger waves......... in other places they
cancel one another.
So you can go higher and get worse results
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