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Connecting Two Antennas

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Anonymous
July 25, 2004 1:52:31 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

I got the UHF Zenith Directional and it does a beautifull job.

I have another couple stations in a different direction and was wondering if
I could put the same brand on the same pole. Point one in a different
direction and put the 300 ohm wires together and come out of that same
tranformer. If so, about how far apart do you think they should be to be
sinked with each other ?

Oh, and a Samsung 351 OTS Reciever.

More about : connecting antennas

July 25, 2004 3:44:59 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <iYSdnTjQBeH4vZ7cRVn-hQ@giganews.com>,
JoeT@mailpuppy.com says...
> I got the UHF Zenith Directional and it does a beautifull job.
>
> I have another couple stations in a different direction and was wondering if
> I could put the same brand on the same pole. Point one in a different
> direction and put the 300 ohm wires together and come out of that same
> tranformer.

No. After the conversion to 75 Ohm, put a combiner in to
take it back down to one cable for the down-feed.

> If so, about how far apart do you think they should be to be
> sinked with each other ?

Not sure why you're trying to sinc your antennas. It isn't
necessary.

You Should be aware, however, that they Will interact with
each other. The closer they are, the greater the
interaction. This has the potential to create reception
problems for you.
--
Mark

The truth as I perceive it to be.
Your perception may be different.

Triple Z is spam control.
Anonymous
July 25, 2004 8:09:53 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

"Joe H" <JoeT@mailpuppy.com> wrote:

> I got the UHF Zenith Directional and it does a beautifull job.
>
>I have another couple stations in a different direction and was wondering if
>I could put the same brand on the same pole. Point one in a different
>direction and put the 300 ohm wires together and come out of that same
>tranformer. If so, about how far apart do you think they should be to be
>sinked with each other ?
>
The problem with stacking two UHF antennae is that the signals they
receive will be out of phase. If you look at a 2-way or 4-way stacked
antenna you will see that the active elements are tied together with a
carefully measured strip, usually with a twist in the middle. Like
this ===x===

If your two antennae are selective enough that you do not receive the
same station on two of them, you can probably get away with combining
the signals. But you'll have to account for the impedance. You can't
just twist the wires together.

Maybe you could buy a 2-way antennae and twist it so that one element
pointed at each transmitter. (Sounds like a fun project.)

Also, I recommend running the 300-ohm twin line from your UHF antenna
as far as possible (like right up to the set) before converting to
75-ohm coax.
Related resources
Anonymous
July 25, 2004 8:17:48 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

"Joe H" <JoeT@mailpuppy.com> wrote in
news:iYSdnTjQBeH4vZ7cRVn-hQ@giganews.com:

> I got the UHF Zenith Directional and it does a beautifull job.
>
> I have another couple stations in a different direction and was
> wondering if I could put the same brand on the same pole. Point one in
> a different direction and put the 300 ohm wires together and come out
> of that same tranformer. If so, about how far apart do you think they
> should be to be sinked with each other ?
>
> Oh, and a Samsung 351 OTS Reciever.

I don't recommend this. If you MUST use two antennas instead of a
rotator, then use a switch. If the antennas have amplifiers, make sure
that the switch can handle the power voltages without shorting them out.

Even using a combiner as Mark suggests is not recommended, as it will
deteriorate the signals. This may be all right, if the signals are
strong enough to begin with, but the main reason for using directional
antennas is to eliminate reflections and having a second antenna online
and pointed in a different direction is going to pull in any reflections
from that direction.


--
Dave Oldridge+
ICQ 1800667

A false witness is worse than no witness at all.
Anonymous
July 25, 2004 8:41:19 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <Xns9530D8E89267doldridgsprintca@24.71.223.159>,
Dave Oldridge <doldridg@leavethisoutshaw.ca> writes:
> "Joe H" <JoeT@mailpuppy.com> wrote in
> news:iYSdnTjQBeH4vZ7cRVn-hQ@giganews.com:
>
>> I got the UHF Zenith Directional and it does a beautifull job.
>>
>> I have another couple stations in a different direction and was
>> wondering if I could put the same brand on the same pole. Point one in
>> a different direction and put the 300 ohm wires together and come out
>> of that same tranformer. If so, about how far apart do you think they
>> should be to be sinked with each other ?
>>
>> Oh, and a Samsung 351 OTS Reciever.
>
> I don't recommend this. If you MUST use two antennas instead of a
> rotator, then use a switch. If the antennas have amplifiers, make sure
> that the switch can handle the power voltages without shorting them out.
>
I was going to make the same statement, but I'll agree. Mixing two
antennas without very careful design and measurement is likely to
cause problems.

In my own setup, I use two seperate antennas, one for UHF and one for VHF.
However, I use a 'diplexer', which filters the frequency spectrum, and
keeps the VHF antenna from causing too much destructive influence against
the UHF reception. THIS IS DIFFERENT FROM THE ORIGINAL QUESTION, because
the original question was dealing with the same frequency band, however.

John
Anonymous
July 25, 2004 8:41:20 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <cdvdlf$28a$2@news.iquest.net>, toor@iquest.net says...
> In my own setup, I use two seperate antennas, one for UHF and one for VHF.
> However, I use a 'diplexer', which filters the frequency spectrum, and
> keeps the VHF antenna from causing too much destructive influence against
> the UHF reception. THIS IS DIFFERENT FROM THE ORIGINAL QUESTION, because
> the original question was dealing with the same frequency band, however.

There are combiners (aka diplexers)available which will conbine two
antennas for the same band without interference. If you want to
combine different lo-vhf (2-6), high vhf (7-13), and uhf (14+), that
is easy. If you need two antennas on say lo-vhf, that is a little
more difficult (needs better filters). Do a Google for CATV
(community antenna) products. You won't find these products at Radio
Shack.

Here is a general reference on stacking and combining antennas
http://www.kyes.com/antenna/stacking.html
that may get you started


/Chris, AA6SQ
July 25, 2004 8:44:34 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

"John S. Dyson" <toor@iquest.net> wrote in message
news:cdvdlf$28a$2@news.iquest.net...
> In article <Xns9530D8E89267doldridgsprintca@24.71.223.159>,
> Dave Oldridge <doldridg@leavethisoutshaw.ca> writes:
> > "Joe H" <JoeT@mailpuppy.com> wrote in
> > news:iYSdnTjQBeH4vZ7cRVn-hQ@giganews.com:
> >
> >> I got the UHF Zenith Directional and it does a beautifull job.
> >>
> >> I have another couple stations in a different direction and was
> >> wondering if I could put the same brand on the same pole. Point one in
> >> a different direction and put the 300 ohm wires together and come out
> >> of that same tranformer. If so, about how far apart do you think they
> >> should be to be sinked with each other ?
> >>
> >> Oh, and a Samsung 351 OTS Reciever.
> >
> > I don't recommend this. If you MUST use two antennas instead of a
> > rotator, then use a switch. If the antennas have amplifiers, make sure
> > that the switch can handle the power voltages without shorting them out.
> >
> I was going to make the same statement, but I'll agree. Mixing two
> antennas without very careful design and measurement is likely to
> cause problems.
>
> In my own setup, I use two seperate antennas, one for UHF and one for VHF.
> However, I use a 'diplexer', which filters the frequency spectrum, and
> keeps the VHF antenna from causing too much destructive influence against
> the UHF reception. THIS IS DIFFERENT FROM THE ORIGINAL QUESTION, because
> the original question was dealing with the same frequency band, however.
>
> John

That's not a diplexer but probably a UHF/VHF splitter/combiner such as
http://www.radioshack.com/product.asp?catalog%5Fname=CT...

A diplexer combines or separates a satellite signal and an antenna or
cableTV signal.

Pat
Anonymous
July 25, 2004 10:49:31 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <SUGMc.42440$eH1.19852568@newssvr28.news.prodigy.com>,
"Greywolf" <greywolfin45@*spamisbad*sbcglobal.net> writes:
> "John S. Dyson" <toor@iquest.net> wrote in message
> news:cdvdlf$28a$2@news.iquest.net...
>> In article <Xns9530D8E89267doldridgsprintca@24.71.223.159>,
>> Dave Oldridge <doldridg@leavethisoutshaw.ca> writes:
>> > "Joe H" <JoeT@mailpuppy.com> wrote in
>> > news:iYSdnTjQBeH4vZ7cRVn-hQ@giganews.com:
>> >
>> >> I got the UHF Zenith Directional and it does a beautifull job.
>> >>
>> >> I have another couple stations in a different direction and was
>> >> wondering if I could put the same brand on the same pole. Point one in
>> >> a different direction and put the 300 ohm wires together and come out
>> >> of that same tranformer. If so, about how far apart do you think they
>> >> should be to be sinked with each other ?
>> >>
>> >> Oh, and a Samsung 351 OTS Reciever.
>> >
>> > I don't recommend this. If you MUST use two antennas instead of a
>> > rotator, then use a switch. If the antennas have amplifiers, make sure
>> > that the switch can handle the power voltages without shorting them out.
>> >
>> I was going to make the same statement, but I'll agree. Mixing two
>> antennas without very careful design and measurement is likely to
>> cause problems.
>>
>> In my own setup, I use two seperate antennas, one for UHF and one for VHF.
>> However, I use a 'diplexer', which filters the frequency spectrum, and
>> keeps the VHF antenna from causing too much destructive influence against
>> the UHF reception. THIS IS DIFFERENT FROM THE ORIGINAL QUESTION, because
>> the original question was dealing with the same frequency band, however.
>>
>> John
>
> That's not a diplexer but probably a UHF/VHF splitter/combiner such as
> http://www.radioshack.com/product.asp?catalog%5Fname=CT...
>
> A diplexer combines or separates a satellite signal and an antenna or
> cableTV signal.
>
The term 'diplexer' is a more general technical term than that. Such
devices are used in the seperation of spectrum -- sometimes to/from the
same load. (e.g. a diplexer is also used after a balanced diode mixer
to effect a flat load to the mixers, where part of the spectrum is
passed on to the IF, and the other part is passed on to a dummy load.)

There is no requirement that a diplexer have anything to do with a satellite
signal. The notion of a 'diplexer' seems more often to be used for
frequency seperation/combining...

John
Anonymous
July 25, 2004 10:57:52 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <MPG.1b6ce6d5aaaf1b81989848@news.mminternet.com>,
Chris Thomas <cthomas@mminternet.com> writes:
> In article <cdvdlf$28a$2@news.iquest.net>, toor@iquest.net says...
>> In my own setup, I use two seperate antennas, one for UHF and one for VHF.
>> However, I use a 'diplexer', which filters the frequency spectrum, and
>> keeps the VHF antenna from causing too much destructive influence against
>> the UHF reception. THIS IS DIFFERENT FROM THE ORIGINAL QUESTION, because
>> the original question was dealing with the same frequency band, however.
>
> There are combiners (aka diplexers)available which will conbine two
> antennas for the same band without interference. If you want to
> combine different lo-vhf (2-6), high vhf (7-13), and uhf (14+), that
> is easy.
>
I was simply explaining the possibility of easily using multiple
antennas, but it is easy if you use a diplexer and are using
the antennas to receive different bands. (Well, you might not need
a diplexer if the antennas won't mutually interfere, but that is
more likely than not to happen.) There are NUMEROUS applications
in the HDTV world where there are both VHF and UHF HDTV channels,
and combining the signal from two antennas is a potentially common
requirement. It isn't sufficient to simply add the two antennas together
when you might use a dipole and UHF antenna, where the dipole will work
somewhat at UHF (possibly with lots of gain, but also receiving lots of
reflections due to wierd reception pattern.)

Definition of diplexer:
diplexer: A three-port frequency-dependent device that may be
used as a separator or a combiner of signals. Note: Duplex
transmission through a diplexer is not possible.

Note that other comments from other postings that imply something
to do with 'satellites' isn't operative. The only reason why
you'd use it with satellites is for the express purpose of splitting
or combining the signals from different frequency ranges (which is
what is desired in that specific application.)

>
> You won't find these products at Radio
> Shack.
>
Please refer to Radio Shack #15-1236. It certainly does appear
to be frequency selective, and meet the definition of diplexer.
They might not call it a diplexer, but that might be because the
populace doesn't really know what a diplexer is :-).

John
Anonymous
July 25, 2004 12:47:17 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

Of the several 'near-on' replies to this question/thread, Mr. Gordon is
the one who came the closest to hitting the nail on the head.

Obviously with a commercially-made multi-stack array you most certainly
CAN use multiple antennas (within the same frequency band) to augment the
gain while at the same time significantly improving the front-to-side and
front-to-back ratios (directivity). This also has the net effect of
sharpening the main lobe (narrowing the beamwidth) which is normally
desirable. Such an array can be called for in deep fringe areas and in
fact will normally provide better performance than just a single antenna
with a preamp. The multi-stack array captures more signal out of the air
whereas the preamplifier only amplifies what it sees. It's the old GIGO
theory (Garbage In = Garbage Out). The preamp is of course much cheaper
and easier.

Feedline loss is also a major factor at UHF frequencies so I was glad to
see Mr. Gordon's intelligent recommendation to use 300-ohm twinlead and
place the BALUN as close to the receiver as possible. Unfortunately, he
only went half-way and did not explain the proper method of installing
300-ohm twinlead using standoffs and a gentle twist of approx. 1 turn per
foot. Alas, I know he meant well ;) 

The "carefully measured strip" connecting the antennas in a multi-stack
array together is what's called a co-phasing harness. Physical length as
well as line impedance of each portion of this device is extremely
critical. The object is to bring the signals captured by each antenna
together IN PHASE with one another so that they are additive and combine
to produce a stronger signal. By the same token, to provide maximum signal
transfer it is important that the co-phasing harness act also as an
impedance matching device. All of this amounts to some fairly high level
and scientific antenna theory which can be proven both in complex
mathmatical formulas and seen in practical application with the aid of
oscilloscopes and sensitive metering devices.

GREEK TO MOST OF US, but the bottom line is that you cannot arbitrarily
connect two or more (same frequency band) antennas together and achieve
the maximum desired effect without knowing what you're doing and doing it
correctly from the scientific standpoint (anecdotal amateur testimonials
notwithstanding).

In "Joe's" situation trying to address signals in opposing directions, the
best recommendation for doing it the right way would probably be to use 1
antenna with a rotator or use 2 separate antennas with individual 300-ohm
downleads (separated w/dual standoffs, not taped together) and a 300-ohm
A/B switch ahead of the BALUN. Avoid use of a preamp unless absolutely
necessary.

In article <r4q6g0lgnagdtipagl8bvucktfo7257lsk@4ax.com> Guy Gordon
<gordon@NOSPAMwhite-crane.com> writes:

>"Joe H" <JoeT@mailpuppy.com> wrote:

>> I got the UHF Zenith Directional and it does a beautifull job.

>>I have another couple stations in a different direction and was wondering if
>>I could put the same brand on the same pole. Point one in a different
>>direction and put the 300 ohm wires together and come out of that same
>>tranformer. If so, about how far apart do you think they should be to be
>>sinked with each other ?

>The problem with stacking two UHF antennae is that the signals they
>receive will be out of phase. If you look at a 2-way or 4-way stacked
>antenna you will see that the active elements are tied together with a
>carefully measured strip, usually with a twist in the middle. Like
>this ===x===

>If your two antennae are selective enough that you do not receive the
>same station on two of them, you can probably get away with combining
>the signals. But you'll have to account for the impedance. You can't
>just twist the wires together.

>Maybe you could buy a 2-way antennae and twist it so that one element
>pointed at each transmitter. (Sounds like a fun project.)

>Also, I recommend running the 300-ohm twin line from your UHF antenna
>as far as possible (like right up to the set) before converting to
>75-ohm coax.


--
Help Support Satellite Radio!
Your local radio broadcasters through their powerful NAB lobbyiests
are currently pushing a bill through Congress that if passed, would block
the Satellite Radio services from carrying local content (Traffic & Weather)
Please call your elected representatives at (202) 225-3121 and urge them to
Oppose HR 4026. We need your help, please.
<http://www.xmradio.com/grassroots/index.jsp&gt;
Anonymous
July 25, 2004 9:29:49 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <2ab7g019hkf7vs4397td47q93ssks127k8@4ax.com>,
MrFixit@msn.com (Mr Fixit) writes:
>
> Feedline loss is also a major factor at UHF frequencies so I was glad to
> see Mr. Gordon's intelligent recommendation to use 300-ohm twinlead and
> place the BALUN as close to the receiver as possible. Unfortunately, he
> only went half-way and did not explain the proper method of installing
> 300-ohm twinlead using standoffs and a gentle twist of approx. 1 turn per
> foot. Alas, I know he meant well ;) 
>
Twinlead is often a short term advantage only. Even 'proper installation'
of twinlead will often present a longer term degradation. The better
choice (assuming proper layout) is to use a properly designed preamp
immediately at the antenna, then use coax. Preamps today are different
in capability than preamps 10-20yrs ago (or worse, longer back.) It
is important to avoid getting a cheap one.

As a lab exercise, twinlead is certainly less lossy than coax, but it
is also more prone to aging effects. (Part of the advantage of low
loss twinlead is to take partial advantage of the relatively lossless air
dielectric. This helps to intuitively show the low shielding level
with twinlead (it depends upon the air around the twinlead.) The
'air' around the twinlead can easily become corrupt.


> The "carefully measured strip" connecting the antennas in a multi-stack
> array together is what's called a co-phasing harness. Physical length as
> well as line impedance of each portion of this device is extremely
> critical. The object is to bring the signals captured by each antenna
> together IN PHASE with one another so that they are additive and combine
> to produce a stronger signal.
>
Actually, your earlier comment is more technically accurate than your
implication of 'in-phase' reception here. In essense, given a relatively
lossless environment, the pattern of the antenna will change, depending
upon the relative positions of the constituents. The ability to receive
in any given direction will be optimized based upon the element
configuration. For a non-techie (and many techies), it is also important
to avoid getting caught up in 'antenna gain' relative to frequency
issues. At higher frequencies, for example, the gain of a given configuration
is given relative to a specific antenna. That antenna becomes smaller as
the frequency increases, and therefore a 'high gain' antenna at higher
frequencies might capture less signal than a low gain antenna at lower
frequencies. (This is PART of the reason why UHF transmitters do run
with higher ERP -- because the smaller UHF antennas at homes tend to
capture less signal. For example, a 0dB gain antenna at 50MHz will be
more equivalent to a 3dB gain at 100MHz than a 0dB gain at 100MHz...

The problem with UHF antennas is to create a configuration with a defined
directivity, yet capture more signal. A small dipole that is optimized
for UHF will capture relatively less of the UHF signal than the same
dipole that is optimized for VHF will capture for VHF.

>
> By the same token, to provide maximum signal
> transfer it is important that the co-phasing harness act also as an
> impedance matching device. All of this amounts to some fairly high level
> and scientific antenna theory which can be proven both in complex
> mathmatical formulas and seen in practical application with the aid of
> oscilloscopes and sensitive metering devices.
>
Actually, the technology needed to properly configure an antenna isn't
too bad, but most people (including engineers) don't have the experience
to do so. For a little fun, some simulations with the NEC series of
programs will help to show the needed precision and the degrees of
freedom that can be daunting. The degrees of freedom in antenna design
(various configurations in three dimensions) helps to show the antenna
ignorant person that it isn't easy without a deep understanding. Using
'tools' is of limited value without a deep understanding.

>
> GREEK TO MOST OF US, but the bottom line is that you cannot arbitrarily
> connect two or more (same frequency band) antennas together and achieve
> the maximum desired effect without knowing what you're doing and doing it
> correctly from the scientific standpoint (anecdotal amateur testimonials
> notwithstanding).
>
As I had suggested before, trying one of the NEC programs (hopefully
with a GUI) would be instructive.

>
> In "Joe's" situation trying to address signals in opposing directions, the
> best recommendation for doing it the right way would probably be to use 1
> antenna with a rotator or use 2 separate antennas with individual 300-ohm
> downleads (separated w/dual standoffs, not taped together) and a 300-ohm
> A/B switch ahead of the BALUN. Avoid use of a preamp unless absolutely
> necessary.
>
Unless in a controlled environment, I strongly suggest using coax. Twinlead
is often a false advantage over time. The loss per foot is only one parameter
of a full engineering choice.

When talking about all of this, trying for an 'optimal' minimal loss design,
as soon as a 5-7dB NF front end is encounted, then any illusion of
being 'optimum' becomes null and void. With todays technology, it is
very reasonable to provide a <1dB NF at an antenna with a preamp that
would almost NEVER overload. (A tuned front end of a TV would overload before
the preamp.)

It is important to do a loss budget, and also DESIGN the configuration.
I wouldn't wish generic 'twin lead' (even properly laid out and with
proper standoffs) on anyone, except someone who likes to tweak their
system.

John
Anonymous
July 25, 2004 10:49:51 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

MR Fixit, and John, you too are very interesting people.

Reason: When I was young I took up a electronics course for two years then
moved to where I live now and ended up doing a common job in a factory for
10 years, then to maintainance for 10 years, then downsizing, doing almost
anything till I got disabled another 10 years later.

I was very interested in working with CB Radio's and knew a guy who had a
directional CB antenna on a 100 foot tower and we were going to put another
one under it, that's where one of you rang a bell with Phasing, but in only
the same direction. I don't know what you know, but know about a twist in a
300 ohm wire to 'Throw off Static as we called it by then'. It was very good
reading and your both good at what you say, know, and do, and I thank you
very much.
You guys could write a good book if you got together that I would read.

Ok, now that said, I'm going to post a New post about a better antenna then
I have, see ' my post Sun 25th.

"John S. Dyson" <toor@iquest.net> wrote in message
news:ce0qmc$f7c$1@news.iquest.net...
> In article <2ab7g019hkf7vs4397td47q93ssks127k8@4ax.com>,
> MrFixit@msn.com (Mr Fixit) writes:
> >
> > Feedline loss is also a major factor at UHF frequencies so I was glad to
> > see Mr. Gordon's intelligent recommendation to use 300-ohm twinlead and
> > place the BALUN as close to the receiver as possible. Unfortunately, he
> > only went half-way and did not explain the proper method of installing
> > 300-ohm twinlead using standoffs and a gentle twist of approx. 1 turn
per
> > foot. Alas, I know he meant well ;) 
> >
> Twinlead is often a short term advantage only. Even 'proper installation'
> of twinlead will often present a longer term degradation. The better
> choice (assuming proper layout) is to use a properly designed preamp
> immediately at the antenna, then use coax. Preamps today are different
> in capability than preamps 10-20yrs ago (or worse, longer back.) It
> is important to avoid getting a cheap one.
>
> As a lab exercise, twinlead is certainly less lossy than coax, but it
> is also more prone to aging effects. (Part of the advantage of low
> loss twinlead is to take partial advantage of the relatively lossless air
> dielectric. This helps to intuitively show the low shielding level
> with twinlead (it depends upon the air around the twinlead.) The
> 'air' around the twinlead can easily become corrupt.
>
>
> > The "carefully measured strip" connecting the antennas in a multi-stack
> > array together is what's called a co-phasing harness. Physical length as
> > well as line impedance of each portion of this device is extremely
> > critical. The object is to bring the signals captured by each antenna
> > together IN PHASE with one another so that they are additive and combine
> > to produce a stronger signal.
> >
> Actually, your earlier comment is more technically accurate than your
> implication of 'in-phase' reception here. In essense, given a relatively
> lossless environment, the pattern of the antenna will change, depending
> upon the relative positions of the constituents. The ability to receive
> in any given direction will be optimized based upon the element
> configuration. For a non-techie (and many techies), it is also important
> to avoid getting caught up in 'antenna gain' relative to frequency
> issues. At higher frequencies, for example, the gain of a given
configuration
> is given relative to a specific antenna. That antenna becomes smaller as
> the frequency increases, and therefore a 'high gain' antenna at higher
> frequencies might capture less signal than a low gain antenna at lower
> frequencies. (This is PART of the reason why UHF transmitters do run
> with higher ERP -- because the smaller UHF antennas at homes tend to
> capture less signal. For example, a 0dB gain antenna at 50MHz will be
> more equivalent to a 3dB gain at 100MHz than a 0dB gain at 100MHz...
>
> The problem with UHF antennas is to create a configuration with a defined
> directivity, yet capture more signal. A small dipole that is optimized
> for UHF will capture relatively less of the UHF signal than the same
> dipole that is optimized for VHF will capture for VHF.
>
> >
> > By the same token, to provide maximum signal
> > transfer it is important that the co-phasing harness act also as an
> > impedance matching device. All of this amounts to some fairly high level
> > and scientific antenna theory which can be proven both in complex
> > mathmatical formulas and seen in practical application with the aid of
> > oscilloscopes and sensitive metering devices.
> >
> Actually, the technology needed to properly configure an antenna isn't
> too bad, but most people (including engineers) don't have the experience
> to do so. For a little fun, some simulations with the NEC series of
> programs will help to show the needed precision and the degrees of
> freedom that can be daunting. The degrees of freedom in antenna design
> (various configurations in three dimensions) helps to show the antenna
> ignorant person that it isn't easy without a deep understanding. Using
> 'tools' is of limited value without a deep understanding.
>
> >
> > GREEK TO MOST OF US, but the bottom line is that you cannot arbitrarily
> > connect two or more (same frequency band) antennas together and achieve
> > the maximum desired effect without knowing what you're doing and doing
it
> > correctly from the scientific standpoint (anecdotal amateur testimonials
> > notwithstanding).
> >
> As I had suggested before, trying one of the NEC programs (hopefully
> with a GUI) would be instructive.
>
> >
> > In "Joe's" situation trying to address signals in opposing directions,
the
> > best recommendation for doing it the right way would probably be to use
1
> > antenna with a rotator or use 2 separate antennas with individual
300-ohm
> > downleads (separated w/dual standoffs, not taped together) and a 300-ohm
> > A/B switch ahead of the BALUN. Avoid use of a preamp unless absolutely
> > necessary.
> >
> Unless in a controlled environment, I strongly suggest using coax.
Twinlead
> is often a false advantage over time. The loss per foot is only one
parameter
> of a full engineering choice.
>
> When talking about all of this, trying for an 'optimal' minimal loss
design,
> as soon as a 5-7dB NF front end is encounted, then any illusion of
> being 'optimum' becomes null and void. With todays technology, it is
> very reasonable to provide a <1dB NF at an antenna with a preamp that
> would almost NEVER overload. (A tuned front end of a TV would overload
before
> the preamp.)
>
> It is important to do a loss budget, and also DESIGN the configuration.
> I wouldn't wish generic 'twin lead' (even properly laid out and with
> proper standoffs) on anyone, except someone who likes to tweak their
> system.
>
> John
>
Anonymous
July 26, 2004 12:26:30 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

Chris Thomas <cthomas@mminternet.com> wrote in
news:MPG.1b6ce6d5aaaf1b81989848@news.mminternet.com:

> In article <cdvdlf$28a$2@news.iquest.net>, toor@iquest.net says...
>> In my own setup, I use two seperate antennas, one for UHF and one for
>> VHF. However, I use a 'diplexer', which filters the frequency
>> spectrum, and keeps the VHF antenna from causing too much destructive
>> influence against the UHF reception. THIS IS DIFFERENT FROM THE
>> ORIGINAL QUESTION, because the original question was dealing with the
>> same frequency band, however.
>
> There are combiners (aka diplexers)available which will conbine two
> antennas for the same band without interference. If you want to

And this is fine if the two antennas are not picking up signals that will
interact AFTER they are recombined. As I said, a switch is the best
answer to this problem. Combining two antennas for DIFFERENT frequencies
is not a huge technical problem, but whenever you combine two antennas on
the same channel, you either need VERY decent signals from two different
sources or a path with no reflections from the primary source. Even
then, there are whole issues of placement involved. Any time that
signals from two antennas, derived from a single source, are involved,
there are phasing issues and that means tha a displacement of a few
inches can make a large difference in the combined signal's
presentability. This is even MORE true with digital signals than with
analog and more difficult to detect and rectify, since it must be done on
frequency and you cannot SEE the phasing with a digital signal!

> combine different lo-vhf (2-6), high vhf (7-13), and uhf (14+), that
> is easy. If you need two antennas on say lo-vhf, that is a little
> more difficult (needs better filters). Do a Google for CATV
> (community antenna) products. You won't find these products at Radio
> Shack.

CATV combiners are usually all about combining signals on DIFFERENT
frequencies onto the same broadband feed.

> Here is a general reference on stacking and combining antennas
> http://www.kyes.com/antenna/stacking.html
> that may get you started

This is pretty good. But my antenna guru is John Kraus, W8JK (who wrote
the book on them). He died recently but his book lives on.

> /Chris, AA6SQ


--
Dave Oldridge+
ICQ 1800667
VA7CZ

A false witness is worse than no witness at all.
Anonymous
July 26, 2004 12:26:31 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <Xns953189016FC91doldridgsprintca@24.71.223.159>,
doldridg@leavethisoutshaw.ca says...
>
> And this is fine if the two antennas are not picking up signals that will
> interact AFTER they are recombined. As I said, a switch is the best
> answer to this problem.

A switch is about the only solution if you want two stations on the
same channel in different directions. Stacking antennas for either
increased gain or increased directivity on a single station (eg, to
eliminate a pesky reflection) is certainly possible, but really is
only feasible with single channel antennas (else, how would one phase
them). I've seen fancy CATV installations that did this, but not
usually a single homeowner. I once worked on a mountaintop CATV setup
that had 2x2 stacks of single channel ants for each of six channels;
that's 24 yagis! (One sees two ch 2-13 antennas stacked on homes, but
I have yet to be convinced the result was superior to a single ant.)

> This is pretty good. But my antenna guru is John Kraus, W8JK (who wrote
> the book on them).

Dave, I'd never argue with Kraus. But his work is a little deep for
the average layman ... ;-) I was looking for something the OP could
get into.

/Chris, AA6SQ
Anonymous
July 26, 2004 9:39:43 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

Joe H wrote:
> I got the UHF Zenith Directional and it does a beautifull job.
>
> I have another couple stations in a different direction and was wondering if
> I could put the same brand on the same pole. Point one in a different
> direction and put the 300 ohm wires together and come out of that same
> tranformer. If so, about how far apart do you think they should be to be
> sinked with each other ?
>
> Oh, and a Samsung 351 OTS Reciever.
>
>

Reception from two different directions can be a challenge. I live
between two cities (call then A at 17 miles and B at 30 miles for
simplicity) which are 150 degrees apart. Even though the terrain is
super flat, the antenna pointed toward city A will also receive ghosting
from the transmitters in city B, and likewise the antenna pointed toward
city B will receive ghosting from city A. Not only does ghosting
increase but also noise. Channel 22 from city B will also pick up the
noise on channel 22 from antenna A. Analog pictures with this kind of
dual antenna system contain significant ghosting and look noisy. In
comparison, a single antenna oriented with a rotor gets perfect analog
and digital reception from both cities.
The dual combined antenna system may not be acceptable for analog
reception, but may work fine for digital tv and might be worth a try. If
not then an A/B switch, as previously mentioned, may be your best choice
for fast selection between cities. A rotor is also a good choice but in
my case is far too slow to turn 150 degrees. Obviously, either the rotor
or A/B switch will work for a single tv, but not for multiple tv sets
which are tuned to different cities.
Anonymous
July 26, 2004 12:19:00 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

I think one of the root problems identified here is we have spawned a
generation of couch potatoes that has been collectively spoiled by the
convenience of the armchair remote control and the onscreen guide.

An antenna rotator that takes 30-40 seconds or flipping an A/B switch are
both relics of the 1950s, literally museum pieces, and means we have to
drag our lazy asses up off the couch to change the channel. This tears at
the very fabric of "channel surfing".

The workaround for the epitome of laziness (with an unlimited budget) is
to install individual, 18-element Decibel Products corner reflectors, each
one cut exactly for the precise desired frequency and precisely aimed. In
turn, connect each of these to individual, sharply tuned, Blonder-Tongue
single channel AGC controlled strip amplifiers and feed the outputs of
each of those into a multi-port combiner. Install pads at the combiner
inputs as necessary to achieve signal level flatness across the desired
baseband.

Finally, purchase and install a quality grade of PVR with a lifetime
subscription. (This solves the onscreen guide problem).

Now sit back, relax and watch TV.

In article <zO0Nc.136687$OB3.128003@bgtnsc05-news.ops.worldnet.att.net>
numeric <numeric@att.net> writes:



>Joe H wrote:
>> I got the UHF Zenith Directional and it does a beautifull job.

>> I have another couple stations in a different direction and was wondering if
>> I could put the same brand on the same pole. Point one in a different
>> direction and put the 300 ohm wires together and come out of that same
>> tranformer. If so, about how far apart do you think they should be to be
>> sinked with each other ?

>> Oh, and a Samsung 351 OTS Reciever.

>Reception from two different directions can be a challenge. I live
>between two cities (call then A at 17 miles and B at 30 miles for
>simplicity) which are 150 degrees apart. Even though the terrain is
>super flat, the antenna pointed toward city A will also receive ghosting
>from the transmitters in city B, and likewise the antenna pointed toward
>city B will receive ghosting from city A. Not only does ghosting
>increase but also noise. Channel 22 from city B will also pick up the
>noise on channel 22 from antenna A. Analog pictures with this kind of
>dual antenna system contain significant ghosting and look noisy. In
>comparison, a single antenna oriented with a rotor gets perfect analog
>and digital reception from both cities.
>The dual combined antenna system may not be acceptable for analog
>reception, but may work fine for digital tv and might be worth a try. If
>not then an A/B switch, as previously mentioned, may be your best choice
>for fast selection between cities. A rotor is also a good choice but in
>my case is far too slow to turn 150 degrees. Obviously, either the rotor
>or A/B switch will work for a single tv, but not for multiple tv sets
>which are tuned to different cities.

--
If common sense and brains were gasoline, there are some who haven't enough
to run a piss ant's motorcycle 1 revolution around the inside of a Cheerio.
Anonymous
July 26, 2004 12:21:14 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

Chris Thomas <cthomas@mminternet.com> wrote in
news:MPG.1b6dfab4a3ad702a989849@news.mminternet.com:

> In article <Xns953189016FC91doldridgsprintca@24.71.223.159>,
> doldridg@leavethisoutshaw.ca says...
>>
>> And this is fine if the two antennas are not picking up signals that
>> will interact AFTER they are recombined. As I said, a switch is the
>> best answer to this problem.
>
> A switch is about the only solution if you want two stations on the
> same channel in different directions. Stacking antennas for either
> increased gain or increased directivity on a single station (eg, to
> eliminate a pesky reflection) is certainly possible, but really is
> only feasible with single channel antennas (else, how would one phase
> them). I've seen fancy CATV installations that did this, but not
> usually a single homeowner. I once worked on a mountaintop CATV setup
> that had 2x2 stacks of single channel ants for each of six channels;
> that's 24 yagis! (One sees two ch 2-13 antennas stacked on homes, but
> I have yet to be convinced the result was superior to a single ant.)

True....years ago here in the Vancouver area you used to see two channel
12 heads stacked, which made perfect sense, since you can SEE the
transmitter from any part of Vancouver's south slope. But front ends got
better and cable came along. You can get 12 on rabbit ears most parts of
Vancouver now (though it's dicey here in Chilliwack).

>> This is pretty good. But my antenna guru is John Kraus, W8JK (who
>> wrote the book on them).

> Dave, I'd never argue with Kraus. But his work is a little deep for
> the average layman ... ;-) I was looking for something the OP could
> get into.
>
> /Chris, AA6SQ

Unfortunately, John's obituary was in a recent QST, but his engineering
textbook on antennas is still my bible on the subject. That and some
decent software!

My exploits consist of putting together a rather loud 2 meter system on
the east coast (Halifax area) that could hear Boston on CW and SSB
(though not always be heard by the deaf guys down there), and a 2-element
steerable pair of verticals for 80-40-20 meters (mainly used on 80 and
40).

--
Dave Oldridge+
ICQ 1800667

A false witness is worse than no witness at all.
Anonymous
July 26, 2004 12:35:19 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <Xns9532E0BBD325doldridgsprintca@24.71.223.159> Dave Oldridge
<doldridg@leavethisoutshaw.ca> writes:


>My exploits consist of putting together a rather loud 2 meter system on
>the east coast (Halifax area) that could hear Boston on CW and SSB
>(though not always be heard by the deaf guys down there), and a 2-element
>steerable pair of verticals for 80-40-20 meters (mainly used on 80 and
>40).

You guys and your verticals, I swear. My goal for the ultimate in
directional arrays for 160-80-40-20 is to build the shack dead-center in
the middle of an 80-acre field. Then with the aid of a massive collection
of old Rohn-6 and Rohn-25 TV towers, erect 12 long-wire "V-beams", 1000'
on a leg, every 30 degrees. Light it up with a Henry 2K Ultra. You will be
heard!


---
There's a red carnation on the can
cause it's the best milk in the land.
No tits to twitch, no chips to pitch,
just punch two holes in the sonuvabitch.
!