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Antenna Questions
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apollo
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Joined: 20 Jun 2004
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Post Antenna Questions Reply with quote
Do the following questions apply to LPFM or are they not applicable?

Is the antenna cable length a factor in antenna performance? I heard one time that ideally the length of the antenna cable should be in even wavelengths of the actual transmitter frequency.

Which antenna provides the best performance for a non-directional application under 100w ERP? Considering, a 5/8 wave vs a single or dual dipole type.

It seems that most antennas listed here are vertically polarized; does that affect the ability of home receiver’s vs car radios?

Thanks for your feedback…
Sun Jun 20, 2004 9:22 pm View user's profile Send private message
Black_Hawk
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Post SUBJECTIVE INSINUATIONS Reply with quote
Greetings All,
Nice try..however do a caparison check for your self..Why dont you delegate a LPFM lady,other than the one that scripted you to write this post,and let the delegated LPFM WORKER go drive around miami...and compare the signal strengths of the Various stations that are of the Pirate Type..Then also have someone poll by telephone,various residences whom might be a audience member of the Ethnic pirate radio listening audience,and ask them to tune to which ever station is on the air that is being Signal strength Checked,and ask them if they are able to RX the signal...Then arrive at your own conclusion,and then call the Particular Radio station and advise them that one can Listen to the signal in a car at say XMiLES....But the Coverage however is marginal in a residence(Home) at a even less distance.

Then wait a week or so,and listen for a final definitive answer to your question,by listening to a on the air live broadcast test Signal throw commandered by no other than me..Norman Michael Barrow..The Stack Meister of Signal delivery.

Respects..Storminorm..The CockFighter=Ready to take down all oppositions..Ready for the big fight.....I have spent enough time and money to now realize whom i need to throw back at....lets go bring it on
Mon Jun 21, 2004 4:41 am View user's profile Send private message
Black_Hawk
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Post OR EVEN BETTER YET Reply with quote
IF YOU REQUIRE AN URGENT ANSWER WHY NOT MAKE A FEW CALLS TO NAPLES FLORIDA AND ASK THE HAITIAN CLAN OUT THERE HOW WAS THE COVERAGE OF RADIO NEW STAR..100.5 Megacycles,on the Broadcast dial..especially where the reception in homes and Business was concerned
Mon Jun 21, 2004 4:45 am View user's profile Send private message
NORM B_AXIAL RATIO
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Post Re: Antenna Questions Reply with quote
apollo wrote:
Do the following questions apply to LPFM or are they not applicable?

Is the antenna cable length a factor in antenna performance? I heard one time that ideally the length of the antenna cable should be in even wavelengths of the actual transmitter frequency.

Which antenna provides the best performance for a non-directional application under 100w ERP? Considering, a 5/8 wave vs a single or dual dipole type.

It seems that most antennas listed here are vertically polarized; does that affect the ability of home receiver’s vs car radios?

Thanks for your feedback…


However here a few ideas you all may wanna bear in mind....and also folks for such general questions,one can always do a Web search..I mean everyone seems to have a computer these days.

being the nice fellow that i am bear these facts in mind.

A)Antenna polarization is a very important consideration when choosing and installing an antenna. Most communications systems use either vertical, horizontal or circular polarization. Knowing the difference between polarizations and how to maximize their benefit is very important to the antenna user.

P)An antenna is a transducer that converts radio frequency electric current to electromagnetic waves that are then radiated into space. The electric field or "E" plane determines the polarization or orientation of the radio wave. In general, most antennas radiate either linear or circular polarization.

O)An antenna is said to be vertically polarized (linear) when its electric field is perpendicular to the Earth's surface. An example of a vertical antenna is a broadcast tower for AM radio or the "whip" antenna on an automobile.

L)An antenna is said to be vertically polarized (linear) when its electric field is perpendicular to the Earth's surface. An example of a vertical antenna is a broadcast tower for AM radio or the "whip" antenna on an automobile.
When choosing an antenna, it is an important consideration as to whether the polarization is linear or elliptical. If the polarization is linear, is it vertical or horizontal? If circular, is it RHC or LHC?

On line-of-sight (LOS) paths, it is most important that the polarization of the antennas at both ends of the path use the same polarization. In a linearly polarized system, a misalignment of polarization of 45 degrees will degrade the signal up to 3 dB and if misaligned 90 degrees the attenuation can be 20 dB or more. Likewise, in a circular polarized system, both antennas must have the same sense. If not, an additional loss of 20 dB or more will be incurred.

Also note that linearly polarized antennas will work with circularly polarized antennas and vice versa. However, there will be up to a 3 dB loss in signal strength. In weak signal situations, this loss of signal may impair communications.

Cross polarization is another consideration. It happens when unwanted radiation is present from a polarization which is different from the polarization in which the antenna was intended to radiate. For example, a vertical antenna may radiate some horizontal polarization and vice versa. However, this is seldom a problem unless there is noise or strong signals nearby.

L)Vertical polarization is most often used when it is desired to radiate a radio signal in all directions such as widely distributed mobile units. Vertical polarization also works well in the suburbs or out in the country, especially where hills are present. As a result, nowadays most two-way Earth to Earth communications in the frequency range above 30 MHz use vertical polarization.

Horizontal polarization is used to broadcast television in the USA. Some say that horizontal polarization was originally chosen because there was an advantage to not have TV reception interfered with by vertically polarized stations such as mobile radio. Also, man made radio noise is predominantly vertically polarized and the use of horizontal polarization would provide some discrimination against interference from noise.

In the early days of FM radio in the 88-108 MHz spectrum, the radio stations broadcasted horizontal polarization. However, in the 1960's, FM radios became popular in automobiles which used vertical polarized receiving whip antennas. As a result, the FCC modified Part 73 of the rules and regulations to allow FM stations to broadcast RHC or elliptical polarization to improve reception to vertical receiving antennas as long as the horizontal component was dominant

AND FINALLY;

O)Circularly polarized antennas are normally more costly than linear polarized types since true circular polarization is difficult to attain.

On another note, when radio waves strike a smooth reflective surface, they may incur a 180 degree phase shift, a phenomenon known as specular or mirror image reflection. The reflected signal may then destructively or constructively affect the direct LOS signal. Circular polarization has been used to an advantage in these situations since the reflected wave would have a different sense than the direct wave and block the fading from these reflections.

Even if the polarizations are matched, other factors may affect the strength of the signal. The most common are long and short term fading. Long term fading results from changes in the weather (such as barometric pressure or precipitation) or when a mobile station moves behind hills or buildings. Short term fading is often referred to as "multipath" fading since it results from reflected signals interfering with the LOS signal.

Now for a practical implemantation of all the above then come see me Storminorm..The Cockfighter
Mon Jun 21, 2004 5:42 am
Storminorm
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Post HATE TO SOUNJD SO BOMBASTIC Reply with quote
But hey just waiting for my first Financial deposit to be handed over to me personally..Then i shall really tickle your all RF fantasies with a poundacious delivery of signal qaulity.

Hey let me advise THOSE HAITIAN FOLKS THAT WOULD WANNA ATTEMPT TO DENY ME MY OBJECTIVES..BY USEING METHODS OF TRICKERY AND OTHER MEANS...GO SOMEWHERE ELSE AND THROW DOWN ON WHOMEVER...DONT EVER..EVER LET ME DETECT THAT I AM BEING THROWN AT WITH A VIEW TO HAMPER MY PROGRESS OR THAT OF THE FOLKS WHOM ARE IN UNITY WITH ME ON MY GOALS AND OBJECTIVES.

YOU ALL HAVE A VERY SHORT NOTICE OF CEASE AND DESISTS FROM ATTACKING ME WITH ****** UP' TECHNIQUES..THAT ALSO GOES FOR THE LADIES AS WELL...I WILL STRIP YOU ALL OF YOUR DIGNITY AND POISE IF YOU LADIES DONT RESPECT YOURSELVES..AND ENCOURAGE OTHERS TO FOLLOW SUIT.

IF YOU WISH FOR A FIGHT..I AM READY.

Respects..Norm B..The Cockfighter..You all have only heard about a Rooster...I will show you all what a Rooster is all about.
Mon Jun 21, 2004 5:59 am
Black_Hawk
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Post SO HERE IS THE GIG Reply with quote
On another note, when radio waves strike a smooth reflective surface, they may incur a 180 degree phase shift, a phenomenon known as specular or mirror image reflection. The reflected signal may then destructively or constructively affect the direct LOS signal. Circular polarization has been used to an advantage in these situations since the reflected wave would have a different sense than the direct wave and block the fading from these reflections.
Mon Jun 21, 2004 6:58 am View user's profile Send private message
webmon
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Newbie here. I am looking for an antenna to give me an umbrella over my house (2 story) and not spread to the neighbors.
Ideas / suggestions?
Fri Oct 08, 2004 3:59 pm View user's profile Send private message
DrSandi
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Post Antenna Answers Reply with quote
The biggest single way that antenna cable length affects antenna performance is the signal loss. Every cable has loss, less is better.

Don't sweat the wavelength of the cable vs. transmission frequency. It's mostly esoteric unless you have a really badly tuned antenna and operate at a high power. In that case, you could theoretically melt through the insulation at points about every ten feet (3m) along the cable. Unlikely with LPFM.

5/8 wave is nice. It gives about a 2 dB gain over a dipole (3.4 dBi). A single dipole gives 0 gain compared to a dipole for obvious reasons.

If you have the mast space, a properly spaced dual dipole will give 3 dB gain over a single dipole, or double the power.

Each of these antennas is more or less omnidirectional. They increase power by focusing your signal toward the horizon, reducing signal that goes straight up and straight down to make up the difference.

If you want more power and most of your listeners are in a single direction, consider a low cost Yagi which could give you 4 times the power in one direction by stealing it from the other directions.


Dr. Sandi


[quote="apollo"]Do the following questions apply to LPFM or are they not applicable?

Is the antenna cable length a factor in antenna performance? I heard one time that ideally the length of the antenna cable should be in even wavelengths of the actual transmitter frequency.

Which antenna provides the best performance for a non-directional application under 100w ERP? Considering, a 5/8 wave vs a single or dual dipole type.

It seems that most antennas listed here are vertically polarized; does that affect the ability of home receiver’s vs car radios?
quote]
Fri Oct 15, 2004 3:05 am View user's profile Send private message Visit poster's website
DrSandi
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Post Antenna Polarization Reply with quote
Antenna polarization usually ends up as a battle between the real world and theory.

First of all, if you have power to burn, you should choose circular or elliptical polarization. Commercial broadcasters do this because they have a legal power limit. They want to maximize the signal within that power limit. The FCC and other governmental agencies allow stations to operate at full power in the Horizontal polarization. They additionally allow UP TO full power in the Vertical polarization.

There is clear evidence that circular polarization gives better coverage, particular in bad spots within the licensed coverage area. So if you have lots of power, choose CIRCULAR POLARIZATION.

However, low power operators are usually running as much power as they can afford. In that case, I'd recommend you choose a single polarization and go with it.

The reason most LPFM antennas you see are Vertical is that they're more compact and simpler to deal with.

A horizontally polarized antenna will generally be a loop that is aligned parallel to the ground. This tends to be heavy on the mast, pulling it over in high wind if it's not well guyed. And because of design limitations, they tend to be pretty narrowband. Choose a single channel and stick with it! Designs that aren't loops will be directional. Most people don't want directional antennas.

Vertically polarized antennas can be broadband enough to cover the entire FM band. They are generally more or less omnidirectional. Okay, a vertical dipole has a low spot on the back side that can be about 1/4 of the power of the front side. But it's FAIRLY omnidirectional.

While a vertical receive antenna will pick up a vertical transmit antenna better than a cross-polarized antenna, it's often much less pronounced than the theoretical numbers. This is because here on the ground, signal bounce off hills, buildings and the ground itself. This tends to change the polarization. But not entirely.

In reality, I use VERTICAL antennas such as a dipole or J-Pole. Since roughly half of all radio listening in the U.S. is done in cars, I know that at least half of my audicence will hear the strongest signal. Of the remaining radios out there, many are boom boxes with an adjustable antenna that almost invariably gets tweaked by the listener anyway. They'll set themselves up for the best signal. The only real minus is plug-in radios that use the line cord as the antenna. Those tend to be more horizontal than vertical. But even there, you usually have some vertical component as the line droops down toward the AC outlet on the wall.

As a consultant, I always recommend to my clients that they choose a VERTICALLY POLARIZED ANTENNA.

Circular will not increase your overall coverage, but it WILL fill in nasty holes inside your broadcast range caused by hills or large clumps of big buildings.

Circular is best if you've got the power.


Dr. Sandi
Fri Oct 15, 2004 3:26 am View user's profile Send private message Visit poster's website
Dr. No
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Post Reply with quote
webmon wrote:
Newbie here. I am looking for an antenna to give me an umbrella over my house (2 story) and not spread to the neighbors.
Ideas / suggestions?


I suggest a leaky coax antenna for use at ones home. Take some very cheap low quality RG-58 the kind that has poor outer braid covering.

Use 10 feet and place connectors on each end, hook a small 50 ohm dummy load to one end and the other to the exciter.

Start with 30 milliwatts and increase power until the signal is solid enough all over your home. 30 to 100 milliwatts should cover a home. The placement of the coax can be experimented with also in order to achieve a small footprint more or less within your home. Lower the power a bit if the signal is too strong outside your home.
Sun Jan 02, 2005 2:28 am View user's profile Send private message
Dr. No
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Post Which antenna provides the best performance ? Reply with quote
>Which antenna provides the best performance for a non-directional application under >100w ERP? Considering, a 5/8 wave vs a single or dual dipole type.

I have seen a 5/8 comet beaten by a home made slim jim for about one tenth the cost.
See http://geocities.com/juliusno1776/

The slim jim focuses its radiation in a flatter manner than a 5/8 wave and especially a 1/4 wave ground plane.

Place that savings toward elevating the antenna higher off the ground, or toward a better quality exciter.
Sun Jan 02, 2005 2:45 am View user's profile Send private message
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