O/T: Folded Dipole

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On Sun, 26 Apr 2009 17:47:02 -0500, "MikeWhy"

A dipole is not "somewhat directional"--it's absolutely directional. It has its major lobes perpendicular to its axis. It has extreme nulls off the ends. It is, by definition, directional.

A dipole has no gain. In fact, it is the real world reference to which other antennas are compared to determine their gain. The isotropic radiator, while interesting to consider in a theoretical sense, doesn't (and can't) exist. While useful for theoretical modeling, it's sole purpose in the real world is to make an antenna with gain (Yagi, LPDA, rhombic, etc.) seem like it has more gain by making the comparison not legitimately to a dipole, but hyperbolically, to an isotropic radiator.

Nothing more amusing to me than to see the theoretical dBi (decibels of gain in reference to an isotropic radiator, which doesn't exixt) applied to a dipole. Geez, it's a dipole. It has no gain. dBi, particularly when discussing a dipole, is essentially a worthless "value." And to further make the point, when one tosses out the calculated dBi, the antenna used as a reference is almost universally the dipole (dBd). That's why it's so amusing. One might as well say a dipole has zero gain when compared to a...dipole. Duh! can anyone spell tautology?
--
LRod

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Zero similarly doesn't exist in older number systems. Even they learned the errors of their ways, or at least succumbed to natural selection pressures in their own way.
Dipoles have non-uniform directivity. It would make a lousy basis of reference.
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On Mon, 27 Apr 2009 19:12:10 -0500, "MikeWhy"

???
Yet it's the principal basis of reference that's used in the real world of antenna performance measurement. dBi only has relevance in marketing.
--
LRod

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Is the radiation pattern of a dipole uniform in all directions? If not, which single gain value would you use for as the base reference gain? You have this completely backwards. Marketing benefits from a single figure of merit, some "gain" value over a dipole or some other value. It makes sense to you and me as some indication of its performance in presumably the forward direction.
Antennas are passive devices. Forward gain comes from accepting energy from one direction while rejecting energy from other directions. (Simplisticly speaking, since nits count.) By itself, it says very little about the antenna. The single figure of merit is meaningful mostly for marketing. A picture here is worth a few thousand words. Have a look at http://www.eznec.com /.
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On Tue, 28 Apr 2009 04:08:39 -0500, "MikeWhy"

If you don't understand the concepts of antennas (dipoles in particular) and lobes, there is no point in discussing this further.
Go buy those antennas with 2.1 dB more gain (*calculated* against...thin air) than the identical product of their competitor (*measured* against a real life antenna)r. You're a perfect subject for their market.
--
LRod

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Remember way back when the TV experts in the stores preached that you need a COLOR TV antenna for best reception on one of those NEW style Color TV's? They are at it again with the Digital TV's. Our 15 year old rabbit ear antenna works fine on our LCD. I believe that perhaps an old out doors antenna that has been fighting the elements may be out done by a brand new antenna but the digital signal requires no better antenna than analog as you well know.
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With the change to digital comes new frequencies. Your rabbit ears are designed for VHF. The digital transmissions are on UHF. If you are in a strong signal area, your rabbit ears may continue to work. If not, you will need a new antenna.
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I get about 30 channels in Houston however most of the antennas are about 8 miles away "as the crow flies". Oddly with a similar antenna and with an analog TV the reception for 3 of the 5 major network stations was terrible. I added a $50 digital tuner to that TV and with the same antenna the reception was perfect.
My father lives 2 miles from me, added the digital tuner, and a $50 set of "digital" rabbit ears and the reception sucks if you stand too close or too far away. The antenna is located near the ceiling.
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CW wrote:

Some digital is on UHF, some on VHF, just as some analog was on UHF and some was on VHF. Nothing new _there_.
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External rabbit ear antennae have had UHF capabilities for forty years.
scott
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> > External rabbit ear antennae have had UHF capabilities for forty years.
So do your bedsprings but it doesn't make them efficient.
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I had much the same experience a couple of years ago. Really, now, why would you need a new antenna if the frequencies don't change? Jim
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Jim wrote:

Narrower bandwidth at same or less transmit power results in lower received signal strength.
Two other ways of coping with the problem are to use a signal pre-amplifier and using a directional (gain) antenna.
I can't pick up PBS even with a pre-amp, so plan to build a quad antenna that should deliver about 21db of forward gain.
--
Morris Dovey
DeSoto Solar
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Morris Dovey wrote:

The digital receiver only has to determine if the bit is a "0" or a "1" so the signal doesn't have to be as strong as with an analog receiver.
I've got an antenna with a variable pre-amp. Using that antenna I have to turn the gain to minimum to receive anything. Even at minimum some station drop in and out. If I raise the gain I loose the signal completely. I suspect the signal is still being over driven and clipping. A plain old $9 antenna works perfectly on all the stations in my area.
--
Jack Novak
Buffalo, NY - USA
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Nova wrote:

That may be the theory, but if it misses a few bits you get a black screen while with analog you get a viewable degraded image.

Lucky you.
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Are you reading this some where? Do you actually have digital? I have had digital for close to 4 years and if I am getting bad reception the picture is all kinds of terrible, you would swear you were doing mushrooms when this happens.

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Leon wrote:

They've been broadcasting digital signals in the Houston area for over four years???
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Jack Novak
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Satellite has been digital way longer than that. But I have been watching local digital directly from local broadcast with rabbit ear for almost 4 years. It was just a couple of stations to begin with, the local advertising, local news, and day time was in standard. Most prime time was about the only time you could watch in HD.
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Nova wrote:

Yes they have, and most of the rest of the country as well.
And my personal experience with digital is that there's perfect picture, frozen picture, or black screen. I've never seen anything that looks like "doing mushrooms" however I am willing to grant that there may be some sets out there that show pixelation when they lose bits.
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