need better vhf antenna

[brado]

Here I am:
http://www.tvfool.com/?option=com_wr...b7c842cb038d1e

Currently I have rabbit ears & a loop, RCA ANT200B (& an ANT525 w/ a broken ear). There is a big hill is blocking the main antenna cluster. I can a few channels such as 18 (krma) since they're on a different hill. Occasionally I can get 7 &9. If I could upgrade my rabbit ears and get 7 & 9 I'd probably be happy. Would something like the winegard ss300 be better? It's only 25.75 in wide, is that wide enuf for VHF? Or maybe the Philips MANT950 or RCA ANT806. Also wondering about the winegard gs100, maybe that is flat enuf that it will lay on the mantle below the TV and be unobtusive, but I can't find a good picture or dimensional drawing.

I could pull a coax up into the attic and install the antenna there also. If I'm going to go to that much trouble I'd want to get some of the other channels down to about 30 db NM, at the same azimuth.

Thanks

[mtownsend]

Hello and welcome!

When it comes to indoor antennas, you won't find anything for VHF that does any better than rabbit ears. That's because the long wavelengths of VHF frequencies requires long antenna elements and wide element spacing to work effectively. Rabbit ears are a simple 2 element dipole, and that's about as good as it gets for two VHF elements. To get anything with 4 elements or more, you're talking about something that's too big for "set-top" sized antennas.

If you want more gain, you'll need to go with something bigger, and that means antennas that are more suitable for attic or rooftop installation.



Before we get into bigger antennas, maybe you should check to make sure you're making the most out of your rabbit ears. Rabbit ears will have their maximum gain when the two elements are laid out horizontally, directly opposite each other and equal in length (almost an idea dipole). The fully horizontal position will have a little bit more gain than a "V" configuration. The elements should be kept away from other conductive objects as much as possible.

To optimize gain in the upper VHF frequencies (since you need channels 7 and 9), you'll want to extend the elements until they are about 40-45 inches tip-to-tip in their horizontal position. If you extend the elements longer than that, you'll actually be tuning the antenna to even lower frequencies (i.e., lower VHF).



Your strongest channels are very strong, and that makes me worried about amp overload. If possible, make sure you're not using any amplification in your setup. An overloaded amp can make things worse rather than better.



If none of this is helping you enough and you're ready to consider an attic or rooftop antenna, then I'd recommend going with An Antennacraft HBU-33 or Winegard HD7694P. Don't use any amplification. These antennas are very likely going to get you down into the 30 dB NM or better.

[Dave Loudin]

Hello. mtownsend has given you solid advice. If you have the possibility of an attic install, you might consider a home brew solution documented here. The advantages of this bow-tie array (NOT the youtube design!!!!) are:

relatively broad receive pattern
positive gain at high-VHF (the same as, or better than, a dipole)
ease of construction

Good luck!

[brado]

Thanks to both of you.

I've tried the rabbit ears horizonal at 40 - 45 in, and also tried them at 78 - 84 in. I read the 40-45 somewhere else also, but here:
http://www.hdtvprimer.com/ANTENNAS/R...s.html#Getting
it says 78 - 84? Why the difference of opinion?

I set them up perpendicular to the LOS and tried various rotations, and positions in the room, but nothing seemed to work consistently until I put them on a chair in from of the metal gas fireplace. Chan 9 comes in very well no matter what I do with the rabbit ear length! It must be acting as a reflector? I'll play around later and see if 7 will come in with a little tweaking of the position. Thanks for the antenna suggestions, I'll probably bit the bullet and put one in the attic.

Dave, Thanks for the DIY option. It looks like a fun project, but not enuf time for that right now.

Thanks

[brado]

One more question. Are the gain claims btwn winegard and antennacraft apples to apples? I noticed that the the winegard has a little better gain but is a little smaller.

[Dave Loudin]

Originally Posted by brado

Dave, Thanks for the DIY option. It looks like a fun project, but not enuf time for that right now.

Thanks

The person who figured all this out has updated his information here. You can order pre-made parts that you can slap together in no time.

[brado]

To get from my attic to TV it's about 32 ft. Should I just buy a premade 50 ft cable, or a 32 ft w/ twist on connectors? In other words, which is worse, the extra 18 ft, or the twist on connectors? With an attic attenna, do I need to run grounding wire?

[mtownsend]

Originally Posted by brado

I've tried the rabbit ears horizonal at 40 - 45 in, and also tried them at 78 - 84 in. Why the difference of opinion?

The difference is in the orientation of the elements. Rabbit ears achieve their best gain when the elements are exactly opposite each other (an ideal dipole). When the elements are tilted up into a "V" configuration, the maximum achievable gain is less. Since the effective electrical resonances also change when you do this, the individual elements must be lengthened in order to get the peak resonance to occur at your desired channels. Even when tuned this way, the "V" configuration will not get as much gain as the horizontal configuration.

Are the gain claims btwn winegard and antennacraft apples to apples? I noticed that the the winegard has a little better gain but is a little smaller.

Yes, I believe they are using the same scale. There are commonly two ways to count antenna gain. One is to use dBd (decibels relative to an ideal dipole), and the other is to use dBi (decibels relative to an ideal isotropic antenna). I believe that both Winegard and Antennacraft data sheets specify dBd as their units.



For future reference, if you ever need to compare dBd gains to dBi gains, then you can take the dBi number and subtract 2.15 from it to get the equivalent dBd number.

Most antenna makers choose to use dBd as their reference. dBd specs tell you how the antenna compares to a properly sized dipole antenna (cut to the optimum length for the frequency in question). Positive numbers indicate more gain than a dipole antenna, and negative numbers indicate less gain.

Isotropic antennas are hypothetical antennas that are completely omnidirectional in every possible direction (front, back, left, right, up, down, etc.). These hypothetical antennas don't really exist, and are mostly used as a point of mathematical comparison when using antenna modeling software to compute the gain of an antenna.

The difference in gain between a dipole antenna and an isotropic one is 2.15 dB. Some antenna manufacturers might publish dBi numbers because they come out 2.15 dB higher than the equivalent dBd numbers. Maybe they do this because their gain figures are derived from computer models as opposed to using calibrated measurements in a lab against a reference dipole antenna. Maybe they do this to publish higher gain numbers to fool consumers that don't know the difference between dBi and dBd specs. Whenever in doubt, check if the gain spec is against an isotropic or dipole antenna.

To get from my attic to TV it's about 32 ft. Should I just buy a premade 50 ft cable, or a 32 ft w/ twist on connectors? In other words, which is worse, the extra 18 ft, or the twist on connectors?

RG6 cable loses about 5 dB of signal for every 100 feet of cable. The 18 foot difference you're talking about is less than 1 dB of signal, so I'd say the difference is not enough to sweat over.

Making your own cables is nice, but it does add a little bit of hassle. The quality of connection will depend on your ability to make a clean connection of the connector to the outer conductor of the coax. If you do not have much experience with this, then I'd recommend saving yourself the trouble and just get a pre-made cable.

With an attic attenna, do I need to run grounding wire?

No you do not.