[ota.dt.man]

For those who are well-versed in antenna design theory:


Now that the FCC has limited DTV UHF channels to 14-51, about how much additional gain would a Ch 7-51 outdoor antenna provide compared with antennas that are designed to receive channel 69?


Thanks

 

[Ratman]

Probably no difference.


7-13 is still VHF


14-51 will just have a few less elements

 

[k_ross]

I guess it depends on the antenna. Some antennas have a steeper slope towards channel 69, while others are flatter. The XG91, for example, has one of the steeper slopes, so it would probably gain about 3dB by retuning if for an upper limit of channel 51.

 

[Ratman]

Maybe I missed something but...

How does an antenna gain 3dB for channels 14-51 by eliminating 52-69?

 

[ota.dt.man]



Quote:
Originally Posted by k_ross /forum/post/16954915


I guess it depends on the antenna.

For the purposes of this thread, let's focus on the most well regarded 7-69 and 14-69 outdoor antennas.

 

[ota.dt.man]

A Google search turned up the following post from 01-18-08:

Quote:
Originally Posted by HDTVChallenged /forum/post/12857229


In the real world, it's probably not a big issue. If the antenna works ok now, it's not going to suddenly crap out when chs 53-69 go way.


OTOH, a pure UHF yagi is designed so that the are most sensitive at the highest frequency (Ch69 currently), the sensitivity decreases (sometimes dramatically) as the frequency decreases. Most real world "yagi" designs include a rear reflector that helps offset the loss at lower frequencies. A lower tuning frequency will result in less gain "loss" at ch14 and perhaps a slightly better gain at ch51.


Edit:


Why tune to the highest frequency you ask? Because the antenna gain rapidly drops to zero dB or less above the tuning frequency.

 

[nybbler]

It's this narrowing which made the Hoverman design practical (thus the Gray-Hoverman antenna). The bowtie people over in the UHF antenna thread are getting a few DB out of it as well.

 

[kedirekin]

For many antennas, gain is at it's greatest at the highest frequency the antenna is designed to receive.


An antenna designed for 14-69 might have, say, 11 dBi gain on channel 69, but be down to 9 dBi at channel 50, and down 7 dBi at channel 20.


By redesigning the antenna for 14-51, you can move that whole range up - you get 11 dBi at channel 50 (2 dB better than the antenna above) and 9 dBi at channel 20 (again, 2 dB better). You still loose gain on lower channels, but the max has been moved down to channel 51 - so the lower channels are closer to the maximum gain.


On top of that, the new 14-51 antenna can be optimized for the narrower bandwidth, getting you another dB or so maximum gain (12 dBi at 50, 10 dBi at 20).


All these numbers are made up, but you get the idea.

 

[ota.dt.man]

Are there any ch 7-51 or 14-51 directional antennas currently available?

 

[Colm]

I don't think you are going to see any significant change in traditional outdoor VHF/UHF antenna design other that what has already occurred. Manufacturers have deleted the elements for the low VHF band. The UHF section hasn't changed much.


I am not an expert in antenna design. But my understanding is that the major factor affecting gain in a Yagi antenna is boom length (which affects the number of directors) relative to frequency. Most of these antennas use Yagis for the UHF section. Unless you change the length of it, you aren't going to get a significant change in gain. It is the short wave lengths that have been eliminated, not the long ones. If there is a peak in gain above channel 51, you aren't going to move it down without making the boom longer.


FWIW not all UHF antennas are peaked for channels above 51. The Winegard Yagis appear to be designed for maximum gain around channel 50. So there is what a channel 14-51 antenna would look like.

 

[ota.dt.man]

A Goggle search turned up the following,
http://demystifyingdigital.com/

posted: June 02, 2009

Quote:
The most popular and most productive TV antennas are geared toward channels 7-51.


Grant Whipple, TV guru at Winegard Antenna Company, told me, "Focusing an antenna on a narrower bandwidth, in this case 7-51 instead of the old 2-69, creates a better performing antenna with more gain."

 

[TV Trey]

Someone should ask Mr. Whipple why his HD8200U (2-69) has exact same gain figures as the HD7698P (7-69). Could it have something to do with boom length??? Note: Same gain for channels 7-69.

 

[ProjectSHO89]



Quote:
Originally Posted by TV Trey /forum/post/16964590


Someone should ask Mr. Whipple why his HD8200U (2-69) has exact same gain figures as the HD7698P (7-69). Could it have something to do with boom length??? Note: Same gain for channels 7-69.

Probably because they haven't brought to market any re-scaled antennas.


Since 51-69 have NOT gone away for North America (observe Mexico, Canada, and LP in the US), don't expect manufacturers to eliminate potential markets just because the US' full-power stations have moved to 51 and below.


To do so just to satisfy the opinions of internet posters while sacrificing potential market share wouldn't be very business-savvy.


AD already has their ClearStream C1, C2, and C4 that are optimized for 14-51 and the C5 that is optimized for 7-13. As far as I've seen, they're the only ones so far that have re-tuned UHF antennas available and on the market.

 

[ota.dt.man]



Quote:
Originally Posted by ProjectSHO89 /forum/post/16964804


Probably because they haven't brought to market any re-scaled antennas.


Since 51-69 have NOT gone away for North America (observe Mexico, Canada, and LP in the US), don't expect manufacturers to eliminate potential markets just because the US' full-power stations have moved to 51 and below.


To do so just to satisfy the opinions of internet posters while sacrificing potential market share wouldn't be very business-savvy.

No one is suggesting that manufacturers eliminate 7-69 antennas if they're needed in other markets. However, it would be greatly appreciated if they would offer re-scaled 7-51 antennas for the US market since the FCC has eliminated 52-69.

 

[Ratman]

Other than size... it doesn't buy you much of a "gain" in performance. Also, probably isn't practical (cost justifiable) for the manufacturer when 2-69 antennas will work just fine for all/any applications domestically or internationally.


If it's that important to squeeze every last drop of potential reception, it appears that Antennas Direct is the only (expensive IMO) solution at this time.

 

[ota.dt.man]

Currently, AD does not offer a directional 7-51 or 14-51 antenna.

 

[ota.dt.man]



Quote:
Originally Posted by Ratman /forum/post/16965274


Other than size... it doesn't buy you much of a "gain" in performance.

Per Grant Whipple, National Sales Manager, Winegard:

Quote:
"Focusing an antenna on a narrower bandwidth, in this case 7-51 instead of the old 2-69, creates a better performing antenna with more gain."

http://demystifyingdigital.com/

 

[Colm]

Grant Whipple is a sales manager, not an engineer...

 

[arxaw]



Quote:
Originally Posted by ota.dt.man /forum/post/16962718


Are there any ch 7-51 or 14-51 directional antennas currently available?

I heard that you may be seeing some new 7-51 antennas "soon"...

 

[Ratman]



Quote:
Originally Posted by ota.dt.man /forum/post/16965335


Currently, AD does not offer a directional 7-51 or 14-51 antenna.

What DO you want? You can:

a) use and install a "traditional" antenna

b) wait for "directional" antennas to be offered by other manufacturers specifically to meet your needs (which is unlikely)

c) use antennas from AD
http://www.antennasdirect.com/clears...FdZM5QodTgpYeg


If you want to get OTA today, that's about all there is based on your desires.


No offense, but I personally don't see the expected "returns/gains" (for perhaps a few dB) by obsessing over a "tuned" antenna... unless you have a specific reason.


BTW... how about those of us that have DT on Channel 6?