Ch 7-51 Outdoor Antennas - AVS Forum
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Old 08-06-2009, 09:59 AM - Thread Starter
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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

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Old 08-06-2009, 11:24 AM
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Probably no difference.

7-13 is still VHF

14-51 will just have a few less elements
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Old 08-06-2009, 12:09 PM
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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.
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Old 08-06-2009, 01:13 PM
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Maybe I missed something but...
How does an antenna gain 3dB for channels 14-51 by eliminating 52-69?
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Old 08-06-2009, 01:28 PM - Thread Starter
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Quote:
Originally Posted by k_ross View Post

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.

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Old 08-06-2009, 10:02 PM - Thread Starter
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A Google search turned up the following post from 01-18-08:
Quote:
Originally Posted by HDTVChallenged View Post

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.


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Old 08-07-2009, 10:03 AM
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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.
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Old 08-07-2009, 10:26 AM
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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.
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Old 08-07-2009, 04:43 PM - Thread Starter
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Are there any ch 7-51 or 14-51 directional antennas currently available?

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Old 08-07-2009, 09:15 PM
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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.
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Old 08-07-2009, 11:00 PM - Thread Starter
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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."


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Old 08-08-2009, 03:57 AM
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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.
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Old 08-08-2009, 06:44 AM
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Quote:
Originally Posted by TV Trey View Post

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.
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Old 08-08-2009, 07:28 AM - Thread Starter
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Quote:
Originally Posted by ProjectSHO89 View Post

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.

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Old 08-08-2009, 08:55 AM
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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.
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Old 08-08-2009, 09:08 AM - Thread Starter
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Currently, AD does not offer a directional 7-51 or 14-51 antenna.

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Old 08-08-2009, 09:20 AM - Thread Starter
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Quote:
Originally Posted by Ratman View Post

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/

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Old 08-08-2009, 09:45 AM
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Grant Whipple is a sales manager, not an engineer...
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Old 08-08-2009, 10:47 AM
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Quote:
Originally Posted by ota.dt.man View Post

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"...
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Old 08-08-2009, 11:24 AM
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Quote:
Originally Posted by ota.dt.man View Post

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?
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Old 08-08-2009, 02:15 PM - Thread Starter
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Quote:
Originally Posted by arxaw View Post

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

Sounds intriguing. Please tell us more.

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Old 08-08-2009, 04:29 PM
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Quote:
Originally Posted by ota.dt.man View Post

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.

Given the same boom length, a 7-51 versus a 7-69 antenna will have no gain increase for the hi-band (7-13) VHF channels. The UHF section might possibly see a .2 to .3 dB overall gain increase due to the antenna's bandwidth being reduced by 108 MHz.
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Old 08-08-2009, 11:05 PM - Thread Starter
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June 10, 2009
Webinar
Presenter:
John Gabrysch,
Electronics Engineer,
Media Bureau, Engineering Division, Federal Communications Commission

PPT slide # 17
Quote:
Analog vs. Digital Antennas
  • Antennas work for both, as long as they cover the correct frequencies.
  • HDTV Antenna is a marketing term
  • Watch out - some are UHF only (usually the small, cute ones). Some marked as combination VHF/UHF have poor VHF performance.
  • Most new antennas designed for channels 7-51
  • Most old antennas designed for 2-13 or 2-69


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Old 08-09-2009, 04:28 AM
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John Gabrysch did not mention any increase in gain. You should go back and read again the #10 post by member Colm.
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Old 08-09-2009, 05:38 AM
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Quote:
Originally Posted by ota.dt.man View Post

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

The C4 is QUITE directional. As much (if not more so) than the DB8 or CM4228.
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Old 08-09-2009, 01:42 PM
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So far, all the new outdoor VHF/UHF antennas that I have seen that are available or have been announced (Antenna Craft, Channel Master, an Winegard) have been for channels 7-69, not 7-51. Why? They are for the most part just modified versions of the channel 2-69 versions. Eliminating channels 2 through 6 is easy with most of them (just eliminate some elements) and shorten the boom. It requires minimal design, testing and retooling work, and it makes the antenna smaller reducing manufacturing and shipping costs and improving curb appeal so more folks will be willing to put one on their house instead of relying on an indoor antenna. That change is a no-brainer. The UHF Yagi section of them could be redesigned for channels 14-51. But that will yield only a very small change in performance or size. There is very little motivation for a manufacturer to change the UHF Yagi section of an existing design in that case. Doing so requires real engineering: design, simulation, testing on the antenna range, and retooling, all of which costs money when the current design works just fine and the net change in manufacturing and shipping costs, and performance, will be minimal.

Will channel 7-51 designs dominate for totally new designs? Of course, 98% of the market is there. But, so far, there aren't any totally new designs because there isn't a compelling reason.

I am curious as to what benefits ota.dt.man expects from an antenna designed for channels 7-51 instead of 7-69. If it is significantly smaller size for equal performance for a given type of antenna, or significantly more gain for the same size and type antenna, it ain't gonna happen. It is basic physics. Yes, you can improve gain slightly when you reduce the bandwidth of a Yagi, but it won't be by a significant amount.
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Old 08-09-2009, 02:06 PM - Thread Starter
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A Google search turned up the following post by an AVS member who is an MDU installer:
Quote:
Originally Posted by AntAltMike View Post

A channel 7 antenna only needs to be about 30 or so inches wide. Nearly all of the lowband transmitters in the largest metropolitan markets are giving up their lowband assignment. In my market, 2, 4, and 5 will be staying on UHF, whereas 7, 9, 11 and 13 will be moving down. I think you'll see a lot of 7-51 antennas. The booms will be nearly as long as they are now, but they will have much less wind load and will last a lot longer.


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Old 08-09-2009, 02:19 PM - Thread Starter
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A Google search turned up the following post by an AVS member who is also a member of the SBE - Society of Broadcast Engineers:
Quote:
Originally Posted by Dr Touchtone View Post

What I dont get is why build an antenna covering 7-69 when post analog sunset, DTVs will only be 7-51???? Has every antenna manufacturer forgotten that 52-69 is going away due to the 700MHz LMR band taking it over? I have a local 64 analog LP.....but I think they will have to move as well even though they are an LP, the 61-69 channels are gone period....or are the upper 700MHz channels allowed LP/translators to remain for now?? I know 51-60 is allowed for LP/xltrs under a no interference exception (THEY not interfer with new services)....but I thought upper 700MHz (61-69) was NO TV at all after analog sunset??


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Old 08-09-2009, 02:32 PM
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You have the answer to your OP. Google all you want
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Old 08-09-2009, 03:25 PM
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I'm looking forward to ota.dt.man providing a list of the "7-51 only" antennas that are available today.

Hopefully some comparison specs will also be provided. If I go to the the effort/expense of swapping out my 4228, I'd like to know if it's justifiable.
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