Antennas - Directional or Omni?
 

Antennas - Directional or Omni?

Started by pickpaul, March 31, 2009, 02:14:21 PM

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pickpaul

March 31, 2009, 02:14:21 PM
Does anyone have any comparative experience with the two types for TV reception. Obviously Directional would be better in a marginal environment but you need to know where to point it as with new digital you can't just tweak the direction while watching the snow on the screen I guess. Omni seems like the no hassle option but is it a good enough signal to use most of the time? Any help would be great.

Cheers, Paul.

JohnEd

#1
March 31, 2009, 04:24:37 PM
That "bat wing" looking antenna that cranks up and down is superb.  You do have to slew it to point at the signal for the best signal.  It also has an RF amplifier built in that actually works....not a gimmick.  Allows you to view weaker signals.  See Camping World on line.

The problem with omni is that you get all the signals and their reflections/bounce signals.  That leaves you with ghosts.  Directional antennas beat that problem and can be sensitive to much weaker signals than an omni. 

I would not have believed that hokey looking thing would actually work worth a darn but it has exceeded any expectation I might have had for ANY antenna.  Don't forget to crank it down when you break camp as it is a poor battering ram or tree trimmer.  Don't ask!

HTH,

John
"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
"We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light."
—Pla

Sean

#2
March 31, 2009, 04:25:18 PM
Paul,

You seem to have answered your own question.

Directional antennas such as the Yagi type have a much higher gain, and so you will be able to pick up more distant stations than with an omni, if you can aim the antenna correctly.

Fortunately, that's usually pretty easy;  marginal signal areas are generally away from city centers, and the correct direction can be approximated just by knowing which direction the center of the nearest city lies.  In those cases where you are between two or three cities, you may have to try each of several compass points and see what channels you get.

Alternatively, you can get a signal strength meter to help you aim the antenna, such as this one:
http://www.solidsignal.com/prod_display.asp?PROD=DIGIAIRPRO

Lastly, some models of HDTV sets have built-in signal strength meters to help you align your antenna, typically accessed through the "setup" menus on the set (try under "initial setup," "antenna alignment," or similar).

Of course, if you just don't want to hassle with a directional antenna, there are several models of amplified omni-directional antennas with fairly high gains.

Right now, most digital signals are in the UHF band, so I would choose an antenna optimized for UHF over VHF.  FWIW.

-Sean
http://ourodyssey.blogspot.com
Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com

Sean

#3
March 31, 2009, 04:35:40 PM
Quote from: JohnEd on March 31, 2009, 04:24:37 PM
...  You do have to slew it to point at the signal for the best signal. ...
The problem with omni is that you get all the signals and their reflections/bounce signals.  That leaves you with ghosts.

John,

We were, apparently, typing at the same time.

I think you are talking about analog TV -- digital signals are immune to "ghosts."

What is behind the question is that, on June 12, when the old analog stations go dark forever, there is no convenient way to "aim" the bat-wing style you are talking about.  Digital stations either come in clearly, or not at all, and since your new HDTV needs to "scan" the airwaves before use to find which frequencies are available where you are parked, there is no way to, say, tune a station you know to be within range, then rotate the antenna until the station "comes in."

Until June 12, you can mostly turn the bat-wing until a couple of local analog stations come in "well," then have your set scan for digital stations, and things will mostly work OK.

-Sean
http://ourodyssey.blogspot.com
Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com

JohnEd

#4
March 31, 2009, 04:55:41 PM
Sean,

Yes, I was talking analog as that is the only signal I have ever received.  I follow your post and what you are saying is clear to me.  You know that there is a "but" in there....right?

Here is what rubs me:  Every roof top antenna I have ever seen has been a variation of a log periodic or dipole(array).  The log is a highly directional antenna with lotsa gain.  If I follow your discussion and conclusion correctly then all those roof top antennas are obsolete and non functioning come June 12.  This would have made the papers.....or so I am thinking.  A directional antenna on an RV is the same as a directional antenna on a house.(that was a smart @$# way to say that but anything for humor)  Logical?

You gave me a lot of info.  Namely that reflected signals will only interfere if the modulation is analog.  Does the digital have a carrier or does the Rx generate it like in FM?

Thanks,

John
"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
"We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light."
—Pla

JohnEd

#5
March 31, 2009, 05:06:22 PM
Sean,

Camping world is still selling those "Bat wing" Winegard crank up antennas....and they are on sale.  They even have a UHF accessory clamp on antenna.  Both of mine did gang busters with VHF and UHF...analog, to be sure.  Am I contradicting you?  Certainly NOT.  I am confused though.

See:  http://www.campingworld.com/shopping/item/winegard-batwing-sensar-iii-antenna/26655

Thanks,

John
"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
"We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light."
—Pla

Don4107

#6
March 31, 2009, 05:15:50 PM
The redneck solution to pointing your antenna, see where others are pointing them.

Don 4107
Don 4107 Eastern Washington
1975 MCI 5B
1966 GM PD 4107 for sale
1968 GMC Carpenter

Sean

#7
March 31, 2009, 05:20:04 PM
Quote from: JohnEd on March 31, 2009, 04:55:41 PM
... Every roof top antenna I have ever seen has been a variation of a log periodic or dipole(array).  The log is a highly directional antenna with lotsa gain.  If I follow your discussion and conclusion correctly then all those roof top antennas are obsolete and non functioning come June 12.  This would have made the papers.....or so I am thinking.

Existing rooftop antennas will not become obsolete, because, as I wrote earlier, the directional antennas have more gain, if they are pointed in the right direction.  Since most stations are simply installing the digital antennas on the same towers they already use, an existing rooftop antenna will already be properly oriented (assuming it was correctly oriented for the analog signals).  Incidentally most home TV antennas are not log-periodic, but rather simple yagi designs.

There is one respect in which existing home antennas are probably sub-optimal for digital reception, and that is the simple fact that the vast majority of them are optimized for VHF reception, which is where the bulk of metropolitan mass-market TV signals have lived for decades, with UHF reception being a compromise (if not an outright afterthought).  By contrast, most digital stations broadcast on UHF, at least right now (while VHF is still being used by the analog stations), and, due to bandwidth limitations and adjacent-channel issues, UHF will continue to be the principal band for digital signals in the future.

Now here's the rub -- new installations of directional home rooftop antennas made after June 12 will have the same issue I described -- you need to fgure out where to aim the antenna.  In a suburban neighborhood, no problem -- just look at half a dozen of your neighbors and see which way their antennas are pointing.  If you are out in the sticks, you need to use a signal meter or the "guestimate" method I mentioned above.

Quote
A directional antenna on an RV is the same as a directional antenna on a house.

Well, not really.  The key difference is that a house doesn't move, so once the antenna is originally aimed and the HDTV or converter box has "scanned" for channels in the area, you are done, and never have to do it again (although, given that new digital channels are coming on the air all the time, it is recommended that you re-scan for channels periodically, say once every few months).  By contrast, an RV is constantly having to re-deploy and thus re-aim the antenna.  And every time you move the RV more than a few miles, you will need to re-scan for channels, because they are different from city to city.  Digital TVs generally do not let you click from channel to channel among all channels in the spectrum (although a small handful have this capability).

Quote
... reflected signals will only interfere if the modulation is analog.  Does the digital have a carrier or does the Rx generate it like in FM?

Even FM has a carrier.  You might be thinking of SSB.  In any case, reflections can and will interfere with digital signals, however digital sets will either see a good signal and give you a near-perfect picture, or not enough good signal and give you nothing at all -- you can't get a "ghost."  When signals are "marginal" (meaning right on the threshold of what the set can receive and process), you will get alternating perfect picture with nothing, and the transition between them looks like "pixelation."  The picture and audio, in other words, become "choppy."  As a user watching the set, you can't determine whether this is from interference (including signal reflections), or just being too far from the station.

The digital nature of the signal does, however, mean that sophisticated DSP chips inside modern sets can and will find, process, and reject weak time-delayed versions of the stronger signal on the channel, so reflections are not nearly the problem they are with analog.

-Sean
http://ourodyssey.blogspot.com
Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com

Jerry32

#8
March 31, 2009, 06:00:13 PM
I tested the batwing add on unit which makes parasetic directors on the batwing and had it set on a translator signal channel 30. The add on added 6 db to the signal when installed and pointed the proper direction Jerry
1988 MCI 102A3 8V92TA 740

pickpaul

#9
March 31, 2009, 06:28:59 PM
Wow! You guys are amazing, so much info in a few hours!

I think given the benefits/challenges of digital, omni seems like the best compromise.

JohnEd

#10
April 01, 2009, 03:29:04 PM
Pickpaul,

Let me know where you find an omni antenna for an RV.  I came up empty.  Maybe new stuff is on the way.

John
"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
"We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light."
—Pla

JackConrad

#11
April 01, 2009, 04:07:37 PM
Several friends have purchased a small antenna at WalMart, made by Phillips that is about the size of a carton of cigarettes and comes with an amplifier.  Sells for about $50.  I do not know if it is directional or amni, but all 3 are very happy with the antenna's performance.  (2 are on RVs, 3rd is on our rental cabin)Jack
Growing Older Is Mandatory, Growing Up Is Optional
Arcadia, Florida, When we are home
http://s682.photobucket.com/albums/vv186/OBS-JC/

Sean

#12
April 01, 2009, 04:41:41 PM
Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com

WEC4104

#13
April 01, 2009, 07:11:50 PM
When it comes to aiming the antenna to pick up digital signals, there are some television features that can help.  First, you don't have to rely on the "auto program" feature to search the entire band for available stations. With digital television, that's a lot of searching, and you could be looking at 20 minutes or more to complete the process.   If you use  www.antennaweb.org  and plug in your location, it will tell you the available stations (and directional heading)    If you are just looking to pick up one channel, you can use the TV's add-a-channel function, rather than reprogramming the entire channel listing.

On my set (Sony) there is a diagnostics setting in the set up menu that lets me display the antenna signal strength.  Turning that on allows me to fine to the direction of the antenna for digital signals.
If you're going to be dumb, you gotta be tough.
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