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Topic: Over the air HDTV antennas - recommendations?

Ron Funderburg
Jedi Master Film Handler

Posts: 814
From: Chickasha, Oklahoma, USA
Registered: Nov 2007

posted 02-07-2008 11:55 AM

I am not sure Bobby I list tons of stations but only NBC, CBS, Fox, The pbs stuff and some religious channels come in all out of OKC but my outside high def antenna isn't out side it is up in a window frame because I don't have a poll to put on yet! My bad on that! ABC out of Oklahoma City isn't received by any of the people in the Chickasha area on the digital signal.

Oh I need to get that darn poll up and get the antenna out of the house!

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Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 02-08-2008 04:19 AM

I have had the very same problem with amplified antennas (in fact that same Terk or Trek or some such that Joe has -- call it Drek) and like Mitchell, it is hardly worth the effort. It amplifies everything -- signal and noise -- which is as good as nothing.

I was told that a GOOD UHF outdoor antenna is all you need to pick up HDTV. Years ago one UHF station went PBS and I wanted to watch it but I was getting terrible reception with my combo antenna (you know....90% worth of UHF elements and a wussy little 10% piece of crap stuck on the end of it for UHF). I wrote to the FCC asking what to do and they sent me a pamphlet (my tax dollars at work) that explained that UHF reception needn't be inferior to VHF reception if you have the right antenna. They directed me to get a UHF-only antenna with a four bow-tie array behind a screen grid. It's been working great ever since. I am hoping when I finally hook up my Sharp LCD HDTV, I won't have to change anything and this UHF antenna will do the trick.

Luckily I have a clear view of the Empire State Building which is only like 5 miles away as the birds fly....that's practically a direct wire from the transmitters to my TV. Alas, I used to have the same line-of-site to the WTC towers.

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Joe Redifer
You need a beating today

Posts: 12859
From: Denver, Colorado
Registered: May 99

posted 02-08-2008 06:06 AM

quote: Frank Angel
I have had the very same problem with amplified antennas (in fact that same Terk or Trek or some such that Joe has -- call it Drek) and like Mitchell, it is hardly worth the effort. It amplifies everything -- signal and noise -- which is as good as nothing.

I'm not sure who you're responding to, but as I just said the amplification does indeed help the digital signal. Who cares about analog signals? Nobody.

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Mark Strube
Master Film Handler

Posts: 322
From: Milwaukee, WI, United States
Registered: Feb 2007

posted 02-08-2008 06:26 AM

This is a very good place to start... shows you what type of antenna you'll need based on your location compared to the transmitters in your area's locations.

http://www.antennaweb.org

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 02-08-2008 10:16 AM

quote: Joe Redifer
I'm not sure who you're responding to, but as I just said the amplification does indeed help the digital signal. Who cares about analog signals? Nobody.

Joes is correct on this... a little amplified noise hitting a digital receiver is irrelevant. Most DTV's can make a great picture and sound with very little signal...

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Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 02-08-2008 11:03 AM

Question: since the vast majority of OTA antenna inputs on TV receivers require 75 ohm impedence, how come almost all antennae are balanced at 300 ohm which then need a those crappy little transformers made in China which have to have a good deal of inherent loss, especially given how precious is the signal you are trying to capture. Why not just construct the antenna itself as being 75 ohms thus eliminating any need for a matching transformer going into the 75 ohm coax?

Joe, I was agreeing with Mitchell about the bad luck he and I have had with amplified antennas over the years on analog OTA signals. One of those that I had tried was the Trek antenna and it was rubbish....again, for analog TV.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 02-09-2008 01:49 PM

Well, I guess if you do buy those matching transformers that are made in China they are probably going to have alot of loss... and probably alot of lead in them too [Big Grin]

. Truth is that you can still purchase decent 300:75 ohm matching transformers if you seek them out. Also using RG-6 coax for the UHF feed is mandatory if you look at the losses in RG-59 at the UHF frequencies. Keep in mind however that a couple db signal loss with DTV is not going to matter one iota.

Mark

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Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 02-10-2008 02:27 PM

Understood, Mark, but that still begs the question -- why make all antennas with 300 ohm impedence when the vast majority of equipment wants to see 75ohm input and almost all installations will use 75ohm downlink cabling? It would be like all microphones being made with 10K outputs and requiring everyone who uses them to put a transformer to drop them down to 600 or 150 ohm input. Constructing an antenna with a 75ohm impedence to match the equipment that it's expected to be connected to would be a very simple and logical change, and I would imagine, fairly inexpensive. Unless there is some specific reason that 300ohms works better to gather up the signal or perhaps it's more practical that 75ohm (could 75ohm require too large elements?...I have no idea how the impedence is physically constructed).

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Paul Mayer
Oh get out of it Melvin, before it pulls you under!

Posts: 3836
From: Albuquerque, NM
Registered: Feb 2000

posted 02-12-2008 02:22 AM

quote: Frank Angel
Why make all antennas with 300 ohm impedence when the vast majority of equipment wants to see 75ohm input and almost all installations will use 75ohm downlink cabling?

'Cause it's cheap! The easiest/cheapest antennas to make and install at VHF frequencies are folded dipoles, which have a characteristic impedance of 300 Ohms. After WWII when TV began to proliferate, the antennas most available were various versions of folded dipoles. Along with them came 300 Ohm flat twin-line cable, which was almost a perfect match impedance-wise. TV sets had 300 Ohm inputs. What could be simpler ey?

Once cable came along, using a coaxial construction with a nominal impedance of 75 Ohms instead of 300 Ohm flat line, TV sets started to come with 75 Ohm coaxial inputs. Those still using outdoor antennas had to resort to using the 'baluns' mentioned above. (balun = BALanced-UNbalanced. These little transformers convert between 300 Ohm balanced lines and 75 Ohm unbalanced lines).

To me, one of the ironic things about the switch to digital TV is the notion of having to at least consider using an outdoor antenna to get a usable signal. I haven't bought a TV antenna in several years - maybe a new trend with the more expensive ones will be to include a balun at the array, thus making it easier to just use 75 Ohm cable for everything else at the RF end of things.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 02-12-2008 02:51 PM

quote:
'Cause it's cheap!

Thats not the real reason... its because its almost lossless at the higher frequencies. It is however not shielded. In some areas you can use 300 ohm down lead but in large cities its not practical because of the large amounts of RFI. Mounting the 75:300 ohm tranny at the antenna and running RG-6 down to the set is a wise thing to do. Some combo antennas have plug in boards on them that offer you the option of either 300 ohm or 75 ohm down lead. For DTV though where other RFI might not matter much 300 ohm down lead might be very acceptable.

Mark

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James Westbrook
Phenomenal Film Handler

Posts: 1133
From: Lubbock, Texas, Usa
Registered: Mar 2006

posted 02-13-2008 02:34 AM

I wish there was an INDOOR antenna solution to receiving digital signals, especially since I can literally SEE the transmitting towers from my house!
I am seriously considering abandoning broadcast tv.
I can live without CSI.

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Jesse Skeen
Phenomenal Film Handler

Posts: 1517
From: Sacramento, CA
Registered: Aug 2000

posted 02-13-2008 01:07 PM

I recently got a new DVD recorder with a digital TV tuner (I bought it for transferring old tapes and stuff to DVD, not to record TV shows) and I have a cheap indoor antenna from Big Lots that gets all the local digital stations fine, not that there's anything to watch on them. I was disappointed that the tuner outputs the sound as 2-channel PCM instead of Dolby 5.1.

One station here runs a network called Qubo which is kids' shows 24 hours a day; I'd watch that a lot if it didn't have annoying crap on the screen during the shows. There's too many digital artifacts on most channels too, I'd be pissed if they were showing something I cared about.

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James Westbrook
Phenomenal Film Handler

Posts: 1133
From: Lubbock, Texas, Usa
Registered: Mar 2006

posted 02-13-2008 05:33 PM

My current antennas are from Radio Shack and Target, so I should (theoretically) be okay, then...
I got on the CEA website linked above, and here is why I would insist on an indoor antenna: Note that I am on flat ground out here, no mountains (unlike Lubbock in The Buddy Holly Story), no obstructions between me and the towers:
ABC affiliate 5.0 Miles
NBC affiliate 4.7 Miles
PBS affiliate 1.9 Miles (On campus of Texas Tech, which is Northeast of me, the other towers are southeast.)
Fox, CW, My Network TV, Telemundo 4.8 Miles
CBS 3.7 Miles.
If these can't be pulled in by an indoor antenna, then I would feel something is terribly wrong. My house is not built of concrete nor cinderblock, the studs are all wood...
If the indoors don't work in my situation, I'll just not watch tv. I seldom do now. There are NO new episodes of CSI out now, nor will there likely be for 6 weeks...most everything else is crap anyway.

EDIT: Later this same day, I went to Wal-Mart to get my dog some food. I stroll over to electronics. The Digital-to Analog converter boxes are there, Magnivox and RCA. Both priced the same. ($49 and some change.) I buy the Magnivox.
After I hook it up to my Radio Shack Indoor antenna, the picture quality IS better than over-the-air analog broadcasts. 3 channels of PBS, NBC and it's Weather-Plus, Fox and it's Acuweather, ABC and CBS. Funny thing is the CBS affiliate will "tile up" when a truck goes down the street by my house. This same station acted up on analog when a truck went by the house.
CW, MNT, Telemundo and Univision still not accounted for, but I assume these will eventually show up.
I am content.

[ 02-16-2008, 04:45 PM: Message edited by: James Westbrook ]

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Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 03-08-2008 01:04 PM

OK, so 300ohn had excellent characterists in terms of loss-less transmission but is a crap in most places because it isn't shielded. So how come they can't make a shielded 300 ohm cable, like the dual-core that Belden makes so it avoids RF junk?

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 03-09-2008 05:15 PM

quote: Frank Angel
So how come they can't make a shielded 300 ohm cable, like the dual-core that Belden makes so it avoids RF junk?

Its possible that something like that may exist... I never looked. At any rate RG-6 is made in such huge quantities that even adding the cost of a good 300:75 ohm transformer to your downrun would still be alot cheaper. I tend to believe that the 300 ohm shielded cable would also be pretty large in diameter. When ever you add a shield you have a capacitor which gives you loss at high frequencies per foot of cable. Cable is specified in pf of capacitance per foot... Any capacitance added will cut those higher frequencies and those signals may be weak to non-existant at the other end of the cable.

A g9ood example of what capacitance does was fpound when I was in chgarge of A-V repair at Wheaton School District. I had to completely re-wire many of the schools master antenna systems because the contractors cheaply installed RG-59 coax... RG-59 has alot of capacitance to say the least and none of the UHF channels made it further than perhaps two rooms distance from the distribution amp... Some of these systems had Jerrold down convertors on them to convert UHF channels to a VHF frequency just so they could have some usable UHF channels... At any rate I replaced all that RG-59 with RG-6 in probably a dozen school buildings... one principal whose system had never worked told me I was the umpteenth person to try to fix it and he actually bet me dinner that I couldn't fix it. Well.. replacing the cable in his building fixed it... a huge Weingard VHF/UHF antenna on top of his 4 story school building also got him several channels in Indianopolis. We used a larger Jerrold distribution amplifier and attenuated the signal feeding each hallway and at each outlet to 1000uv. He bought me dinner. They tore his school down three years later and built a new one... [Eek!]

Mark

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