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Author Topic: Please don't kill me for this topic: DTV angst  (Read 1780 times)
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« Reply #15 on: January 13, 2009, 11:06:28 AM »

If you are not much more than 25 miles from the TV station then you can use what I use, a 75 ohm coax cable and the antenna end is split so that 6" is used for one side of a dipole like antenna and the sheild is also 6". Spread them out like a dipole and it will work great.  Bill
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N8EKT
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« Reply #16 on: January 13, 2009, 11:12:41 AM »

Since you say you live on a mountain, you may be getting some co-channel that is taking out the desired signal or some other rf interference.
You may also be getting FM signals causing interference.
First, forget about Radio Shack antennas.
They are poor performers compared to the rest of the industry.
If you decide to purchase another antenna, I would highly recommend the Winegard HD-7084P it is a VERY heavy duty made in USA antenna and Solid Signal has them for $90.99.
I have been using one for years and it greatly out performed the Radio Shack VU-190 it replaced on VHF and UHF.
Virtually all other TV antennas on the market are now
poorly made in China.
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W0FM
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« Reply #17 on: January 13, 2009, 12:33:02 PM »

I suspect that the "twinlead-block" you refer to may be an old lightning arrestor.  If you have attached multiple runs of twin lead to the terminals on that block you have done more harm than good.

I had an old Radio Shack VHF/UHF medium range antenna laying in the attic that I had never used.  I popped it open an attached some decent RG-6 to it and ran it to my TV.  I pointed the attic antenna in the general direction of the TV transmitters and have never touched it since.  Perfect DTV reception.

Based on your study, I live about the same distance from the transmitters that you do, and I am in a real hole to boot.

I'd add all new RG-6, lose the "twinlead-block" (whatever it is) and go with a Wineguard, Channel Master or similar, respected UHF antenna.

Good luck,

Terry, WØFM
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W4VR
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« Reply #18 on: January 13, 2009, 02:11:14 PM »

check your connections and antenna directivity.
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N8NSN
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« Reply #19 on: January 13, 2009, 05:52:46 PM »

I checked into where the majority of DTV signals will be in the spectrum.

A good antenna would be able to cover from 550MHz to 850MHz.  Yes, UHF.  and maybe just 4 to 6 elements (LOG) for VHF.  

The poster that talked about only a few low band VHF signals and at low power was spot on.

Here...

I am using a 30 year old Channel Master that I refurbished.  It is at 20 feet above ground and on a Channel Master rotor.

From 5 miles North East of Dayton, Ohio I get many stations from Columbus, Cincinnati, and Dayton.  I also get a couple from Indianapolis, Indiana.  A total of just under 40 channels.  

The antenna has a 300 ohm balanced to 75 ohm unbalanced  "Balun" at the antenna feed point, 50 feet of 75 ohm coax to a 3 way splitter and between 10 to 20 feet to each TV set in the house from the splitter.

Two of the TV sets have RCA converter boxes and one TV set is digital ready with both an analog and digital receiver.  The TV set with both types of tuners built into it has better receive than the converters.  I suspect that the RCA converters are mediocre at best.

If you are using a digital ready TV set with the analog receiver in it as well there should be two separate antenna connectors on the back of the set.  Make sure you have your antenna for digital signals plugged into the right antenna connector.  Also if it is a DTV ready set you have to select which signal to select from the menu.

Good luck and let us know how it goes.

 
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AC5UP
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« Reply #20 on: January 13, 2009, 06:47:29 PM »

I've had remarkably good luck with DTV so far as I'm in a strong signal area, but here's a story that might be useful to someone...

The local market has one DTV signal on channel 10 with all others on UHF. Directivity is not an attribute as the tower sites are scattered around the metro. I do volunteer work with a local senior center and they needed some help getting a Zenith converter box installed. The TV is a ~ 10 year old Panasonic VCR combo item mounted on the wall in a lounge area. They had no TV antenna on it, just a 6' piece of RG-59 hanging loose. On most stations they had a snowy but watchable analog picture. The coax-hanging-loose trick worked very poorly with the Zenith box.

So... I'm going through a stage where I really like full wave dipoles and I built one for their TV. Video carrier on channel 10 is at 193.25 MHz. 936 / 193.25 = 4.8435 feet, multiply that by 12 and we're looking at 58 1/8 inches overall length. Divide that by four and the feedpoint is 14.5" from one end. I used 18 gauge insulated wire and dressed it up with a plexiglas insulator drilled for an F chassis mount.

Pinned the antenna to the wall along side the TV with pushpins and flush with the ceiling. Plugged the coax-hanging-loose into the F connector and it works like a hose. Q-5 on all local channels. The Zenith box also found the PBS station in Eufaula which is approximately 70 air miles south.

I was impressed.

Did the same trick at home and found an LP signal I didn't know was there, local Spanish language channel.

In any case, if you have a mixed bag of VHF-HI and UHF signals that are reasonably strong you may find a simple wire in the attic is all you need. If you're far enough out in the 'burbs that all your TV comes from the same direction a two bay bowtie or Yagi would be the better choice, but for a buck and some bench time the full wave dipole cut for the lowest frequency trick is worth considering...
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K9PU
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« Reply #21 on: January 13, 2009, 08:22:08 PM »

sounds like a shorted antenna connector.  You sure you are plugging it into the right socket?  Are you using the channel 3/4 input or video/audio?  Is there an interference source?  I noticed satellite TV converter boxes mess with one or two channels of DTV.

Good luck.

Scott
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KAISERSOUSE
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« Reply #22 on: January 14, 2009, 06:08:54 AM »

While the problem isn't solved completely...it looks like the majority of the problem is the wiring.

As a test I ran coax from where the antenna enters the house, to the TV i've been using to test in the basement.

300-ohm: 0% signal
Coax: 35% signal...4 out of 9-ish stations came in!

If changing the wiring inside the house had that much effect, I'm thinking that at least replacing the outside wire w/ coax will seal the deal (or at least come close).

I have 1000' spool of thick coax I bought from DX Engineering a while ago. I've used all of 50' of it so far so I'll be buying some connectors and a crimping tool and going to town on the antenna side of things this weekend.  I'll buy a good coax splitter and run coax inside where the twinlead is.  If things still arent completely up to par at that point, I'll look into that non-Radio Shack antenna along with a signal booster.

Its a shame...I know I'm still too much of a newbie to know any better but when I was younger I remember Radio Shack not selling cheap junk.  I guess thats why they're still the first place I think of when it comes to all things RF.  Going in there recently I noticed they are slowly turning into nothing more than a TV/Cell phone store.  

Anyways...thanks for all the tips.  I guess the DTV thing is a good catalyst for repairing/upgrading this type of stuff heh.  Didn't really care about OTA TV before but with these new channels and content coming online....for free...why not? Smiley

Thanks again.
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AA4PB
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« Reply #23 on: January 14, 2009, 10:29:13 AM »

Improperly installed or terminated feed line can cause reflections of the signal on the feed line. With analog this will result in ghosting (multiple images) but you can still get a reasonably good picture. With digital, these reflections cause the data bits to be smeared so that they cannot be decoded thus no picture at all on the TV. Digital is an all or nothing proposition.

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K2FIX
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« Reply #24 on: January 14, 2009, 07:37:49 PM »

You are going to have to go up there.  Sorry.

I suggest dumping all the ancient twinlead.  It has been out there very, very long-in hot and cold, rain, etc.  

Try fresh coax...it's not very expensive for CATV use, not like, say LMR 400 Smiley.

The new UHF antennas are smaller and easier to handle.  One small corner reflector style yagi or bowtie is tiny compared to the old antennas.

You probably don't need an amp.  I'm 40 miles outside NYC and feed three HD sets Off the Air without any amplification with no problems.

If you get some signal off rabbit ears, even a marginal rooftop antenna will get you lock.

Total cost should not be very high-and your existing antenna is clearly amortized.
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W0FM
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« Reply #25 on: January 15, 2009, 11:04:40 AM »

"clearly amortized".  HA!  I love it!

Terry, WØFM
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AC5UP
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« Reply #26 on: January 15, 2009, 07:44:42 PM »

...formerly anodized and now completely amortized.

Wink
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KAISERSOUSE
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« Reply #27 on: January 16, 2009, 12:30:28 PM »

HAHA yeah the antenna is pretty old and from what I'm told its fallen off the roof twice and been put back together just as many times. Its on the list...I'm just waiting for the temps to get above freezing.  Actually at this point I'll take any temp without a "-" in front of the number.

Your advice has been great and I'm sure this will get resolved as soon as I climb up there. Smaller antenna is appealing...we get some pretty hefty wind and ice and as they say the bigger they are the harder they fall (and given its location...the more windshields they take out).
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