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Author Topic: weak signal TV  (Read 10718 times)
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WA1GFZ
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« on: November 29, 2008, 02:05:52 PM »

We have been watching a little 12 inch TV at the beach place that worked OK on rabbit ears and looked bigger if I wear my glasses. Yesterday my brother lugged a spare 27 incher much newer so we would have something nicer to look at. He warned it may not work well on rabbit ears but WTF it was worth a try and I'm planning an antenna in the attic anyway. Sure enough the new tv could barely lock on to the strongest signal. I then moved the new rabbit ears to the old set and it continued to work fine. The signal was either there or not which made me think there was some sort of digital processing going on. The old 12 inch analog would fade in and out where the newer set would go black when the signal got too weak. I guess they cheaped out the front ends forcing users to get cable. This happened to my brother when he upgraded having a hill between his place and the local stations.
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steve_qix
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« Reply #1 on: November 29, 2008, 06:47:27 PM »

I have experienced a similar thing with some newer TVs.

The tuner in my DVD/HardDisk recorder is MUCH more sensitive than the one in the accompanying TV set.

I have found a good, low noise, mast mount type booster amp helps a lot.  Some of these are quite good, and are better than the front ends in any TV I've used so far !!  No cable here, so a strong off-air signal is crucial, and also helps in the DTV arena.
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WA1GFZ
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« Reply #2 on: November 29, 2008, 08:03:44 PM »

Steve,
Any suggestions on antenna located amps. I was thinking of building one with a good low noise MMIC and a little LC filtering. I wonder if it would work with wabbot ears?
It newer set pulled in more stations but the picture quality was poor on all of them.
When we stayed in the local motels before we built we quickly found the local cable system sucks.
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KA1ZGC
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« Reply #3 on: November 30, 2008, 07:48:25 PM »

The old 12 inch analog would fade in and out where the newer set would go black when the signal got too weak. I guess they cheaped out the front ends forcing users to get cable.

If you were watching good ol' NTSC broadcasts, then that's just the TV's squelch circuit doing its thing. They all have them now. It's defeatable on most sets. It's turned on by default because most people don't like white noise blasts when they accidentally switch to an unoccupied channel. They almost all have on-screen menus, and most of those allow you to switch off the weak-signal blackout.

The front-end sensitivity of modern sets is not much worse than it ever was. Some TVs just suck worse than others, but that's nothing new either. The manufacturers don't give a damn if you're plugging your TV into rabbit ears, cable, sattelite, or your neighbor's dog; just so long as you buy their product.

I'd hold off on building an amplifier until they finally settle the allocation issue (if they haven't already). Many stations are petitioning to keep their old assignments after the changeover. Some might stay on their original VHF channels, some might stay on their current UHF assignments. Last I heard (quite a while ago), that was still up in the air. It would suck to build a UHF preamp only to find out your local stations petitioned to keep their VHF channels and won. All that G-10 for nothing!

No reason a single decent JFET wouldn't give you all the boost you need. Nothing fancy needed, just a very broadband stage of gain. 12-15dB of gain will go a long way. A GaAsFET would be complete overkill, and they go casters-up every time lightning strikes within the same hemisphere. Amplifier noise will be less of an issue after February, since you'll only be watching digital TV (with the exception of LPTV stations and translators, who aren't required to change to ATSC).

A preamp should work with rabbit ears just as well as it would with any other antenna you plug into it, provided you shield and bypass it well enough to eliminate feedback paths.

...for what that's worth.
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WA1GFZ
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« Reply #4 on: November 30, 2008, 08:58:05 PM »

Tom,
Yes the new set seemed to have a squelch action.
I was thinking of a low noise MMIC amp. 3 caps maybe 4 and a resistor.
Heck I know I have some CATV amps but they run a fair amount of power.
Then use a wall wart off computer speakers to power it. It would be very easy to remote power it just short the output cap and run power up the coax. I want to put an antenna in the attic on a rotor. I ran plastic pipe through the walls for the cables. I'll try the wabbit ears first. tnx
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WB2YGF
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« Reply #5 on: November 30, 2008, 09:44:18 PM »

I was looking at this puppy - kinda like the homebrew look/quality - a bit pricey though.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280289577274
http://www.kitztech.com/

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John K5PRO
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« Reply #6 on: November 30, 2008, 10:06:03 PM »

Winegard makes a good line of preamps, UHF, VHF, FM, both. They have balanced input (or use a balun on the front end) to fit right at their antenna terminals, 300 ohm feed. They also have 75 ohm in/out versions. I have an AP4700 or 4800 (19 or 28 dB gain) on a single ch 50 UHF yagi up on my old tower. It has been there 10+ years never failed. On my Winegard VHF antenna, I have the built-in model (300 ohm input). Since i am 60+ miles from the transmitters, in a valley with mountain in the way, I still get usable signals. Without preamps, would have nothing. We don't need no stinkin' cable or satellite dish. Waiting for Feb 2009 to determine what the final configuration will be here.

I'd easily buy another Winegard, few dB noise figure.
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WA1GFZ
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« Reply #7 on: December 01, 2008, 08:46:10 AM »

John,
I have to cover about the same distance to N.Y. and Hartford stations.
TNX fc
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WA1QHQ
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« Reply #8 on: December 01, 2008, 09:47:27 AM »

I noticed with the coming of HDTV a resurgence in people wanting to receive their HD broadcast direct off the air. This may be due to cable and satellite companies charging a premium for HD service or as I would like to think people are getting sick and tired of the excessive compression that these companies are employing and want to view the superior quality that the terrestrial broadcast will have. At any rate there seems to be a lot of new antennas coming out on the market that are marketed as HD antennas but should work OK fine on any old TV as long as it works in the range of channels you are trying to receive. I think these antennas actually work unlike some of the juck that has been marketed in years past.
As far as commercial preamps go just make sure the noise figure is not the same as the gain, I actually saw this on a commercial preamp that was for sale at one of the discount stores, got a good laugh when I read the specs on the box.
I have also noticed a trend toward silicon tuners in TVs rather than the old discreet component tuners, don't know if these are any worse than the discreet tuner just lower cost.
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WA1GFZ
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« Reply #9 on: December 01, 2008, 09:56:04 AM »

Mark,
 I think the old discrete tuners had tuned RF stages
The cable co down by the shore sucks so have no desire to interface.
My neighbor just put up a dish.
I have a bunch of HP MMIC amps that are low noise, maybe a couple dB.
Heck maybe try one of my Q bit amps that are even better.
Radio Shack has a number of interesting antennas and I'm told they work well.
The best one is around $100 and I think I can swing it in the attic.
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KA1ZGC
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« Reply #10 on: December 01, 2008, 11:24:57 AM »

Hey Frank,

Are you more-or-less along a straight line between Hartford and NYC? If so, couldn't you just use a bi-directional antenna and spare yourself the hassle of the rotor?

For that matter, if the stations you want all wind up on UHF after February, you could probably do a pair of UHF loops in a phased array and just switch line sections for the appropriate phase shift by latching relay. Phantom-power it off the coax. 1/2-second DC pulse on the coax to reverse direction.

Sounds like something that would be right up your alley.
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WA1GFZ
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« Reply #11 on: December 01, 2008, 11:58:54 AM »

No, I'm a few miles east of the mouth of the CT. river so N.Y. is SW and Hartford is NW. I didn't know the channels were changing?Huh I guess I'll hold off on an antenna for now. I have a nice rotor so not a big deal to turn the antenna. Just need to build a small tripod and bolt it in the attic. My problem is the whole house is shielded with foil over foam on 2 sides so the TV only works near a west side window. Once I get up in the attic it will be a nice groundplane.
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WB2YGF
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« Reply #12 on: December 01, 2008, 03:05:04 PM »

I didn't know the channels were changing?Huh I guess I'll hold off on an antenna for now.
Yes, some stations are moving their DTV transmissions to their original VHF slots except it's far less likely if their original allocation was on VHF Low. (Propagation and noise floor unfavorable.)

Looks like all the Hartford stations are staying on UHF and 7.1, 11.1, & 13.1 are going back to VHF in NYC.

In my area, I will have DTV on 6, 7, 8, 11, 12, & 13

Check out

http://www.w9wi.com/dtvch/dtvch.html
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WA1GFZ
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« Reply #13 on: December 01, 2008, 03:16:33 PM »

No point in having an antenna to cover the low end of VHF....more gain
I see 61 drops way down....someone must have had connections.
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Rob K2CU
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« Reply #14 on: December 01, 2008, 09:12:07 PM »

Frank,

You could experiment with the mini-circuits MAR 6  (20 dB broad band MMIC) and feed DC up the coax. a 24 ohm film resistor could match the input to 75 Ohms and use 24 Ohmer at the collector to match the 75 Ohm RG6 to bring the RF down. Feed DC with an RFC and DC blocking cap to input to TV. the MAR 6 gain more than makes up for the loss of the matching pads.

I have also observed the poor gain of some sets, mostly expecting cable inputs at fairly equal between channels and high levels. he same sets have shown poor dynamic range and often need a pad to prevent overload.
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WB2YGF
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« Reply #15 on: December 01, 2008, 10:47:47 PM »

I see 61 drops way down....someone must have had connections.
They had no choice but to move down.  52 through 69 will no longer be available for TV.  WNJB (New Jersey Public TV) is moving from 58 to 8.  Talk about connections!

A problem with DTV UHF is that output power is capped at 1000 kW so if more power is required to match the original VHF service contour, they are SOL unless they can increase HAAT or move back to VHF.
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W2VW
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« Reply #16 on: December 02, 2008, 08:01:38 AM »


Some of the information on this link is very outdated. It still shows NYC DTVs transmitting from the World Trade Center.

Some stations who are going back to their original analog frequency are transmitting low power on s really high UHF freq. Channel 61 is one of those.
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WA1GFZ
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« Reply #17 on: December 02, 2008, 08:46:13 AM »

Rob,
I have a jar of different MMIC amps. I was going to use something around 20 dB with a low noise figure. A wall wart off computer speakers should drive it fine. Also easy to run DC up the coax to the attic when the time comes.
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N3DRB The Derb
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« Reply #18 on: December 05, 2008, 12:23:31 PM »

Quote
I'd easily buy another Winegard, few dB noise figure.

my mast mounted winegard kicks ass.
http://www.winegarddirect.com/viewitem.asp?p=AP8800

75 miles from Baltimore and DC with the Blue Ridge (the one the Appalachian Trail is on top of) mountain in the way. I get 24 to 25 HD channels. Mast mounted preamp is the key. Anything Winegard makes is a winner. I would go with them all the way. If you could scare up some 75 Ω hardline that would really be a puller. RG-6 has lotsa loss @ 100 ft.

http://www.microwaves101.com/content/calculators.cfm
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