Signal Amplifiers (Amps, Preamps, Distro Amps) - Page 4 - Canadian TV, Computing and Home Theatre Forums

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post #46 of 4296 (permalink) Old 2005-11-07, 01:53 PM
 
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Actually I just got off the phone with Sal's TV technician... and he's convinced that downstream from the preamp there should be no breaks in the cable (ie no spliters, grounds-blocks or joiners). To a certain extent I understand the splitters ... but his explanation that the injected 27V (ac/dc??) is 'arcing' to the coax shield seems unreasonable to me. And yes... I did mention that both Channel Master and national electric code are looking for the shield on the coax to be grounded. So ... he's convinced that it's the cabling. I can't imagine the setup working with the SAME cabling (with this supposed path to ground) with 500+ Mhz signals on there, with this pre-existing low voltage low frequency path to ground. Is it me or is he not making sense?
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post #47 of 4296 (permalink) Old 2005-11-07, 01:59 PM Thread Starter
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gordee78, some time ago I asked in the OTA Forum if anyone in the GTA was needing a preamp to get the stations they want, and I was told that nobody would need one in the City of Toronto for local and Buffalo stations. Maybe you need to talk to a different antenna guy to try some things out. I say that because I could go up on my roof right now here in the Vancouver area and easily overload my system by simply putting in one of my preamps, which is what happened in your case.
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post #48 of 4296 (permalink) Old 2005-11-07, 02:40 PM
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gordee78 on my setup the cable from the preamp goes into a ground block and from there into the power supply.

I have no problems with the setup using a preamp.

CM4228/9521/7775;F.RmJvc70FH96/8300HDPvr/Dish 612;B.Rm LC52LE810UN/8642HD;Study LG50PK550/Xbox360;
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post #49 of 4296 (permalink) Old 2005-11-07, 04:49 PM
 
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Quote:
Originally Posted by stampeder
gordee78, some time ago I asked in the OTA Forum if anyone in the GTA was needing a preamp to get the stations they want, and I was told that nobody would need one in the City of Toronto for local and Buffalo stations. Maybe you need to talk to a different antenna guy to try some things out. I say that because I could go up on my roof right now here in the Vancouver area and easily overload my system by simply putting in one of my preamps, which is what happened in your case.
Agreed -- it's quite clear that although he's an experienced tech, there's some lack of fundamentals. I noticed it when he referred to an oscilloscope as an 'electronmicroscope' to 'see the arcing of the 27Volts' ... 'AND it's AC' ... all three statements have seriously made me question his advice on the preamp.
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post #50 of 4296 (permalink) Old 2005-11-07, 04:51 PM Thread Starter
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Perhaps you should invite the fellow to come here and join DHC! I think his employer would appreciate him doing that too. In the meantime you have some good resources here about GTA.
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post #51 of 4296 (permalink) Old 2006-02-04, 01:26 PM
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Pre-Amp Problem

I just bought a Winegard Antenna Pre-Amp and i'm very disappointed in the results. I'm asking if anyone has experienced similar problems?
The Pre-amp is Model# AP-8780, its rated 28dB @ UHF & 16dB VHF. I have a 4228 & 4221 combined.
Before I put the pre-amp up on the tower I thought I’d test it here in my living room.
I have the signal split to go to both tuners, ATSC & NTSC.
With the amp on, I get less signal on digital and less signal & more noise on Analog.
Maybe I have too much Signal? Would a tuner automatically attenuate to protect itself? I tried a 6dB attenuator which made no difference with the amp on, but un-plugged the power supply and lost signal completely.
The reason I need the amp is I wanted to split the signal to go 6 different places.
Any input would be appreciated.
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post #52 of 4296 (permalink) Old 2006-02-04, 01:48 PM
 
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I have the Winegard AP4700 which is a UHF only pre-amp. (All the HD OTA in my area are UHF). This is on my mast with the CM4228. The excellent part about this pre-amp is the overload protection.

I found that when I used the amp in the house, it didn't work, but installed it on the mast, then it worked. It must want to see a length of cable as a load.

Also, too much signal will give you a blank output, same as too little signal.
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post #53 of 4296 (permalink) Old 2006-02-04, 09:11 PM
 
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Tom F1 seems like your pre amps not working.Is it connected correctly:antenna to preamp to power supply to tv.If overload is the problem than put the attenuator before the preamp to see if its the preamp overloading.If your within 30km of a tower it may overload.

Attic CM 4248 at Buffalo,M4 at Buffalo.VHF yagis at Toronto .
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post #54 of 4296 (permalink) Old 2006-02-20, 12:07 PM
 
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Preamp advice needed

Recently I switched from a CM4248 yagi to the 8 bay bowtie for improved UHF signal capture. IN my opinion it stands to reason because of the physical nature of the design. I think it has worked well but I need some advice on the pre-amp. Several years ago I purchased a Wineguard Vaulter Plus model with 37db gain on UHF. The noise factor is high though as it rates at 4.5. Since I already had it, why not use it right? My results could use improvement because the reliability of DTV signals is very spotty. Daytime will mean I lose everything unless it is bitter cold, then I'm great. I am considering the CM7777 that seems to be popular but I am concerned that the gain is significantly lower at 20db. I remember reading in an earlier post that digital signals don't do well above 20db gain if at all.
Your comments on my line of thinking would be very much appreciated.
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post #55 of 4296 (permalink) Old 2006-02-20, 12:31 PM
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Scuba my advise is that you dont really need to use a preamp unless you are encountering a loss from long cable runs more than 60 to 70' or from splitting the signal a few times with long cable runs.

Where are you located in the Toronto GTA area ?

37db in my mind on most installs would be way too much gain/signal and you would end up with many channels pilexating because there is too much gain going into the receiver.

Even then I have found that a CM7777 or 7775 at times can have too much gain.

I myself have found this since I get a strong and clear signal from my antenna setup and have a short cable run. I only used a pre amp because I was going to drive several hdtv tuners.

With my setup I found that I had to add splitters or attenuators before each receiver. Some atsc tuners can handle overload better and some are more sensitive.

With most installs I would recommend the lower power preamp like a Winegard AP4700 at 19db. There is enough gain to compensate for long cable runs 100' and splitting the signal at the same time.

If you really want to use your old preamp or a high power preamp, then I would suggest you buy a few attenuators and have them handy incase you find that a few channels are pilexating. Just keep adding the attenuators in series till that channel becomes clear and stable.

Buy the correct ones rated to cover the full frequency that UHF needs atleat 50-850mhz.

I also sell and stock attenuators that covers 5-1000mhz in different db.

Good luck.

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post #56 of 4296 (permalink) Old 2006-02-20, 06:41 PM
 
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Scuba I find the long Yagi gives more reliable reception because of their narrower reception lobe which reduces multipath reception.The 37db pre-amp may overload if your closer than 30km to transmitter tower.

Attic CM 4248 at Buffalo,M4 at Buffalo.VHF yagis at Toronto .
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post #57 of 4296 (permalink) Old 2006-02-21, 02:29 AM Thread Starter
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Scuba, the Vaulter Plus was a Blonder Tongue product, not a Winegard, but maybe Winegard resold it or something. I've read comments in the past on other OTA sites that the Vaulter Plus was a good product but that the CM7777 is better. Do a Google and you'll see that sellers are listing the Vaulter Plus as discontinued. I think BT changed over to their Galaxy line and dropped the Vaulters.

The Vaulter Plus put out over 30dB on VHF and almost 40dB on UHF. Those figures are scary, especially given the old-style electronics involved, so I don't think you want to mess around with that much energy without putting attenuators inline downstream at first. Maybe just avoid it and sell the preamp to someone in a desperate deepest fringe scenario...

Given the great pair that a CM4228 makes with a CM7777, I think you are right to go with those. Scuba, let us know your location so that we can understand your results better.
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post #58 of 4296 (permalink) Old 2006-02-25, 09:53 AM
 
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Pre-amps damaging OTA tuner front end?

Hi stampder,

On 14th February you suggested that too much signal into a pre-amp could fry the front end of a tuner.

I was in the TV design industry in the UK and we never came across a problem with tuner damage from pre-amp signal strength.

A pre-amp runs on low voltage and cannot put out enough energy to damage a tuner front end. Added to which, is the fact that front ends in US sets in particular can handle high signal levels due to them often being close to transmitters. Seattle is a good example of this.

The worst I would expect from a high signal input is overload of the pre-amp and/or tuner front end.

However, if the pre-amp design is poor and goes into oscillation under high signals, then I agree it might be possible to damage the tuner front end.

Rick Dude
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post #59 of 4296 (permalink) Old 2006-02-25, 03:55 PM Thread Starter
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Hi Rick, that's great information. My concerns about preamp overload should have been expressed more widely in scope since I also worry about any other connected gear such as FM tuners, etc., but I need to pass along that with 2 recent ATSC tuner purchases (one set top box and a pc card from different companies) they both adamantly warned about damage to the units from overly high signal input. Neither of them specified whether this was more specifically a signal strength, line voltage, or other issue, so I'll make some inquiries. My LG ATSC Tuner came with a direct warning to use attenuators at first, so I infer from that warning that it is about raw dB signal strength. Anyone have some thoughts or info on this?
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post #60 of 4296 (permalink) Old 2006-02-25, 06:30 PM
 
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I had some signal overload issues with my LG 3410a tuner. I had to end up adding an additional splitter before the tuner to prevent channel breakup. At first, I thought the channel breakup was due to low signal levels. I went to my basement and disconnected the splitter only to experience more breakup. At this point I decided to add the extra splitter and everything has been fine.

The strange thing is my Samsung SIR-T151 never had any issues with strong signals. I used to feed a direct connection straight into the Sammy and he wouldn't even blink. Currently, I'm feeding -7dB into my LG.
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