How does this powerless TV Amp work - Page 1
Forum section: electronics / general

author: touchh
author_rank: Contributor
timestamp: March 31, 2012, 11:27:58 pm
content: So, I'm browsing eBay for an amp for my Cable TV, and I come across this toy:http://www.ebay.com/itm/INLINE-AMPLIFIER-TV-CABLE-SATELLITE-SIGNAL-BOOSTER-HDTV-/130322190713?pt=LH_DefaultDomain_0&hash=item1e57ced179They've sold quite a few of them... I cant find anything online about them, and I've personally never seen an un-powered amp, let alone one claiming 30db gain in such a tiny package.Is this Chinese trash that is nothing but a placebo or how does this thing work?I'm almost tempted to buy one just to see whats in it.

author: Lightages
author_rank: Unknown
timestamp: March 31, 2012, 11:37:33 pm
content: If it does not have a power injector, and it does not have a power adapter, it does not work. Never mind that a 30db amplifier is not going to do anything to improve signal quality. They show a cleaner image with this installed. If there is noise in the original signal because it is in the noise floor then the amplifier will just amplify the noise too.It is useless garbage for the naive and the hopeful of miracles.

author: touchh
author_rank: Contributor
timestamp: March 31, 2012, 11:40:44 pm
content: That's exactly what I thought, I just cant believe they sold 4,000 of them.

author: kj5cn
author_rank: Contributor
timestamp: April 01, 2012, 12:08:35 am
content: It's not unpowered, if you read the description carefully: "...Powered through the existing coaxial run (no power cable is needed)...". Where that power is supposed to come from is another question. I'd expect a DC power injector box at the other end of the coax and a power adapter, but nothing like this is mentioned. Most likely the thing is a piece of garbage anyway, powered or not.

author: amspire
author_rank: Super Contributor
timestamp: April 01, 2012, 12:15:24 am
content: I suspect that some of the receiver boxes must provide their own DC power for a preamplifier - that would explain why this device does not need a plug-pack. You would be pretty disappointed adding this to a standard receiver that provides no DC.Receivers for satellite dishes have to provide power for the LNB downconverter on the dish, for example.

author: Lightages
author_rank: Unknown
timestamp: April 01, 2012, 05:01:16 am
content: From the ebay listing:"Delivers the best possible signal quality for:· All satellite systems including all free to air· Cable internet and TV· Broadcast TV or HDTV· Scanners· FM applications such as CB / radio"Obviously presented as a no power required device and not powered by any phantom or DC injected inline amp. Pure unadulterated BS.

author: Unknown
author_rank: Unknown
timestamp: April 01, 2012, 05:25:09 am
content: Quote from: amspire on April 01, 2012, 12:15:24 amI suspect you're right. Many receivers have a power over RF option in their menus.Quote from: Lightages on March 31, 2012, 11:37:33 pmSee above.Quote from: Lightages on March 31, 2012, 11:37:33 pmWithmost of the planet moving to digital TV, I doubt it cause you to see anything other than more dropouts.Quote from: Lightages on March 31, 2012, 11:37:33 pmNothing wrong with good masthead amplification, but this POS would never qualify as good anything.Quote from: touchh on March 31, 2012, 11:40:44 pmHell they've been selling indoor TV antennas for decades. There will always be a demand for false promises.

author: Mint.
author_rank: Frequent Contributor
timestamp: April 01, 2012, 05:29:15 am
content: Somebody buy it and post some photo's it doesn't cost too much.

author: amyk
author_rank: Super Contributor
timestamp: April 01, 2012, 12:03:04 pm
content: Quote from: amspire on April 01, 2012, 12:15:24 amYes, if you Google "inline amplifier" you'll find tons of sites selling these things, they're intended for satellite use and powered by the same supply as the LNB.Here's a real picture of the product with the same labeling, you can see the eBay seller has removed the word "LNB" from the input side.http://cdn.sulitstatic.com/images/2011/0824/122319292_12211979577de56cd818cef67b1a18174741418c68c0e1600.jpgSo in short: These are real inline amplifiers for satellite TV being sold as cure-alls for everything RF.

author: Fraser
author_rank: Super Contributor
timestamp: April 01, 2012, 12:55:25 pm
content: Awwww you are all being rottenTo be totally fair here.... there have been line powered wideband RF line amps around for decades in the satellite industry. They do work if used correctly. I used to be heavily into TVRO prior to the days of easy to use 'direct to home' mini dish stuff. I had a 1.2m Ku band Dish & LNB at the end of a long cable run at the bottom of my garden. Line amplifiers are a valuable asset on long cable runs whether you are using Satellite or lower frequency feeders. In the professional world you use slope gain corrected line amplifiers to compensate for the slope loss characteristics of coaxial cable. As the frequency gets higher, the more loss and so the more gain that is required to counter such losses on long cable runs. The advert correctly identifies this issue and the level compensation required when splitting a feeder cable two or more ways.Where this amplifier is amateur is in its claims to cure all problems as this simply isn't the case with RF feeds. For a start, if this is a lab grade flat response 30dB gain amplifier(it isn't but lets be generous) it would actually over amplify lower frequencies and likely cause all manner of overload issues at the receiver input. 30dB is one heck of a lot of gain for a simple line loss amplifier. More gain is not always a good idea and you need tight control over the gain slope and associated noise figure for the complete system.It should be stated that in many cases, such a simple non 'slope adjusted' amplifier MAY work on a very long coaxial cable run as receivers have become more tolerant of excess signal levels. The advertised amplifier is no different to a two stage Minicircuits MAR-6 MMIC gain block....great if used appropriatelyFor the price its cheap enough to try. A MAR-6 MMIC costs around $2 so to build this amp using two of them would cost you around $4 + PCB + connectors + Case. Mini-Circuits take one of their MMIC's mount it on a small PCB with some passive components and then charge a significant sum for the ready to install gain block....it isn't rocket science to use an MMIC so the cheap price shouldn't be an indicator that the amplifier is no good. If it turns out to contain a pair of Bipolar transistors on a crap PCB with similarly crap passive components, then that is another matterI have seen such coming out of China but they are usually limited to terrestrial TV and only 80-890 MHz bandwidth which isn't too demanding and analogue TV tuners were very tolerant devices.This isn't a professional device, but lets not call it crap either....unless that is , we buy one and prove it to be so

author: T4P
author_rank: Super Contributor
timestamp: April 01, 2012, 02:12:59 pm
content: Welcome to China . they sell loads of crap anyway .The biggest fail ever are those energy saving devices .

author: G7PSK
author_rank: Super Contributor
timestamp: April 01, 2012, 02:43:05 pm
content: All my TV's have 5 volt 60 ma written next to the coax socket in order to power mast head amplifier's. I think that it must be standard now here in the UK so perhaps that is the case in most other parts of the world, and these things are built with that in mind and expecting to find 5 volts on the coax line.