TheBroker Posted March 6, 2007 Report Share Posted March 6, 2007 Hello, I saw a project here named "TV Signal Amplifier source: smartkit" and it says it will amplify weak tv signal. I was assuming that the purpose of this amplifier is to boost TV signal so that you can watch now an improved reception, correct? My question: If you amplify the weak TV signal, you will also amplify the noise or raster effect of this weak TV signal. So overall, you still have a very bad reception ?? It does not improve anything. Please clarify... Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 6, 2007 Report Share Posted March 6, 2007 If you live anywhere near a TV station then this very simple circuit will be overloaded and won't amplify another weaker station. It is not tuned like the input of your TV.If you live away from any TV stations then your TV will be operating at its max gain and this very simple circuit won't do anything except amplify its own noise.If there is only a single TV station that is weak, then this very simple circuit could amplify it at the antenna, to make up for the loss in a long cable from the antenna on the nearby mountain to your TV. Then it is a useful amplifier. Quote Link to comment Share on other sites More sharing options...
TheBroker Posted March 6, 2007 Author Report Share Posted March 6, 2007 Hi, thanks for the reply. So this simple signal amplifier is only practical to use if you have one or two tv channels that are weak? The reason of my inquiry because I have a set-top-box that converts analog tv signal to digital then it is fed to my tv's A/V. The problem is, I have 2 tv channles that are very weak and my set-top-box cannot convert it to digital anymore and it will just show a message "No Signal" for those 2 weak channels. So I am finding a way to boost the tv signal before it is fed to my set-top-box. Any alternative solution for this? Or the best thing is really to boost the signal before it's fed to my STB. Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 6, 2007 Report Share Posted March 6, 2007 It is complicated.You must tune in the weak signals before the amplifier to avoid other stronger stations from overloading the amplifier. The tuned circuits might not be sharp enough.Then you must mix the amplified signal into the STB somehow. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 7, 2007 Report Share Posted March 7, 2007 I wanted to convert my standard rabbit ear antenna into an amplifying antenna. Looking at the circuit, it's all impedance matching. I think trying to add an opamp would just screw things up. Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 7, 2007 Report Share Posted March 7, 2007 Opamps don't work at VHF and UHF. A 741 opamp has a voltage gain of 200,000 at DC but no voltage gain above 1MHz and its output can't swing above 1MHz anyway.You need a high frequency RF amplifier if all TV signals are very weak. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 9, 2007 Report Share Posted March 9, 2007 Correct me if I'm wrong, but reducing gain increases bandwith. A 741 can be operated up to about 1Mhz at very low gain. I would have opted for a high frequency opamp in this case, which they do make real high frequency opamps. Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 9, 2007 Report Share Posted March 9, 2007 Look at the datasheet for a 741 opamp.With 100% negative feedback it has no gain because its output level is the same as its input level up to about 9kHz. Then at higher frequencies its max output level drops because of "slew-rate-limiting" where the output becomes a triangle-wave and it can't "slew" as fast as its input so its amplitude becomes less at higher frequencies. At 1MHz and higher its output level is zero. It is old fashioned.For audio, I use TL07x opamps that have full output level up to 100kHz. They are inexpensive, come as single, dual and quad, have low distortion and low noise. Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted March 11, 2007 Report Share Posted March 11, 2007 hi audioguru!Can you tell me what will hapen if we try to Frequency modulate both sound and picture in a TV unlike AM for video .I was just kind of experimenting with this ...have u ever tried this in past? Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 11, 2007 Report Share Posted March 11, 2007 The video detector in a TV is a diode like in an old AM radio. It doesn't respond to frequency changes produced by FM.It would be difficult to make a TV transmitter and TV receiver with the video FM modulated because the bandwidth is so wide. Quote Link to comment Share on other sites More sharing options...
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