- #1
brainbaby
- 228
- 5
Can some one tell me how to generate following signal on LTspice XVII..
Thanks..
Thanks..
sophiecentaur said:If you want a representative spectrum of a coded TV picture (PAL or NTSC) plus sound, you need to take a suitable picture, amplitude a carrier and filter it with a vestigial sideband filter.
But it is not a spectrum diagram. It is a template.brainbaby said:Below is a more feasible diagram
Baluncore said:Why do you want that signal?
Can you attach the circuit you are wanting to test?
What change did you expect? FM demodulation is not an intuitive topic.brainbaby said:I made a circuit in LTspice XVII and tried to simulate it by changing the value of L4 at each attempt...but unfortunately I didn't found any noticeable change in the output of the circuit
The circuit under discussion comes from fig 22.17 of “Monochrome and Colour Television”. by R.R. Gulati. 2009. ISBN 8122416071. I would not expect the value of L4 to have a critical value in that wideband VHF TV tuner.brainbaby said:So I thought that it would be great if I test it out practically, so I made a circuit in LTspice XVII and tried to simulate it by changing the value of L4 at each attempt...but unfortunately I didn't found any noticeable change in the output of the circuit and that led me to think that may be its the input signal which is causing this dissimilarity as the text is strictly according to the input signal which is mentioned in post 3 of this thread...
Baluncore said:If you want to simulate general "band-pass coupling" you should be doing it over only one channel, not over the entire VHF band. You should also restrict your model to only the 10 components involved from the collector of Q1 = an AC 1 current source, to the base of Q2 = an output load resistor.
Not making things complex...the value of L2 above will govern the extent of band pass in the circuit...means the more the value of L2 the more will be the bandwidth i.e the more will be the band pass...sophiecentaur said:You really must be more forthcoming about what you actually want to do here. We are still pretty much totally in the dark.
Then just do an AC Analysis in LTSpice and look at the plots. Step the value of L2 to see the comparison of the passbands.brainbaby said:Not making things complex...the value of L2 above will govern the extent of band pass in the circuit...means the more the value of L2 the more will be the bandwidth i.e the more will be the band pass...
This is what I want to prove experimently using LT spice..
The dips and hollows represent less used parts of the spectrum that contain low energy, as such they are not important and so are irrelevant to the simulation. It is important to realize that the timing of NTSC or PAL analogue TV signals is very important, the spectrum usage is less critical.brainbaby said:I mean 50 to 70 MEG is ok for a frequency range of a VHF channel, but what should I do for rise and falls at 1.25,4,.5 Mhz...
Why would you even consider using a TV demodulator for receiving FM sound signals? You still haven't explained that for me. Just what is the application?brainbaby said:Also how close does .ac oct 1000 50MEG 72MEG corresponds to a single channel (as in post #1), I mean 50 to 70 MEG is ok for a frequency range of a VHF channel, but what should I do for rise and falls at 1.25,4,.5 Mhz...
The aim is I believe, not to build, but to study the double tuned band pass coupling network.sophiecentaur said:Why would you even consider using a TV demodulator for receiving FM sound signals? You still haven't explained that for me. Just what is the application?
He quotes (post 6) a previous thread of his involving a VHF tuner filter and he has not produced a frequency plot of that circuit's response. I'm a bit flummoxed by the mention of a "turret tuner". I never came across PAL on a VHF channel. That must surely be an historical spec (That quoted book is fairly recent, though). A proper superhet design would be suitable for all frequencies (VHF UHF ) and not a clunk clunk control with only a few channels. CATV may be a different environment. In the UK, it's all digital, afaik.Baluncore said:The aim is I believe, not to build, but to study the double tuned band pass coupling network.
The circuit provided is for a VHF TV turret tuner that includes FM sound.
@sophiecentaur; where does @brainbaby specify only FM sound?
Absolutely true.Baluncore said:The aim is I believe, not to build, but to study the double tuned band pass coupling network.
Baluncore said:The circuit provided is for a VHF TV turret tuner that includes FM sound.
sophiecentaur said:@brainbaby: you have really confused me now. The thread you reference is about an FM sound circuit. Why would you need to include the whole TV signal. If you want to get the FM sound carrier from the TV (i.f.) signal then the most popular way is to use 'inter carrier demodulation' which puts the whole TV signal through a non linearity and filters out the 5.5MHz component (difference between sound and vision carriers).
sophiecentaur said:If that amplifier has to deal with the composite signal, it would be much more important to get amplitude and group delay at the colour subcarrier.
sophiecentaur said:But the whole scenario here has not been specified enough for a proper answer
No really. The VSB filtering is before the AM demod, in the IF filtering.brainbaby said:It seems that you are more focussed in discussing the later part of the whole TV reciever circuit, which is the demodulater (post video detector stage)
If it's a monochrome circuit then why are you choosing a spectrum template that refers to a colour channel? I only know about monochrome tv in the context of the old 405 (uk) line system. Is there a monochrome TV service anywhere in the world, these days? I used the terms NTSC and PAL right at the top of the thread but no one picked me up. Which TV system letter are we discussing? I cannot find any mono systems that are current. This is even more confusing, now. Where is your interest in that niche in TV?brainbaby said:Its a monochrome circuit.
Now all this makes total sense but has nothing to do with the test signal you were wanting in the OP.brainbaby said:Now here the resistance R is common(shared) between two circuit loops and by manipulating its value we can affect the magnitude of current flowing in loop 2. The same goes with inductances as well (like L1,L2,L3)..as manipulating value of L2 will effect transfer in the rest next of the circuit. This is known as shared impedance coupling and that exactly was what I tried proving using a simulation in LT spice.
The references you need are here.brainbaby said:I am trying to frame out certain values of frequencies along with amplitude for different values of Lm…but the problem is that for this I need a relation aka formula which establish a relation between these three variables i.e Lm , fx and amplitude.
So can I have it??
LTSpice XVII is a simulation software used for designing and analyzing electronic circuits. It can also be used to generate TV spectrum by simulating the behavior of a TV system and producing the corresponding frequency spectrum.
Yes, LTSpice XVII uses advanced algorithms and models to accurately simulate the behavior of a TV system and generate the corresponding frequency spectrum. However, the accuracy of the results also depends on the accuracy of the circuit model and parameters used in the simulation.
The TV spectrum generated by LTSpice XVII can be affected by various factors such as the circuit model used, the frequency range and resolution selected, and the simulation settings. It is important to carefully select these parameters to ensure accurate results.
Yes, LTSpice XVII can be used to analyze and optimize TV systems by simulating the behavior of different circuit designs and analyzing the corresponding frequency spectrum. This allows for the evaluation and improvement of various parameters such as signal quality and bandwidth.
LTSpice XVII has the capability to generate TV spectrum, but it is important to note that it is a simulation software and may not account for all real-world factors. Therefore, the results should be used as a guide and verified with actual measurements for accurate analysis and design of TV systems.