Mains interference: Digital TV problems

On Mon, 12 Jun 2006 17:55:09 -0500, "hob" Gave us:

Straight modulated SCPC, perhaps... But there are NO digital transmissions that are straight modulated anymore. (likely for nearly

40 years now).

Ever heard of PSK? How about QAM?

Get a clue, "top clipper boy".

On Mon, 12 Jun 2006 18:37:57 -0500, "hob" Gave us:

Even the tiny feeds up to my headphones are coax.

Co... axial. That's all that is required. It is a physical structure, and YES, the audio uses the shield of the coax as a return.

It is typically referred to as a completed circuit.

It does not add bits. But it will cause errors in the bits that exist.

In most systems the data is framed, and adding even a single bit would result in a loss of framing. At that point all data is lost until framing is re-acquired. Hence, rather than a single bit error, there would be a huge loss of all data.

Gasping would be correct. I am utterly aghast at your responses.

Perhaps there are systems where that is true, but that is *not* a necessary part of a digital system. For example, in a T1 Carrier system, where is *anything* based on rise time?

Even for a typical RS-232 port on a PC, rise time has nothing to do with signal detection.

If your system is sensitive to rise time, it *is* going to be sensitive to phase hits.

You are stating that a "real digital signal" has pulses. That is not necessarily true.

You are the one who said "well below the level of the pulses". That would, for example, exclude phase noise. Which is why I pointed out that your definition of a "real digital signal" is invalid.

Well, which do you want to talk about, a tuner or a digital amplifier? The input stage in a tuner is *not* a digital amplifier.

The input amplifier of the tuner is analog. The transmission medium is analog. The modulation scheme is digital, not the input signal.

I haven't said a thing about RCA audio cables, but certainly most cables sold with RCS plugs on both ends are in fact coaxial cables, simply because RCA connectors were specifically designed for coaxial cable.

And in fact insertion loss of a device *is* total loss through the device.

Insertion loss:

1. The loss resulting from the insertion of a device in a transmission line, expressed as the reciprocal of the ratio of the signal power delivered to that part of the line following the device to the signal power delivered to that same part before insertion. Note: Insertion loss is usually expressed in dB.

Insertion Loss:

1. The loss resulting from the insertion of a device in a transmission line, expressed as the reciprocal of the ratio of the signal power delivered to that part of the line following the device to the signal power delivered to that same part before insertion. Note: Insertion loss is usually expressed in dB.

In fact, that is true. See the definition of Insertion Loss.

A "parallel line in series into a line" is something that I don't understand. Can you explain what that is supposed to be?

You'll note that I've stated there is a hybrid loss in these splitters, usually 0.5 dB, but perhaps as high as 1 dB. That is the lack of "100% efficient transfer". The other 3 dB in the insertion loss is the fact that the power is split two ways, each will see a 3 dB reduction in power.

Wrong. If there was a 6 dB drop in strength at a port, that would be a 6 dB insertion loss. In fact, as noted, the insertion loss is 3.5 dB, and in fact if you do have correctly match impedances, the output at each of the two ports will be

3.5 dB less than the input signal on a two-way splitter.

You have demonstrated that to be the case.

Giggle snort laugh cough. Who is it that doesn't understand what?

See what it says there? Each port will have a signal that is "approximately 3.5 dB (4.0 dB)" lower than the input signal.

*That* is insertion loss.

And the signal at the output ports is 3.5 dB less than the signal at the input port. *That* is insertion loss.

I see that this went totally over your head, and you had no response. The point, since you may have missed it, is that you totally misread the material you cited.

A 2-way splitter is merely a 4 port hybrid with one port terminated. The terminated port is isolated from the input port, there is *no* 3 dB loss in the input signal associated with that resistor.

You mean, I assume, patch cords using "RCA Plugs"? They are virtually

*all* made up with coaxial cables. That is because the plug is designed specifically for coaxial cable. (It was originally called a "Phone Plug", because RCA used it for the coaxial connection to a phonograph arm.)

Okay. That is a *physical* description.

That is an electrical description of a transmission line. It happens to be the way that transmission works when the physical device is a "coaxial cable".

Hence, they fit even *your* description of a coaxial cable.

So? It is still physically a coaxial cable.

Coax is very commonly used for audio; primarily because it is a very effective transmission line. In addition to fools buying, smart folks do to! (RCA, for example, used coax for audio and tha is how we happen to have a coaxial connector called a "RCA Plug"!)

Sure.

"TimPerry" wrote in news:9vedndrrue5uChbZnZ2dnUVZ snipped-for-privacy@adelphia.com:

(snip)

I've just tried this, and it works an absolute treat!! The Lion's share of the interference has gone. Such a simple thing - I'm not even going to try to pretend to understand the physics, I'll just apply Arthur C. Clarke's definition of "Magic"!

Thanks very very much.

Quadruple Amplitude Modulation still has to pick signal out of the background noise in order to use it.

You could call it RFU and still have to pull signal out of the background.

Get a clue, "no amp needed in my world boy"

Its what you drip on your keyboard. Four times.

A way to cram more shit into the pipe.

And what errors will you see on the bits that pass out of the input processor? And from where did those errors come?

In digital "amplifiers", a signal is "heard" at the input, and if it has the necessary parameters, it triggers the "amplifier". The input is isolated from the output, because the "amplifier" generates a totally new pulse (unit, not Legrange/Leplace pulse) unrelated to the old pulse except in it's time occurence. I trigger the "repeater" and I can get out a pulse larger or smaller, longer or shorter, phase shifted or not, delayed whatever I like - but NOT the same pulse that went in. That creating of the new signal to work with in the circuit is the reason digital processing is more reliable than analog rpocessing - but it is still garbage in - garbage out -relying on readable input.

So exactly what are the input-derived output errors that occur in a digital "amplifier", if not added or dropped bits?

ALL digital amplifiers discriminate on risetime - it is an inherent property of amplifiers, both analog, digital, and hybrid. Look at it this way:

- A fast rise time repeated is what makes a high frequency sinusoid.

- Think of a pulse (not the LeGrange/LePlace pulse, but rather unit function, that shows as a pulse of definite duration as seen on the scope) as having part of a sinusoid on its leading edge.

- The input system will only see whaty is in its frequency/rise time range.

As illustrations: an audio amplifier cannot reproduce RF because it cannot follow the rise time in its circuitry; Filters will not reproduce fast rise time signals. Those have inherent rise time discrimnators.

A digital amplifier (e.g., the chip input sector) discriminates against fast rise times by virtue of its physical construction (architecture), physical arrangement (components), and basic design type (e.g., amp-amp vs parametric vs etc.). A rise time of a digital pulse corresponding to 100 G sinusoid will not be repeated by an amplifier designed for a digital amplifer designed for the rise time of a 1M amplifier.

Those are limitations of ALL amplifiers - rise time discrimination.

A completed circuit on a pair of wires does not make a coaxial cable - co-axial conductors of unidirectional transmission makes a coaxial cable.

Wrong.

"Unidirectional transmission" has nothing to do with defining a coaxial cable. A coaxial cable is a *physical* description, it has

*nothing* to do with what kind of signal it might have on it.

A coaxial cable that has a DC voltage on it is still just a coaxial cable. Cut it out of that circuit and splice it into a circuit with bidirectional audio signals, and it is *still* just a coaxial cable. Plug it into a circuit with microwave RF on it... and it is *still* just a coaxial cable.

Ground the inner conductor and the outer conductor at to the same point, and it will still be nothing more or less than a coaxial cable.

Yes - the ATIS committee definition -

"The loss resulting from the insertion of a device in a transmission line..."

That is NOT the comparison of what goes in to the input port of an inserted device to what goes out a given port of a multi-port inserted device - rather, it is the LOSS caused by the device itself - loss resulting JUST because of inserting the device into the line: Insertion loss.

Carefully read the definition - the number means -> "reciprocal of the ratio of..."

"...the signal power delivered to that part of the line following the device" (the sum of ALL output ports' signal power combined - not just ONE port's power out -"THE" line, not "A" line)

"to the signal power delivered to that same part before insertion" (what was there before it was inserted - NOT what goes into a port AFTER it is inserted, but what was there BEFORE it was even inserted.)

i.e,, the ratio of what was there before the device was put into the line, to the total of what is coming out of the device after you put the device into the line.

The specifics of the ATIS definition account for impedance mismatch on the input causing a loss of signal (vs no mismatch), it accounts for mismatches on the output, and it accounts for inherent losses in the device - "insertion loss" is the sum of what comes out of all ports vs what was there before the device was put into the line.

Thus the insertion loss of a two way splitter of 3.5 db is realistic, given that the insertion loss has to be at least 3 db theoretically and there is a need to broadband the output across the device's quoted bandwidth.

There are a number of websites that do not repeat the ATIS defintion nor understand it - they paraphrase it as if it it a power in to power out ratio of the device. That is incorrect.

(FWIW, it is my understanding that the actual loss, input to any output, of passive devices depends on "seen impedance" and frequency of signal. This can be seen as valid by remembering how one broadbands an output - by increasing impedance mismatch to increase frequency pass - and by how to transfer maximum power - by impedance matching which decreases frequency pass.

If the device is a 10 db limiter, it has an insertion loss.

If the device is a 10 db amplifer, it has an insertion loss.

If the device is a 2 way splitter, it has an insertion loss.

Insertion loss is NOT the overall signal change created by the device - it is the price paid in signal for insertion into the line.

The errors will be symbols with the wrong values. They come from any part of the circuit. For example it might be due to low input SNR, it might be due to faulty components, or whatever.

(I suppose it might be fun here to inject the fact that not all digital systems actually work with "bits". A bit is a *binary* information block, and many digital systems are m-ary, where "m" is greater than 2. No actual bits, just symbols, some with values larger than 2.)

You appear to think that "digital" means it is some kind of a binary voltage pulse. Something like you'd see for TTL, RS-232, T1, where a "pulse" of the appropriate amplitude is a 1 or a 0 value.

First, that is *not* what defines "digital", and secondly not a one of those is necessarily edge triggered vs. level triggered. Which is to say that rise time is absolutely insignificant for some applications.

T1 is an example. Just where do you claim the signal for a T1 carrier system is sensitive to rise time?

Yes, the advantage of digital transmission systems is the fact that a new signal is regenerated at each node.

As I previously noted, noise is cumulative in analog systems, and errors are cumulative in digital systems.

*Errored* bits! No bits are added. No bits are dropped. They just have the *wrong* *value*. A symbol that was supposed to have the value 64 ends up with a value of 2.

Wrong. I just gave you an example, and you will *not* find

*any* place in a T1 digital carrier system where the signal is rise time dependent for correct decoding.

In fact, the rise time will be *very* significantly changed between the transmitter's output and a receiver's input, depending on the length of cable. Hence the rise times expected if the cable is 10 feet long are very short, and voltage pulses look like square waves, but if there is a mile of cable the voltage pulses are nothing close to a square wave and have very long rise times (a sine wave!).

Sine waves, at any given frequency, have significantly slow rise times compared to, for example, a square wave pulse at the same frequency.

That's a wonderful set of words. Do you know what you said? Was it supposed to means something specific? I particularly liked the "rather unit function" group! But "a sinusoid on its leading edge" ain't bad either.

I've got a program that generates nonsense phrases from real words somewhere, but it doesn't do that good.

I've seen *many* amplifiers used for audio that could and would reproduce RF.

Regardless, all you are saying is that amplitude distortion is inherent in electronic circuitry. That is true, but digital amplifiers to not necessarily make any inherent use of that characteristic; in fact they often go to extremes to avoid it! (Which is to say, digital is commonly very broadband... :-)

What is a "100 G sinusoid"? What is a "1M amplifier"?

I take it that was meant to be some sort of frequency specification; and if so you are *wrong*. It might not be able to respond to it, but in fact it might. Excess bandwidth is not inherently detrimental...

But it is not part of the functional design for digital amplifiers.

No response?

No response? I clearly said that you were making false statements, because you don't even realize that the input to the tuner is analog, not digital.

No response? What's the matter, did you suddenly realize how far off base you were with those statements?

The definition of "Insertion loss" negates everything you've said about it.

not if it is not carrying signal using both conductors

Yes it is. Can't you read?

That's right... the difference between what goes in and what comes out.

The input impedance will be that of the terminating resistor, while the two output ports will each exhibit an impedance which depends on the impedance terminating the other. Hence if the resistor is 52 ohms, the input impedance will also be 52 ohms, and if a 52 ohm resistor is used as a load for Port B, then Port A will match 52 ohms.

There is no impedance mismatch...

Nowhere can you find a definition which says that.

The output of a two way splitter, if the input is 0 dBm, will be

-3.5 dBm on both ports if they ar both terminated in a proper load.

(BTW, when are you going to figure out that the term is "dB", not "db"?)

You don't understand it, and are not describing it correctly. You also clearly have never measure the insertion loss of a hybrid.

"Seen impedance" ???

Impedance matching does not decrease frequency pass, nor does increasing impedance mismatch increase it.

What is a "10 db limiter"?

Yes, and the value is -10 dB.

Yes, and it is going to be very close to 3.5 dB.

The price paid in signal for insertion into the line *is* the "overall signal change created by the devic".

Well, can you explain what that verbiage is supposed to mean?

And that does *not* agree with the foolishness that you have described above, does it!

Coaxial cable is coaxial cable, it makes *no* difference what signal, or even if there is a signal, is being carried.

Coaxial cable can be used to tie up your dog, and it is *still* coaxial cable.

On Wed, 14 Jun 2006 09:53:35 -0500, "hob" Gave us:

Huh?

It is Quadrature Amplitude Modulation. Do you know anything about noise immunity?

Do you know why satellite receiver dishes are no longer 8 and 16 foot diameter behemoths?

You're an idiot. MY HDTV receiver HAS an amp on the antenna.

On Wed, 14 Jun 2006 09:55:47 -0500, "hob" Gave us:

Damn! You got one right!