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-   -   A long winded blog post re. amplifiers (http://forum.tvfool.com/showthread.php?t=1514)

GroundUrMast 31-Mar-2011 9:26 PM

A long winded blog post re. amplifiers
 
1 Attachment(s)
Feel free to suggest edits to the attached. Thanks.

The condensed version of this is: Choosing an antenna or amplifier will effect two common factors: signal strength and signal to noise ratio. An antenna can offer an improvement of both factors. An amplifier can only improve one at the cost of the other.

And maybe an answer to the question, "How big a pump do I need to get water out of a dry hole?"

GroundUrMast 14-May-2011 2:59 AM

What is the difference between Signal Strength and Signal Quality?
 
Generally, Signal Strength is simply a measure of the power of a signal. If the measurement is expressed in watts or some variant thereof, the measurement implies the the amount of heat that would be dissipated if all of the energy was terminated in a purely resistive load. Signal Strength does not measure the integrity of information that may or may not have been encoded or modulated into a radio wave. In the case of OTA DTV, power in units of dBm is common. Not as common, but still used are units of milli-volts and dBmV, and because the system impedance is nearly universally 75Ω, a direct conversion to units of power can be made using Ohm's and Watt's laws. http://en.wikipedia.org/wiki/Decibel

Signal Quality generally refers to some sort of measurement that describes how well the measured signal resembles the original signal transmitted, or, how likely the original information may be decoded or demodulated without error. A signal can be altered, distorted or interfered with in many ways, therefor, the quality of a signal can be measured in many ways. Signal to noise ratio is a measure of how much noise and/or interfering signal has been added to the desired signal. In the case of digital signals, error rate is often used as a measure of quality.

An analogy exists in the audio world. As you are sitting at a stop light, listening to the stereo system in the car behind you, you are likely quite aware of how loud the sound is. Just because it's loud enough for you to hear, does not mean you can understand lyrics or even identify the song being played (perhaps the rattling fender sound is a source of interference). You could measure the power of the audio signal with a sound level meter, which may be helpful to understand whether you are at risk of damage to your hearing, but that simple 'sound strength' measurement will not quantify the quality of the audio. Measuring the ratio of desired signal verses noise plus interfering signals is a more complex measurement that would be an example of how to quantify quality.

This link http://www.guitarkitbuilder.com/cont...d-oscilloscope offers a visual of audio distortion. In the case of the guitar, distortion is desirable at times, if it can be controlled and used artistically. When trying to send information error free, distortion would not be desired or helpful.

ChrisAntennahead 9-Jan-2012 7:53 PM

Question: Can error rate also cause the signal meter to go up or down?

GroundUrMast 9-Jan-2012 9:08 PM

Quote:

Originally Posted by ChrisAntennahead (Post 19117)
Question: Can error rate also cause the signal meter to go up or down?

Short answer, yes.

I've yet to see any DTV manufacturers disclose the exact method used to indicate signal "strength" or "quality". (Which term used does not seem to be based on the precise definition of the word used on the TV display.)

That said, I would venture to guess that most DTV signal meters use digital error rate and possibly RF stage AGC level in some combination with digital error rate.

Sony is an exception that also provides reporting of signal to noise ratio, but how they measure SNR is not on their home page.

ChrisAntennahead 9-Jan-2012 9:14 PM

Quote:

Originally Posted by GroundUrMast (Post 19125)
Short answer, yes.

I've yet to see any DTV manufacturers disclose the exact method used to indicate signal "strength" or "quality". (Which term used does not seem to be based on the precise definition of the word used on the TV display.)

That said, I would venture to guess that most DTV signal meters use digital error rate and possibly RF stage AGC level in some combination with digital error rate.

Sony is an exception that also provides reporting of signal to noise ratio, but how they measure SNR is not on their home page.

Glad to know that. <sighhhh> It seems like this whole digital transition was just another way of government just trying to make things "fun" for us. Analog was fine - if you could deal with varying degrees of snow versus the absolute terms of digital ALL or NONE.

Oh well. "progress"

GroundUrMast 10-Jan-2012 5:24 AM

Quote:

Originally Posted by ChrisAntennahead (Post 19126)
Glad to know that. <sighhhh> It seems like this whole digital transition was just another way of government just trying to make things "fun" for us. Analog was fine - if you could deal with varying degrees of snow versus the absolute terms of digital ALL or NONE.

Oh well. "progress"

I have moments where I'm thinking similar thoughts. But I also like being able to watch 720p and 1080i content. Access to the expanded range of programing on the sub-channels is nice. And I really like being able to record direct to hard-disk.

mtownsend 10-Jan-2012 4:38 PM

I like to think of it as the evolution of more tech-savvy consumers.

Even in the days of analog TV, things like SNR, noise figure, power levels, amp overload, gain, and adjacent channel rejection were very important, but people were not so well equipped to interpret the technical specs or make informed decisions based on them.

Today, we have an amazing repository of information and tools at our fingertips, thanks to the internet. Now we can base our purchasing decisions on real facts and hard data instead of relying on marketing- or emotion-driven impulses. The sharing of information has resulted in tremendous growth of our collective depth and breadth of knowledge.

A lot of the technology is actually still the same as before, but our ability and confidence in understanding the underlying technology has gone up significantly.

GroundUrMast 25-Jan-2012 3:22 AM

There's always someone who can say it better than I can
 
There's a bit of specific product promotion embedded in the following Application Note, however, there's plenty of sound technical information that applies to OTA amplifiers in general.

http://www.emceecom.com/Documents/EM...e%20062207.pdf


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