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use of increased transmitter power to increase converage

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PG1995

Active Member
Hi

Are cost and equipment failure the only reasons for not using too much power for a signal transmission in wired communication? By the way, what's that 'high-voltage rupture'? Increased signal power can also make the use of amplifiers etc. needless.

Note that broadcast transmitter is made up of radio transmitter equipment plus antenna.

Likewise, is this possible to use increased transmitter power to achieve greater coverage? This will make the use of repeaters etc. unnecessary.

Please help me with the queries above. Thank you.

Regards
PG


Helpful links:
1: https://en.wikipedia.org/wiki/Broadcast_transmitter
2: https://en.wikipedia.org/wiki/Effective_radiated_power
3: https://en.wikipedia.org/wiki/Transmitter_power_output
 

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What a badly written piece of text.

"Overwhelms the contaminations" jeez! what a drama queen!

"Increasing power is costly and may damage equipment"
Of course it is costly, use more energy, burn more fuel, pay more money.
The equipment will only be damaged if it is not correctly designed for the required power level.

"High voltage rupture" Yes one of the early cables did fail due to too much voltage being used to try and overcome the losses.
The voltage used was too high for the dielectric (insulation) in the cable, and so the insulation broke down.
Why didn't the idiot who wrote that text just say that!

JimB
 
What a badly written piece of text.

"Overwhelms the contaminations" jeez! what a drama queen!

Agreed. The text was taken from this book.

"High voltage rupture" Yes one of the early cables did fail due to too much voltage being used to try and overcome the losses.
The voltage used was too high for the dielectric (insulation) in the cable, and so the insulation broke down.
Why didn't the idiot who wrote that text just say that!

Once again, agreed. Actually one of the main problems I'm facing in this course is that I couldn't find a good book and the book being used is not good at all. Now I'm taking help from almost five books. One of the books Data Communication and Networking by Behrouz is good at explaining some basic concepts.

By the way, is there some phenomenon called 'power leakage' which comes into effect if too much power is used for transmission? I heard it from someone but I doubt it. Kindly let me know. Thanks.

Regards
PG
 
is there some phenomenon called 'power leakage'
I have never heard that expression, can you put some context to it?

JimB
 
Thank you.

I have never heard that expression, can you put some context to it?

JimB

I just heard some guy using that expression and there is no further context. Let's forget it. Thanks, anyway.

Regards
PG
 
PG,

About "power leakage", why not just ask the person who made the comment to explain what he means? Sometimes terminology is used in smaller circles and it not universally understood.

Where is the power leaking to? Perhaps he means power leaking into other parts of the frequency spectrum, which is normally a very bad thing since it will interfere with other channels. For this to happen from too much transmission power, the medium would need to become nonlinear for high power. This can't happen in vacuum and is not likely to happen in free space air transmission, but it can happen with optical fiber, and possibly (although less likely) other types of waveguides with radio and microwaves. It's also possible that it's not the transmission power, but the modulation is over 100% which causes spurious frequencies (harmonics). This is not transmission power, but signal amplitude causing the issue. As far as transmission power, any device that handles the transmission signal (amplifiers, antennae, cables etc.) and becomes nonlinear could cause spectral power leakage of this type.

Optical fibers can actually utilize such nonlinear effects. Stimulated Raman Scattering is normally bad if it happens to the signal power being too large, but it is possible to amplify smaller signals using Raman gain which involves putting a high power "pump" laser in at another frequency. The pump power then is transferred (in other words power is leaked, so to speak) to the signal power and the signal is amplified. The pump laser frequency is out of the band of normal signals, so there is no issue with killing any channels.

So, to answer your question, there are phenomena that could be described as "power leakage", but we can't know what the person you talked to actually meant without clarification from him.
 
what if modulation isn't used

Thank you, Steve.

I will try to ask that guy. But I think he won't know because I have seen people using fancy expressions without really knowing what they are all about.

I will expand on that example of microphone from Q3 in this post which we were discussing yesterday. Please note that you can also ignore the mentioned microphone example from the other post altogether because it's not that much relevant here.

Re: What if we don't use carrier signal or in other words what if modulation isn't used.

By 'microphone' I'm specifically referring to carbon microphone. Assume that there are no other radio channels or broadcast present in the area. We intend to build a local radio station. As a steady direct current is passed between the plates of the microphone, the varying resistance results in a modulation of the current at the same frequency of the impinging sound waves. Here we can say that we have a carrier signal with frequency of 0 Hz. Then, this signal is amplified and then fed to transmitter. Here note one thing that audio signal has frequency range from 300-3300 Hz and relation for EM waves is v=fλ where 'v' can be taken to be 300000 km/s, and it means λ is going to be from 1000000 m to 90909 m. This wavelength range indicates first problem we can face because efficient and good antenna (or, optimum antenna size) should be 1/2 or 1/4 of a average wavelength. Q1: Do you think it's a serious issue?

Every household has an antenna which receives radiated radio waves from the transmitter and then received signal is amplified and fed to speaker system. Q2: Do you think such a radio station can work? Even if it works I do believe this won't work if another radio station is build the same way in the same area.

Q3: Are there any other issues we can face?

Please help me. Thank you.

Regards
PG
 
A baseband radio transmitter would be very impractical. You are talking about antennae the length of countries and small moons. It's not impossible in principle, but completely impractical. Another issue is the wavelength range changes by 1 order of magnitude. When you modulate, the wavelength is determined by the high frequency carrier and the signal content does not changes this appreciably.
 
Thank you, Steve.

Q1:
A baseband radio transmitter would be very impractical. You are talking about antennae the length of countries and small moons. It's not impossible in principle, but completely impractical.

Is this really completely impractical? Do you mean to say it won't work at all? In reply to Q4 here, Jim said,

JimB said:
Polarisation.
If the elements of the antenna are horizontal, it is said to be horizontally polarised.
Similarly, if the elements of the antenna are vertical, it is said to be vertically polarised.

The antennas at both ends of a link should be of the same polarisation, otherwise there will be a BIG loss of signal (in practice, about 20 or 30dB).

The same it true for whip antennas!
The whip antenna on a broadcast radio litening to a local station has so much signal that the loss due to incorrect polarisaion is not usually noticed.

Therefore, I conclude polarisation doesn't matter really matter if the signal is strong. This leads me to believe that antenna size won't matter either if the signal is not weak. But polarisation of antenna and antenna size would matter when the signal is weak and the receiver is situated at quite a distance from transmitter. I know from practical experience that a TV set can pick up local channels even when no antenna is attached to it. So, do you you really think antenna size would really matter when we are talking about coverage area of only , say, 3 km?

Q2:
Another issue is the wavelength range changes by 1 order of magnitude. When you modulate, the wavelength is determined by the high frequency carrier and the signal content does not changes this appreciably.

I'm sorry but I don't really get it. I understand what you mean by order of magnitude; e.g. if value changes from 10 to 100, we say that it changes by 1 order of magnitude. And if frequency division multiplexing is used, then, as you say, frequency of the carrier doesn't change that much by the signal.

Thanks a lot for the help.

Regards
PG
 
I say it's impractical because the transmitting antenna and receiving antenna both need to be large to have appreciable efficiency. When you say 3 km coverage area, this is even smaller than the antennae size we are talking about. So, the physics makes it impractical and the usage makes it impractical. Might it be possible to demonstrate a crudely working system? Maybe, ... I'm not sure, but nothing that results could be deemed practical.

Also, what I mean about the order of magnitude is that the frequency is changing from 300 Hz to 3000 Hz, which implies the optimum antenna size is changing. Hence, the antenna needs to be a broadband antenna (making it bigger and less practical) or the antenna will act like a filter and accept some frequencies better than others. The efficiency problem exists for both the transmitting and receiving antennas. This itself does not make the system impractical since intelligible speech could still be obtained, but it is a severe drawback to a system.

Note that frequency division multiplexing might require different antennas or a broadband antenna to get all of the channels. TV antennas have varying length dipoles on them to receive all stations. But, any one channel does not have the signal affecting the antenna efficiency. Whereas, your carrier-less concept has the transmission bandwidth covering 1 order of magnitude in frequency. That creates an unnecessary challenge to transmitting and receiving.

Bottom line is that modulation with a carrier to anything higher in frequency is only going to help you overcome all of these practicality issues. Even shortwave at 1 MHz is going to do so much better. At least there you can string an antenna that is large, but still fits on your property and get good reception. As you go down in frequency it gets harder and harder. Maybe 100 kHz could do something, but I doubt anything below this would be interesting.

More information about this low frequency band can be found here.

https://en.wikipedia.org/wiki/Extremely_low_frequency
 
Is this really completely impractical? Do you mean to say it won't work at all? In reply to Q4 here, Jim said,
Yes it is totally impractical.

Consider 3kHz, wavelength is 100km.
If we use an antenna which is 100m long to try and transmit our "local radio station", that antenna will be 0.001λ long.
Compare this with 100MHz, wavelength is 3m
At 100MHz a 0.001λ antenna would be 3mm long. This is not going to radiate much of a signal.

JimB
 
FM and AM radio

Hi

Why FM radio staion has less range than AM radio station? Is the answer below a good one? Please let me know. Thanks.

AM has a better range because they allow more power to be pumped out than FM. Why? Because we want them to be that way. If a station has a shorter range then you can cram more into a geographic region, so we limit the power on FM stations to get more licenses, more advertising etc. The market is not as big for AM radio so we allow them to cover a larger territory, but there is really nothing stopping us scientifically from making an FM transmitter super powerful and AM stations weak. - Yahoo Answers

This link is also very useful here.

Regards
PG


Helpful links:
1: http://stereos.about.com/od/stereoscience/a/AMFMRadio.htm
2: http://www.cybercollege.com/pix2/ionosph.gif
3: http://4.bp.blogspot.com/_ZJIVbYKv5mY/S7Vh_46FeUI/AAAAAAAAAAk/7f0ADNXoKfc/s1600/fmionos.gif
4: http://uascience09.blogspot.com/2010/04/radio-wave-characteristics-and-quality.html
5: **broken link removed**
6: http://ete.cet.edu/gcc/style/images/uploads/student pages/earth-atmosphere-layers.jpg
7: **broken link removed**

(The ionosphere is a region of the upper atmosphere, from about 85 km (53 mi) to 600 km (370 mi) altitude, and includes the thermosphere and parts of the mesosphere and exosphere.)
 
Last edited:
Is the answer below a good one?
No, it is a fairly lame brain moronic answer.

Look at answer number 2 in Yahoo answers, that is much better.

The information in the LINK is quite good, and your Helpful Links is also quite good.

What many people just plain FAIL TO UNDERSTAND is that the range is nothing whatsoever to do with it being AM or FM.

The RANGE is all about the FREQUENCY.

The Medium Wave Broadcast Band, note my words, Medium Wave Broadcast Band, is in the frequency range 520 to 1600kHz (or there abouts).
One of the characteristics of these frequencies is that they will reflect off the ionosphere giving increased range.
That Amplitude Modulation is used is incidental, and there because of historical reasons dating back to the 1920s.

The VHF Band 2 Broadcast Band is in the frequency range 88 to 108Mhz.
VHF range is limited to line of sight ranges and does not reflect from the ionosphere.
FM was used here because the bandwidth required for wide deviation FM is available.

JimB
 
Hi

All EM waves undergo three physical phenomenons which are reflection, refraction (bending due to change in transmission medium), and diffraction (spreading after encountering an obstacle). Suppose you point a powerful dot-thin red laser beam at moon, ignore all the air and water particles etc. That dot-thin beam will become quite a huge size red spot after reaching the surface of moon. Because when the beam exits the aperture, it sees it an obstacle and starts spreading. Another very important phenomena related to an EM wave is that of ability of penetrating solids such as concrete etc. (check first four links)

To most people line-of-sight communication means that two communicating devices should be able to establish a direct communication path between them without any obstacle therein. For example, before Bluetooth technology became prevalent, infrared communication between two cell phones required that the infrared sensors of both phones should be able to see each other. But such an understanding of line-of-sight communication is not all correct.

At this point also read through post #12 and #13 above, especially go through the links given in post #12. I believe both AM and FM are line-of-sight communications. AM signal can have global reach because of reflection from ionosphere. On the other hand, FM signal, which has higher frequency, doesn't reflect well from ionosphere and therefore has small range. If the earth were a plain surface which is to say no trees, building, mountains, air molecules, water particles, atmospheric layers etc. then you won't be able hear anything on your radio unless your radio and transmitting antenna can see each other. Because it would mean no reflection which play a dominant role if spreading of a signal. Q1: Do I have my understanding correct up to this point?

Infrared radiation has higher frequency range than that of AM and FM but it is comparatively bad at reflection etc. I'm saying this from my practical experience. Likewise, FM covers higher frequency range than AM and it is not as good at reflection as AM is. Q2: Is there some relation between frequency and reflection?

Please help me with the queries. Thank you.

Regards
PG


Helpful links:
1: http://www.fnal.gov/pub/inquiring/questions/mikep.html
2: http://van.physics.illinois.edu/qa/listing.php?id=1867
3: http://answers.yahoo.com/question/index?qid=20090213044924AAFkR8Z
4: http://answers.yahoo.com/question/index?qid=20100131124554AAY7jkP
5: http://en.wikipedia.org/wiki/Line-of-sight_propagation
6: http://en.wikipedia.org/wiki/Non-line-of-sight_propagation
7: http://www.cybercollege.com/frtv/frtv017.htm
8: http://www.techopedia.com/definition/5069/line-of-sight-los
9: http://forums.qrz.com/showthread.php?36714-FM-line-of-sight
10: http://www.zonalatina.com/Zldata126.htm
 
All EM waves undergo three physical phenomenons which are reflection, refraction (bending due to change in transmission medium), and diffraction (spreading after encountering an obstacle). Suppose you point a powerful dot-thin red laser beam at moon, ignore all the air and water particles etc. That dot-thin beam will become quite a huge size red spot after reaching the surface of moon. Because when the beam exits the aperture, it sees it an obstacle and starts spreading. Another very important phenomena related to an EM wave is that of ability of penetrating solids such as concrete etc. (check first four links)

This part seems spot on and accurate. Of course, penetrating simply means transparency. RF can go through concrete and light waves can't. This is independent of the line of sight issue, as you seem to understand.

To most people line-of-sight communication means that two communicating devices should be able to establish a direct communication path between them without any obstacle therein. For example, before Bluetooth technology became prevalent, infrared communication between two cell phones required that the infrared sensors of both phones should be able to see each other. But such an understanding of line-of-sight communication is not all correct.
The first part is my understanding of line-of-sight too, but you are correct to point out that terminology is rarely precise, and other meanings can come into play.

At this point also read through post #12 and #13 above, especially go through the links given in post #12. I believe both AM and FM are line-of-sight communications. AM signal can have global reach because of reflection from ionosphere. On the other hand, FM signal, which has higher frequency, doesn't reflect well from ionosphere and therefore has small range. If the earth were a plain surface which is to say no trees, building, mountains, air molecules, water particles, atmospheric layers etc. then you won't be able hear anything on your radio unless your radio and transmitting antenna can see each other. Because it would mean no reflection which play a dominant role if spreading of a signal. Q1: Do I have my understanding correct up to this point?

Here I would point out that the concept of line-of-sight with waves is a grey-scale not a black and white classification. You basically want to compare the wavelength with the dimensions of the obstacles. I think you will find that AM/FM is in the range where it is a mix of both line-of-sight and not line of sight, depending on the size of what's in the way. Obviously, AM would be less of a line-of-sight, than FM since FM has the higher frequency.

Infrared radiation has higher frequency range than that of AM and FM but it is comparatively bad at reflection etc. I'm saying this from my practical experience. Likewise, FM covers higher frequency range than AM and it is not as good at reflection as AM is.
I'm not sure why you mention reflection alone. Reflection and transmission go hand-in-hand and there are absorption/scattering effects and diffraction/refraction effects as you mentioned.

Infrared radiation covers quite a large range of wavelengths from 1 μm to 1 mm. That is similar to the RF range of 1 MHz to 1 GHz (I know the range is lower frequency too, but typically). Compare that with visible light which is 0.4 to 0.7 μm. Look at how the narrow visible range can display so many effects with color, reflection, refraction etc. So, IR with 3000 times more wavelength range will be hard to describe in general terms as far as comparing to RF with a similar >3000 times wavelength range. It would take a lot of research to really understand the comparisons, and I can't comment too much on this, since I haven't done the research.

Q2: Is there some relation between frequency and reflection?
Yes or course, but it is not simple. Various materials (conductors, dielectrics, and materials with complex conductivity/permittivity) would have very different characteristics. There is also strong dependence on incident angle. There are also absorption, scattering and other effects. Again I would say, think about what you see with visible light and all the variety with different materials.
 
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