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#1
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Michael A. Terrell wrote:
duckman wrote: Is there available, can it be done to have an AM and/ and or FM transmitter that will broadcast over the entire AM and FM broadcast band at the same time. Or at least multiple stations. E.G. Not with a single transmitter. You could build a comb generator and modulate it for AM, but the quality would be poor For FM you either need separate transmitters, or modulate the signal and mix it with a separate oscillator for each channel Nah, given a wideband signal source and amplifier, there's conceptually no reason he couldn't broadcast on all stations simultaneously! I find it a novel idea, actually. The big question is why you would want to do it. I suspect he's thinking of something like those 'talking houses' where you're supposed to tune your radio to a given station and get information on why you want to drop a quarter million bucks on a thousand square feet of your very own sometime in the next 20 minutes... except he doesn't want people to have to tune at all! Slightly less evil would be emergency broadcasting type uses... ---Joel Kolstad |
#2
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Joel Kolstad wrote:
Michael A. Terrell wrote: duckman wrote: Is there available, can it be done to have an AM and/ and or FM transmitter that will broadcast over the entire AM and FM broadcast band at the same time. Or at least multiple stations. E.G. Slightly less evil would be emergency broadcasting type uses... Apparently someone believes it's possible as an application was recently filed with the FCC for an experimental license to operate just such a system across the FM band. (the Commission denied the application) Their intent was to install transmitters on emergency vehicles, so they could warn other motorists to get out of the way. My guess is the FCC feared these devices would "get out into the wild" - can you imagine what an unscrupulous nightclub owner (or someone with a political bone to pick) could do with a few of these? -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
#3
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If you want to put up a signal that covers a wide band, you will
essentially need a spreading function. In your case, there is no corelation that will de-spread the signal at the receiving end, now, regardless of the technique you employ to achieve this transmission, one thing is sure, you will need some really heavy power. imagine that you can cover 300 meters using a 10mW transmitter. Now, this transmission is received by a receiver with a selectivity of about 50KHz. If you were to cover such a signal every 50KHz for 1MHz, you will require 1000/50 = 20 times as much power, that is, about 500mW. Correspondingly, if you wanted to transmit over a 10MHz bandwidth, you will require 5Watts output to achieve the same result. Now, lets move onto the next part: what kind of modulation? Frequency modulation requires that the carrier should shift. Therefore, if you modulated broadband noise, it wouldn't do. You will have to put out carriers every 50KHz. This will require a comb generator. Hers is how, pass the carrier through an XOR gate and feed the other input of the XOR gate with a 50KHz carrier. This will keep flipping the phase by 180% and generate sidebands. The strength of the side bands will depend upon how square your 50KHz carrier is. The carrier can be frequency modulated as normally done. This is a quick and dirty method. there are a number of problems with this approach, first, there is really no way of limiting the signals to a particular band unless you do extensive amount of filtering at the output. second, the signals will be the strongest in the center and taper off exponentially (not really, but actually) towards the edges of the band. |
#4
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Joel Kolstad wrote:
Michael A. Terrell wrote: duckman wrote: Is there available, can it be done to have an AM and/ and or FM transmitter that will broadcast over the entire AM and FM broadcast band at the same time. Or at least multiple stations. E.G. Slightly less evil would be emergency broadcasting type uses... Apparently someone believes it's possible as an application was recently filed with the FCC for an experimental license to operate just such a system across the FM band. (the Commission denied the application) Their intent was to install transmitters on emergency vehicles, so they could warn other motorists to get out of the way. My guess is the FCC feared these devices would "get out into the wild" - can you imagine what an unscrupulous nightclub owner (or someone with a political bone to pick) could do with a few of these? -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
#5
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If you want to put up a signal that covers a wide band, you will
essentially need a spreading function. In your case, there is no corelation that will de-spread the signal at the receiving end, now, regardless of the technique you employ to achieve this transmission, one thing is sure, you will need some really heavy power. imagine that you can cover 300 meters using a 10mW transmitter. Now, this transmission is received by a receiver with a selectivity of about 50KHz. If you were to cover such a signal every 50KHz for 1MHz, you will require 1000/50 = 20 times as much power, that is, about 500mW. Correspondingly, if you wanted to transmit over a 10MHz bandwidth, you will require 5Watts output to achieve the same result. Now, lets move onto the next part: what kind of modulation? Frequency modulation requires that the carrier should shift. Therefore, if you modulated broadband noise, it wouldn't do. You will have to put out carriers every 50KHz. This will require a comb generator. Hers is how, pass the carrier through an XOR gate and feed the other input of the XOR gate with a 50KHz carrier. This will keep flipping the phase by 180% and generate sidebands. The strength of the side bands will depend upon how square your 50KHz carrier is. The carrier can be frequency modulated as normally done. This is a quick and dirty method. there are a number of problems with this approach, first, there is really no way of limiting the signals to a particular band unless you do extensive amount of filtering at the output. second, the signals will be the strongest in the center and taper off exponentially (not really, but actually) towards the edges of the band. |
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