prateeksikka Posted February 19, 2005 Author Report Share Posted February 19, 2005 hi audioguru! i exactly meant the way you thought..Did u have to purchase the frequency used by you from the authority or one is free to chose any frequency at which transmission is done.IN short can i make a transmitter that works at 115 Mhz. well beyond f.m range and that too without permission!!!!!!!????????prateek Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 20, 2005 Report Share Posted February 20, 2005 Hi Prateek,You should find out the rules and regulations of transmitters in your country.In Canada, anyone can transmit on the FM band with a power up to 100mW as long as they don't cause complaints about interference, profanity and stuff like that.You will be in big trouble if you transmit on RF frequencies reserved for aircraft communication, a little higher than 108MHz. Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 20, 2005 Author Report Share Posted February 20, 2005 audioguru!as far as i know we in india can transmit upto 100 mW in F.M range(88-108)Mhz. how can i ensure that my transmitted power does not exceed 100mW? for frequencies i think that we have to purchase the bandwidth from government.prateek Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 20, 2005 Report Share Posted February 20, 2005 Hi Prateek,You can assume that the transmitter is 50% efficient, then measure its operating current and voltage, multiply them to calculate total power used, and divide the total power by 2. If your transmitter doesn't have an output tuned circuit tuned to its operating RF frequency, then it will be transmitting many harmonics, each using some power, reducing the power for the main fundamental RF frequency.Higher power transmitters operate the final RF transistor in class-C (not biased) which is more efficient. I will try it with mine and measure the difference in transmitted strength with a simple RF meter I'll make. Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 20, 2005 Author Report Share Posted February 20, 2005 audioguru!how do you rate the idea of using low level modulation in this circuit?in that case we can almost blindly chose the amplifierprateek Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 20, 2005 Report Share Posted February 20, 2005 Hi Prateek,You shouldn't blindly choose a preamp for the FM transmitter. It should operate properly over the circuit's power supply voltage range. It should have the required amount of gain and have pre-emphasis, low distortion and a wide frequency response to sound right. Look at the preamp in the original circuit, it had everything wrong.An opamp would work better than a transistor, I'll try it next. Quote Link to comment Share on other sites More sharing options...
MP Posted February 20, 2005 Report Share Posted February 20, 2005 Audioguru,When posting a modification of someone else's circuit, we should mention where the original came from and give the original author credit for his work, no matter how you feel about it. Would you post the original for all to see? Or at least give us a link?MP Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 20, 2005 Report Share Posted February 20, 2005 Audioguru,When posting a modification of someone else's circuit, we should mention where the original came from and give the original author credit for his work, no matter how you feel about it. Would you post the original for all to see? Or at least give us a link?MPHi MP,Sorry, I don't know where the circuit came from. It might be very old and its author might not even still be alive. After all, I built the same kind of circuit 42 years ago.I was just helping someone who found the circuit and built this monster: Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 21, 2005 Author Report Share Posted February 21, 2005 hi audioguru!i have read that the world today is craving for bandwidth. thats why we are constantly moving towards higher end of spectrum just like GHz range in satellite communication. But it comes with a disadvantage that higher frequencaties are more prone to noise.is it true that high frequency means high distortion? if yes then why is it not applicable to high frequency F.M over low frequency A.M?(ANYBODY MAY HELP ME!!!!)PRATEEK Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 21, 2005 Report Share Posted February 21, 2005 Hi Prateek,I don't think microwave and UHF satellite TV and cell phones are noisy. My 900MHz wireless phone isn't noisy. Even the 100MHz VHF FM band isn't noisy. They all work perfectly. My cable TV company sends signals 6000km using light frequencies (fiber-optics) and my reception is perfect.Also, the frequency of the carrier has nothing to do with distortion. Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 21, 2005 Author Report Share Posted February 21, 2005 AUDIOGURU!IF I HAVE 5mV SIGNAL (AMPLITUDE) AND I TRANSMIT IT AT 2 FREQUENCIES SAY 100Hz and 2Ghz .do u think that the two will be equally affected by noise?if not,which one is affected more?if noise effect is independent of frequency we could not be fighting for and paying huge bucks for purchasing bandwdth. prateek sikka Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 21, 2005 Report Share Posted February 21, 2005 Hi Prateek,I don't know about RF noise. I just know that noise doesn't affect the VHF, UHF, microwave and visible-light frequencies that I use.I have never purchased "bandwidth"except for the high-speed-cable that connects me to the internet. Its bandwidth is about 50 to 100 times as much as dial-up, but costs only twice as much. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted February 22, 2005 Report Share Posted February 22, 2005 Well a 100Hz signal would need a very large antenna 747.5km would do the job.Low RF frequencies are noisy as they are effected by noise from thunders storms and ignition systems as these noise together with the signal are reflected back to earth by the ionosphere.100Hz would be horrible the bandwidth is very low and with power companies transmitting power at 50Hz, and 100Hz is the 2nd harmonic that emitted by rectifiers and other AC power systems would cause lots of interference.2GHz would be a lot better, the bandwidth is bigger and it's i the low noise region where there's very little sky noise. The only disadvantage is it won't travel beyond the horizen and you're limited to only 100km or so even if you have the transmitter on a tall mast on the top of a mountain. For long distance transmition I would recommend 22MHz a happy medium between distance and bandwidth. Or you could use 2GHz with a satalite link. Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 22, 2005 Author Report Share Posted February 22, 2005 hi alun and audioguru!can i conclude that high frequency waves dont travel far because they mostly travel line of sight but have the advantage of low noise over loe frequency signal??????????plz reply prateek Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 22, 2005 Report Share Posted February 22, 2005 Hi Prateek,I wouldn't say that higher frequencies have lower noise, just that they have less interference. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted February 22, 2005 Report Share Posted February 22, 2005 The interference gets higher at even higher frequencies.At 22GHz resonance of water occures an 66GHz Oxygen resonates.As we go up in frequency rain and eventually atmospheric moisture becomes a problem. Transmitters become increasingly difficult to build at any decent power level and above radiation above 300GHz the atmosphere is opaque to radaiton only to become transparent again in the mid-infrared region.Having said that 100GHz is used in very high resolution radar and high speed data comunications.There is a gap in the electormagnetic spectrum called far-infrared/submilimeter RF, between 300GHz and 30THz that's hard to study because lasers are hard to make wavelenghs longer than 10 Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 22, 2005 Author Report Share Posted February 22, 2005 hi audioguru!very less interference at very high frequencies.microscopic pocket antenna to transmit,what else do we desire?wat is the problem at such high frequencies?can we expect our radio services to run at few Ghz in near future?prateek Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 22, 2005 Report Share Posted February 22, 2005 Hi Prateek,GM already has OnStar satellite help for their cars and next year (in a few months for cars) they will have your "satellite radio services running at a few GHz". Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted February 22, 2005 Report Share Posted February 22, 2005 hi audioguru!very less interference at very high frequenciesNo as I've already said the interferance gets worse beyond a certain point in the RF spectrum because the molacules in the air resonate and noise from stars gets worse too.If you want low noise transmision use the low noise window between 2 and 8GHz, but it gets a lot more noisy above 10GHz..microscopic pocket antenna to transmit,what else do we desire?wat is the problem at such high frequencies?Transistors don't work at reasonable power levels at these frequencies so magnetrons and klystrons are used these are often very big and bulky.can we expect our radio services to run at few Ghz in near future?Many already do satalite TV works at around 5GHz. Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 23, 2005 Author Report Share Posted February 23, 2005 hi guys! i have heard that bandwidth is precious ! save it!why is it the case when we are safely moving towards higher end ofspectrum(upto tera hz)?????IS BANDWIDTH REALLY A THING TO PRESERVE????PRATEEK Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted February 23, 2005 Report Share Posted February 23, 2005 More bandwidth means more data per second.Low THz frequencies aren't used but the higher 300THz near infrared is used in fibre optical comunications. This is way above the frequency that normal transistors work at so LEDs, lasers and photo diodes are used instead. Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 24, 2005 Author Report Share Posted February 24, 2005 hi all!hi bandwidth and high frequency differ.does working at high frequency ensure high bandwidth for the device?what do we desire,high bandwidth or frequency?prateek Quote Link to comment Share on other sites More sharing options...
trigger Posted February 25, 2005 Report Share Posted February 25, 2005 no, high frequency do not mean high bandwidth.It depends on the modulation, the coding , the filtering and the processing power on both transmitter and receiver (in case of digital communication).I prefer high bandwidth more than high frequency. Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 25, 2005 Author Report Share Posted February 25, 2005 hi alun!do you have any idea of chosing the 88-108 MHz as band width of FM and not say 100-104Ghz?dont you think that it will ensure much smaller height of antenna?why dont we use that high frequencies? Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 26, 2005 Author Report Share Posted February 26, 2005 hi allcan anyone of you tell me why no TV has a grounding third pin,it always has a 2 pin shoe connecting it to supplyprateek Quote Link to comment Share on other sites More sharing options...
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