helloo all ,
long time ago i did a research about radio and how does it work.


i have an idea that pop to my mind,

connect to the parrelal port\microphone input an anttena , and then receiving all data to a computer program and let the software do all the moduling with FM\AM and etc.....

my question: does it make sense? maybe i need to build something between the antenna and the computer?

thanks

eko
Posted on 2007-12-01 09:12:28 by eko
Well, first of all you would have to amplify the signal from an antenna quite a bit before the port can see it, also the parallel port would be useless as it is a digital port and (standard) radio is an analog signal. Moreover the analog input ports on the outside of your PC are far too slow to process the carrier wave frequency. What you would need is a high speed amplifier, ADC and an appropriate port chipset for communication and handshaking etc... and you would still have huge design issues to overcome, best to build a digital radio and plug it directly into a slot on your PC. This is not a simple task or design issue, it might be an interesting project if you have the time and skills but if it is to build a cheap PC radio well they are only a few dollars anyway, much cheaper than you can build it for.
Posted on 2007-12-01 09:29:01 by donkey
i have great intresting in radio , and i'm tring to find a project which involves many of old items i have that dont have any more use .

when you say adc , i think about an old modem i have here.
does a modem fast enough to do the trick?

anntena -> modem -> computer - > software
analog data - > digital data - > software that will understand the frequency of carreir
wave , the modulation and play it

tell me what you think

bye

eko



Posted on 2007-12-01 17:10:42 by eko

i have great intresting in radio , and i'm tring to find a project which involves many of old items i have that dont have any more use .

when you say adc , i think about an old modem i have here.
does a modem fast enough to do the trick?

anntena -> modem -> computer - > software
analog data - > digital data - > software that will understand the frequency of carreir
wave , the modulation and play it

tell me what you think

bye

eko


Without physical modification of the supporting circuitry, the ADC/DAC of the modem will be of no use.
Posted on 2007-12-01 19:42:12 by SpooK
Hi eko,

I think just by the nature of the questions you are asking that you have some misunderstanding of how radio signals are transmitted and how interfaces to a PC work. You should do a bit of research into radio and perhaps try to build a stand alone one first, it will help you to grasp the complexity of what you are trying to do. Once you have built a 'normal' radio you can look at interfacing it to your PC.

Donkey
Posted on 2007-12-02 00:21:21 by donkey
I agree with donkey. Take any excuse you can to play with transistors!!!

In general, it sounds like you've contemplated two incompatible ways of detecting and receiving radio signals.

Microphones work off audio waves, i.e. molecules of air bumping into each other as the transmission medium, and converts them to fairly weak electrical signals.

Modems work off of analog electrical signals, i.e. electrons bumping into each other as the transmission medium, with light waves/fiber optics as a potential intermediate medium these days, and converts them into extremely weak DC voltage (digitally efficient) for the computer to process. This, of course, is done in reverse for sending... hence "modem" (moulator/demodulator).

Radio waves are a form of radiation that falls within the electromagnetic spectrum, with fairly long and low frequency waves. Those goofy looking antennas respond to this physical radiation and that energy is converted into not-so-weak electrical signals that are processed.

Basically, unless you provide some circuitry that will directly process modulation/frequency/etc... information, you will find it hard to accomplish your goal and attempting to interface using these other methods is rather useless since you will lose signal fidelity along the way.
Posted on 2007-12-02 03:40:28 by SpooK
Yes, and don't forget that the tuning will probably have to be done outside the PC, this is simply because it requires a band pass filter (usually an RC or PLL) in order to pass only one radio frequency at the exclusion of others. I can't think of any way to mimic this behavior using a PC without extra circuitry.

Anyway you might start here...

http://www.howstuffworks.com/radio-spectrum.htm
http://www.dxing.com/index.html
Posted on 2007-12-02 09:50:25 by donkey

Yes, and don't forget that the tuning will probably have to be done outside the PC, this is simply because it requires a band pass filter (usually an RC or PLL) in order to pass only one radio frequency at the exclusion of others. I can't think of any way to mimic this behavior using a PC without extra circuitry.


If you could manage to convert those electrical signals into some digital equivalent, perhaps. However, I don't think your computer's data bus would be able to handle all that information in real time... something would have to go.

This is mainly why you find TV/Radio input cards that have circuitry that performs the required frequency isolation and whatnot then passing it to some sort of acceptable converter that outputs a format that your computer can easily handle, e.g. streaming MPEG.

Basically, imagine having millions of people talking to you at once in all different languages... this is still too much data for your computer to physically/electrically process all in real time.
Posted on 2007-12-02 12:34:55 by SpooK
No, the data bus could not handle the carrier frequency, if you take a common station like 107.1 then you are looking at 107 Mhz, if you sample a wave 50 times (which is not fast enough to retain any usable information from the modulated portion), you are still looking at a minimum bus freq. of 5 Ghz, that is real time and it must have exclusive use of the bus, not something that is possible in a Windows environment. Even at that it would have to be a tuned channel. The tuning must be done externally and the carrier stripped leaving a modulated audio signal, at that point it can easily be sent through the LINE IN of your PC. Channel selection could be done using a digital PLL and the parallel port so it might be better to just use the parallel port to receive the audio signal, it's more than fast enough for the 20Khz necessary.
Posted on 2007-12-02 17:50:03 by donkey
hey all , thanks for replys .

about radio in software http://en.wikipedia.org/wiki/Software-defined_radio
they try to get minimum hardware as they can to get radio, i now understand that for computer it will hard to handle too much FPU funtions on lots of data. but there is lots of information about "software defined radio" over the net

my goal was to do the tuning in sofware and not control an outside radio via computer.

i read alot about radio , and now how it works - understand the theory behind ,  but  i dont know how actully do the calculation and logical gates with electronics(transistors)

Posted on 2007-12-03 11:24:00 by eko
Well,

As I understand it, a "Software Defined Radio" has little to do with interfacing a radio to a normal PC, actually most work in that direction involves highly targeted specific PCs which are designed with the radio in mind. SDR is a project that will allow computer control over signal processing of radio waves and give a wider range of options to manufacturers of radio frequency equipment such as GPS, wireless services, cellular etc... that would be reconfigurable within software to meet the needs of the user and standards anywhere in the world. Quite a complex project which many companies are working on with mixed results. However, the wiki article you linked does mention that a superheterodyne system would solve many of the tuning related problems since it will convert any band to a single predetermined frequency that can then be handled using fixed hardware.
Posted on 2007-12-03 17:43:31 by donkey