supper simple transmitter question

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LucidGuppy
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supper simple transmitter question

Post by LucidGuppy » Mon Jan 24, 2005 5:36 pm

http://www.scitoys.com/scitoys/scitoys/ ... itter.html<p>Has a super simple computer controlled transmitter. Would this be a practical circuit for hobbyists? Is it low power enough to be fcc compliant? The site uses an am radio for demodulation and only transmits morse code. Could this be changed into a really slow baud serial wireless link? Any ideas?<p>Thanks
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Re: supper simple transmitter question

Post by jimandy » Mon Jan 24, 2005 5:50 pm

Is that 1 Mghz oscillator actually a TTL clock chip? If so I would think the square wave it generates is full of rich harmonics that otherwise would be called "interference" to those unlucky enough to receive them.
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Re: supper simple transmitter question

Post by philba » Mon Jan 24, 2005 6:40 pm

That's pretty cute. It probably flies under the FFC power requirements. I'd guess the circuit consumes no more than 20 or 30 milliwats (10V * 2 mA or so) - you dont get a lot of current out of DTR. I'd bet radiated power is quite a bit less than that. Yeah, you could probably make it transmit serial data but you'd have to build a receiver - you'll need to do some filtering to make the received data compatible with the serial I/O input. I don't know enough rf engineering to be of help there. I do know that your max baud rate will depend on how quickly the crystal goes into oscillation. <p>Were you aware that you can buy transmitter/receiver pairs for pretty cheap? Lots of places sell them. For example, http://www.sparkfun.com/shop/index.php? ... 089&cat=62&
scroll down to "Simple RF Link - Transmitter - Receiver". $11 for a tx and RX pair.

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Re: supper simple transmitter question

Post by terri » Tue Jan 25, 2005 11:56 am

That is pretty slick. <p>I believe all of those oscillators run on 5V, by the way --although that's fairly nominal.<p>[ January 25, 2005: Message edited by: terri ]</p>
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Re: supper simple transmitter question

Post by jollyrgr » Tue Jan 25, 2005 3:12 pm

This actually does work. I have a bunch of these TTL trans.. er um oscillators and they are super simple and work fairly nice. I bought a grab bag full of them and have some in the middle of the FM band. I connected a short piece of wire to the output (about three feet) and connected a 4.5 volt (3 AA cell) battery pack to one set at 99.54xxxMHz. I don't know why they got it so precise but the marking goes out to five decimal places; ####7 for the part I cannot recall. Especially since it wound up in a "junk box grab bag". Anyhow I can tune an FM radio to this frequency, more or less, and power up the thing. Full quieting at that frequency but not too much else noticable on the FM band. (I did'n try the second and third harmonics though.) I can take this out to the front of my house and still hear it on my home stereo. Leaving it on in the house and going out to the car stereo still has it showing up.<p>As far as the circuit shown, they DO mean a LONG wire. You can put a super long wire on this one and get a nice signal.<p>As far as hobbyist using this, this is being done by amateur radio operators. They get one with a in the HF ham bands and then add a "shaping" or tuned circuit to the output to get rid of some of the squarness of the signal. Then using a Morse code key try and make contact. This is called QRP or "extremely low power" communications. Experimenters use watch batteries for flea power communications. The goal is to see how many thousands of miles per watt you can go with this lower power. My description of the circuit is overly simplistic but gives you the idea.<p>A very neat idea to use the serial port of a computer to provide power AND an easy way of sending Morse code. I personally do not care for Morse code and have not used it on the bands. <p>In the example shown you would get a nice solid carrier right in the AM radio band. (Do realize that 1.000MHz is 1,000kHz on the AM dial.) It should be possible to build a simple AM VOICE radio transmitter using this TTL oscillator. My guess would be that connecting a carbon microphone (like those found in the "old style" telephones mouth piece) in series with the DC supply could make the amplitute vary enough to be heard on an AM radio but this is just a guess.<p>[ January 25, 2005: Message edited by: Jolly Roger ]</p>
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Re: supper simple transmitter question

Post by Chris Smith » Tue Jan 25, 2005 3:50 pm

I took a quad square wave chip [?LS123?] back in the 80s and drove it with 9 volts intended to drive a laser diode, and placed a UHF loop antenna on its out put instead of driving the laser diode. <p>For the little power it would draw, the FCC was on my door step within hours even though they never found out where it was coming from other than a good guess, while the neighborhood couldnt receive much of anything in the form of radio waves, including cable TV. <p>My Tek Oscilloscope couldnt even shield the noise this thing created, nor could the closed circuit TV. <p>Be carful if you add a efficient antenna, it may do a lot more than you bargain for. Mind you my system was set in the nanosecond range.

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Re: supper simple transmitter question

Post by terri » Tue Jan 25, 2005 8:14 pm

Chris, I wonder if the four-terminal oscillator to which you hooked the loop antenna might have happened to be a color burst oscillator --or near the color burst frequency (or its harmonics). <p>Nothing will incense the public more than if you trash up their TV sets --and the color burst frequency interference problem will pertain even if the TV viewer is on cable.<p>This might be the reason Riley was on your case so fast. The cable viewers probably complained to the cable provider, and they came out with their sniffers and pinpointed the problem to your area. They were probably the ones who called Riley.<p>Either that or you were trashing up some seekrit government frequency or something like that.<p>I too have a grab bag full of these four-pin oscillators and I used them to align and calibrate an old QRP rig, sometimes using the very rich harmonics on them to obtain a frequency in the ham bands.<p>The carbon mike is a neat idea. While I was playing with them, I wondered what would happen if one stuck a condensor mike across the power terminals... would it generate an FM signal by "rubbering" the internal crystal? Or would the condensor mike vary the input power as it changed capacitance and therefore generate an AM signal? Or both? Or nothing? But, being the diligent Ham that I am, I was slightly discouraged because of spectral purity concerns... despite the low power involved.<p>I never got around to picking up one of those condensor mike cartridges until recently and discovered that, at least according to the diagram on the back of the package, there was apparently an amplifier inside them... what would the effect be? I wondered.<p>I also wondered what would happen if I hooked a varactor diode across it, and drove that, or just modulated the power terminal directly, as with a modulation transformer.<p>But that was going too far from my original spark of curiousity. After all, hang enough stuff on the little four-terminal oscillator, and you might as well build a little FM xmtr in the first place, using more suitable components. And that's not what I wanted to do. I just wanted to try a simple add-on to the oscillator.<p>So, since this wasn't even a "back burner" project, and had a very low, low priority, I never got around to actually even trying the condensor mike, even though it's been sort of in the back of my mind for years and is so simple to implement.<p>So now, motivation heightened because of this thread, I might actually get around to trying it. Maybe next week. Maybe. Where are my Bravado Pills?<p>Man, I love this board. But I gotta watch my time budget on it --it's too, too seductive!<p>[ January 25, 2005: Message edited by: terri ]</p>
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Chris Smith
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Re: supper simple transmitter question

Post by Chris Smith » Wed Jan 26, 2005 9:13 am

I tested it the next day for all the band widths I could find.<p> From low AM through high FM radio, TV on all channels including Cable, CCTV [6mhz] and every other device I could test. It was extensive at what it wiped out.<p> Actually there was an article in NV back a few months ago about this method being “magnetic waves” VS Radio or EM waves? Ill have to dig it out and Re-read the article. The former being far stronger than EM, but with less distance over all.<p>The chip was a Quad Flip flop picked for its speed.

The only numbers I remember was the 123+ LS?<p>From memory it was set for minimum time on, followed by long delays between the flip/flop [980,000 ns off /200ns on at 1kz] and was originally intended to drive a current switch carrying 50 to 100 amp pulses at this speed . The latter was not connected to the loop antenna as it would have probably cooked any one near it.<p>[ January 27, 2005: Message edited by: Chris Smith ]</p>

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Re: supper simple transmitter question

Post by terri » Sat Jan 29, 2005 3:04 pm

My coffee-table computer is 133 MHz and when I turn it on it will break the squelch on my 2M rig sitting on the end-table next to me. So I've either got a lousy front end on my 2M rig or the harmonics generated by this computer must be odd, even, fractional, divided and multiplied by pi, e, Planck's constant, phi, Avogadro's number, and the square root of 2.<p>I suspect the latter, like your four-terminal oscillator.<p>'Course, it would probably help if I put the screws back in the computer's case, no? I'm into that computer so much I know I'm going to have to marry it soon.<p>Sorry. Just feeling whimsicalish tonight.<p>[ January 30, 2005: Message edited by: terri ]</p>
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Chris Smith
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Re: supper simple transmitter question

Post by Chris Smith » Sun Jan 30, 2005 11:11 am

Square wave osc are stronger than the others for noise value.

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Re: supper simple transmitter question

Post by terri » Wed Feb 02, 2005 5:30 pm

Just from memory, aren't true sawtooth waves the worst? I seem to recall that they contained all the even harmonics on the leading edge, and all the odd harmonics on the trailing edge. Or something like that. But I'll tell you what. This was such a long time ago that I wouldn't bet a nickel on my recollection.<p>Oh, wait a minute. I guess white noise is the worst, but that's not a "frequency" as such. I'm confused. I remember building a diode noise generator to check S/N in receivers. It could be picked up anywhere on the band. Maybe somehow that was what was happening with your four-terminal oscillator that was trashing up all those frequencies. ( ? )<p>Somebody please hit my "refresh" button.<p>[ February 02, 2005: Message edited by: terri ]</p>
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Chris Smith
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Re: supper simple transmitter question

Post by Chris Smith » Thu Feb 03, 2005 8:39 am

Square wave has the strongest signal, because there is more “on” value than sine or triangle.
Once attached to other devices, hash or noise can be created exponentially.

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Re: supper simple transmitter question

Post by jimandy » Thu Feb 03, 2005 9:41 am

terri said <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr> I remember building a diode noise generator to check S/N in receivers. It could be picked up anywhere on the band. <hr></blockquote><p>With all the buzz about the miracles of UWB (Ultra Wide Band) you guys may need to take credit for some of it's early development. :p
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Chris Smith
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Re: supper simple transmitter question

Post by Chris Smith » Thu Feb 03, 2005 1:07 pm

Most of the noise that you speak of came not from the wave type, but from the method of producing the type of wave from. <p>A true and clean square wave is the most powerful, but if its clean it needs something to dirty it up if you want to block other signals.<p> ELF is a wave form that is a very clean sine wave, up to ten miles between a single wave form, front, or edge, and even the earth and oceans wont stops it travels. However, it dosent bother other transmissions. <p>There is strong, clean, dirty, and efficient. All of these factors are different.<p> If you take a small square wave and dirty it up like many of the oscillators produce while making a triangle wave, you will have a more powerful hash or dirty signal. <p>The reason a diode can be real dirty is that internally as it passes current, it operates much like a pop off valve in a pressure cooker, but the speed at which the tiny bursts happen can be in the mega, giga, or even Tera hertz range, thus lots of noise is generated. And the diode it self because of its design, makes a perfect emitter and Antenna. Often diodes are placed against a parabolic antenna as a emitter in a feed horn and used to produce a microwave signal.

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Re: supper simple transmitter question

Post by terri » Thu Feb 03, 2005 8:51 pm

Well, I was really thinking of periodic waves, and white noise can't be considered "periodic," even though periodic components can be selected (bandpass filtered) out of white noise. (As with diodes in u-wave generation.)<p>Maybe there's more "transmission power" in a square wave, but I was only wondering what waveform had the most capability for trashing up communications because of its harmonic content.<p>I also wanted to differentiate between a triangle wave and a true* sawtooth wave. Triangle waves contain all the even harmonics and square waves contain all the odd harmonics, and I thought I remembered that sawtooth waves somehow contained all or almost all of both. Again, this would be because of the "triangle-like" leading edge and the sudden "square-wave-like" trailing edge. But I could be misremembering.<p>So that's why I wanted my refresh button hit. No big deal. Just wondered how come one of those four-pin oscillators could be as "trashy" as it was as to wipe out so much spectrum.<p>----------
*As opposed to a sawtooth wave which is only approximated by chopping a sine wave --which doesn't give a genuinely linear ramp-up to the peak.<p>[ February 03, 2005: Message edited by: terri ]</p>
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