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tackyattack
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I am building a HAM radio transmitter. I have noticed most crystal oscillators above 100mhz are very hard to find. Is there any way to multiply an oscillator's output, say, four times?
tackyattack said:I am building a HAM radio transmitter. I have noticed most crystal oscillators above 100mhz are very hard to find. Is there any way to multiply an oscillator's output, say, four times?
berkeman said:A typical approach is to use a PLL-based freqency synthesizer IC.
tackyattack said:I have been searching, and searching, and searching the internet on PLL devices. I can't find anything that simply explains how to make and use one. It's just too complicated for me to understand. Is there a simpler way to do it? I can recall something about using using a non-linear device to produce harmonics then using a bandpass filter to filter the correct frequency?
Averagesupernova said:Xtal oscillators around 100 Mhz will use a 3rd or 5th overtone scheme. After that the signal can be multiplied. Common is X2, X3, X5.
tackyattack said:Yeah but how do you multiply it?
berkeman said:With a PLL frequency synthesizer IC. Why are you ignoring my posts?
tackyattack said:Well, as I said in reply to your post, it was too much for me to comprehend how a PLL works. Is there an alternative?
berkeman said:No. I will try to post some helpful links tomorrow. All you have to do is Google my search terms though...
[offtopic]berkeman said:A typical approach is to use a PLL-based freqency synthesizer IC.
That is a multiplier based on a PLL, certainly. But it's a clock multiplier, and "clock" implies digital electronics and square waves. You are needing an oscillator for ham radio. Oscillators for radio involve sine waves, not square waves. Sine waves are smooth, undulating waveforms containing a single radio frequency. Square waves have sharp sides and flat tops, and contain dozens of radio frequencies, many more than you would believe. (Yes, it is possible to convert a square wave to a sinewave, but for this you need another PLL arrangement, and to get a pure sinewave is not so simple.)tackyattack said:I did some more searching and I found exactly what I need!
https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_1700720_-1
Thanks for your help!
tackyattack said:Well, as I said in reply to your post, it was too much for me to comprehend how a PLL works. Is there an alternative?
NascentOxygen said:That is a multiplier based on a PLL, certainly. But it's a clock multiplier, and "clock" implies digital electronics and square waves. You are needing an oscillator for ham radio. Oscillators for radio involve sine waves, not square waves. Sine waves are smooth, undulating waveforms containing a single radio frequency. Square waves have sharp sides and flat tops, and contain dozens of radio frequencies, many more than you would believe. (Yes, it is possible to convert a square wave to a sinewave, but for this you need another PLL arrangement, and to get a pure sinewave is not so simple.)
I think you should look for a ready-made transmitter that has been designed exactly for what you want, or at least a published circuit specific to what you need. There must be plenty of people in the same boat as yourself. I'm sure you'll find an overtone crystal oscillator designed for the bands you will be licensed to use. A crystal oscillator means that the frequency is tightly fixed so you cannot* accidently transmit outside the ham band, perhaps causing havoc. "Oscillator" means it produces a nice sine wave (providing it is working properly, of course).
Your first transmitter should be simple to understand and low-powered; it should not be your own design. RF circuits often need a lot of troubleshooting and tweaking to get them operating properly, and for this you need test equipment, patience, and an experienced mentor to guide you.
Have fun!
tackyattack said:I did some more searching and I found exactly what I need!
https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_1700720_-1
Thanks for your help!
dlgoff said:[offtopic]
Aren't there some ham class license that require crystal controlled oscillators? Been a long time since I was a novice; CW keying, crystal controlled.
[/endofftopic]
Input crystal frequency of 5 - 27 MHz
the_emi_guy said:Using a digital "clock" signal followed by 4th order filter is not uncommon in QRP designs.
You will have to design and test the filter, do you have an oscilloscope/spectrum analyzer?
Here are two examples.
http://www.amqrp.org/kits/38spcl/schematic.html
http://www.qsl.net/qrp/tx/logi-tx.htm
Those geniuses at that swharden.com link you provided paralleled outputs of a 74HC244 and sent this directly to their antenna, unterminated and unfiltered. Yikes!
the_emi_guy said:Exactly which HAM band are you targeting?
Why not use 10meters (28MHz)?
the_emi_guy said:Your balloon is TX only right? So on the ground you just need a receiver.
You can get a 10meter receiver kit for $50.
Plus, it is much easier to work at 28MHz vs. 222MHz (less worries about layout, parasitics etc.).
Since it is a balloon the antenna can be pretty long.
the_emi_guy said:Exactly which HAM band are you targeting?
Why not use 10meters (28MHz)?
davenn said:strangly enough the system on the page he linked to uses 10 metre band ... 29.xxx MHz
with an incredibly simple transmitter circuit
tackyattack --- surely one of your mates has a shortwave receiver
you are not the only ham in the area are you? don't you have an HF transceiver ?
Dave
tackyattack said:I'm a 16 year old teen, my friends aren't exactly into that kind of hobby. The closest ham group to me is too far. Actually, I'm using an SDR as my receiver. That's why the frequency range isn't too fantastic.
davenn said:OK, no probs :)
then Its good you are giving things a try, but be aware of biting off more than you can chew.
Building a VHF or UHF transmitter that has a clean output isn't a first timer starter project
Building a receiver for 29MHz would be much easier. and wouldn't cause hassles to other band users if things didnt work properly :)
Dave
vk6kro said:This might be a good time to mention that most countries have pretty strict rules about transmitting.
You don't get to choose which part of the spectrum you want to transmit on.
Even if you have a Ham licence, this would be classed as an unattended beacon and it would need to meet some strict conditions dealing with unwanted emissions.
This may vary with where you live, but you should check on your local rules. Penalties in most countries include serious fines or time in jail. So it isn't worth the trouble you could get in to.
berkeman said:@tackyattack -- vk6kro brings up some good points. Also, what are you planning on broadcasting from your module? Will it be telemetry or slow-scan video, or both? How often will you broadcast your callsign from the module?
BTW, I think it is great that you are working on such an ambitious project. If you manage to get it to work (within the legal issues), just think of the kinds of projects you will be getting to work during your college years!
Enthalpy said:This is the standard way to build a frequency doubler:
http://electriciantraining.tpub.com/14181/css/14181_95.htm
put two of them to quadruple the frequency.
A PLL does it also, but for a fixed ratio I feel it overkill.
Enthalpy said:That's it. The circuit exploits the transistor's nonlinearity.
Vbe's threshold would reduce the conduction angle below 180°, making the circuit more efficient at producing 2nd and 3rd harmonic, but the transistor's limited speed makes the waveform smoother and less harmonic-rich.
I used it up to the 5th harmonic, but this is exaggerated. The main limit is the selectivity, hence accuracy, of the output filter. A multistage filter gets any desired selectivity, but only if it pick the proper harmonic under any circumstance. As a doubler or tripler, two LC are a good value, then Q=10 uses to be more than enough.
Before chips were available, PLL were too complicated hence uncommon, and this circuit was standard practice. Still nicely simple, and it introduces less phase noise than a PLL.
Symmetric circuits, with two transistors, reduce the odd or even harmonics.