How do you multiply the frequency of an oscillator?

[tackyattack]

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]

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?

A typical approach is to use a PLL-based freqency synthesizer IC.

 

[tackyattack]

A typical approach is to use a PLL-based freqency synthesizer IC.

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]

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.

 

[berkeman]

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?

Please try a bit harder. I gave you the search terms to use. If you need spoon feeding, I can give you direct links. Sorry to be harsh, but it's not that hard.

 

[tackyattack]

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.

Yeah but how do you multiply it?

 

[berkeman]

Yeah but how do you multiply it?

With a PLL frequency synthesizer IC. Why are you ignoring my posts?

 

[tackyattack]

With a PLL frequency synthesizer IC. Why are you ignoring my posts?

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]

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?

No. I will try to post some helpful links tomorrow. All you have to do is Google my search terms though...

 

[tackyattack]

No. I will try to post some helpful links tomorrow. All you have to do is Google my search terms though...

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]

A typical approach is to use a PLL-based freqency synthesizer IC.

[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]

 

[NascentOxygen]

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!

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!

 

[vk6kro]

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?

Any waveform that is not a sine wave contains harmonics of the fundamental frequency. A 1000 Hz signal that is not a sine wave contains exact multiples of 1000 Hz.

So, to produce multiples of a sinewave's frequency, you just have to distort it.

A square wave contains the fundamental frequency plus odd harmonics. Other waveforms contain different proportions of odd and even harmonics.

If you took a transistor with a tuned circuit resonant at 100 MHz in the collector and applied a large 50 MHz sine wave to the base, the result would be 100 MHz output from the collector.
Simple parallel tuned circuits are not perfect, though, and there would also be detectable signals at 50, 150, 200, 250 (and so on) MHz.

There are other types of frequency multiplier.
A full wave rectifier produces large amounts of second harmonic.
Diodes whose capacitance varies with voltage, but in a non linear manner, can also be used to generate harmonics.

 

[tackyattack]

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!

A ready-made transmitter would be the right choice, but one good enough for my purposes will be too expensive. I am going to attach the transmitter to a high altitude balloon so I was hoping to make it myself. I won't be getting the transmitter back so a disposable module is what I am trying to achieve. This is what I am trying to copy: http://www.swharden.com/blog/2010-07-14-high-altitude-balloon-transmitter/
But the can oscillator he uses is below the frequency range of my base station. I thought it would be simple enough to find a VHF can oscillator, but it's not. And after learning about these transmitters I found out that, as you mentioned, square waves are a big no-no.

Here is what I was going to do: https://www.sparkfun.com/products/9261 + https://www.sparkfun.com/products/9089 + http://www.radioshack.com/product/index.jsp?productId=2062616

 

[berkeman]

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!

[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]

Hi Don,

Frequency synthesizers are crystal controlled. From the datasheet linked to in tacky's post:

Input crystal frequency of 5 - 27 MHz

You choose the input crystal frequency and the multiplier-divider ratios in the synthesizer to give you the desired output frequency.

Although, as correctly pointed out by others, the output of the synthesizer is digital, and needs filtering to be used as the TX carrier waveform.

 

[the_emi_guy]

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!

 

[tackyattack]

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!

Interesting. I do have an oscilloscope but I don't think it would be capable of reading 200 mhz signals.

 

[the_emi_guy]

Exactly which HAM band are you targeting?

Why not use 10meters (28MHz)?

 

[tackyattack]

Exactly which HAM band are you targeting?

Why not use 10meters (28MHz)?

1.25 meters. I would use 10 meters, but my receiver can only receive between 52 - 2200 MHz.

 

[the_emi_guy]

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.

 

[tackyattack]

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.

I already have a setup that I put money into though. :(
Would a $50 kit even be enough to receive low power signals from that far?

 

[the_emi_guy]

What is the receive sensitivity of your receiver at 52MHz?

I'm guessing that even cheap kits give you < 1uV at 28MHz.

(Do you still have the receipts?)

 

[davenn]

Exactly which HAM band are you targeting?

Why not use 10meters (28MHz)?

strangely 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]

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

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]

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.

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]

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]

@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!

 

[tackyattack]

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

Thanks, that makes sense! I guess I should probably stick with pre-made transmitters for the VHF and beyond frequencies. It's too bad building a disposable VHF module is nearly impossible! Maybe once I have some low frequency transmitter experience under my belt I can safely move up to the higher bands. Or maybe I should just get a lower frequency receiver ;)

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.

Right. I'll make sure to look into the laws for my areas more carefully. I have learned a bit about them for my type of project, but probably not enough. Thanks for the warning! I do have one question: isn't there a point above the Earth that radio laws no longer apply? There has to be some height where they are no longer valid because it's not like there are laws for radio communications on the moon. Right?

@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!

I plan on transmitting temperature and pressure telemetry through a kind of OOK binary transmission. As far as my callsign, I plan on broadcasting it at the end of each transmission. That would be the easiest.

Thank you for your kind words! I am very excited for college!

 

[Enthalpy]

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.

 

[tackyattack]

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.

Wow, that is very simple! So adding more than two would cause the signal to diminish to nearly nothing. But, what if you amplified before adding into the next multiplier? Would there be a point that too much noise is introduced?