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500Mhz Oscillator

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Madgyver

Wed Mar 15 2006, 03:22PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

Hi there.
Is there anyway to make a 500Mhz Oscillator, which should be stabelised by a crystal? There should be some option to callibrate too, but that feature isn't very important.

Any easy ways?

[mod edit] Fixed title spelling to aid in searches.

WaveRider

Wed Mar 15 2006, 03:37PM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

Other than using a PLL to make a synthesizer, you can use frequency multiplier stages (usually doublers and triplers) to multiply the frequency of a crystal time-base. I once built a transverter that required a 560MHz local oscillator... I used a multiplier chain of 7x, 4x and 2x multipliers to get 560MHz from a 10MHz crystal oscillator. Note that this method yields a fixed frequency.
If you want variable frequency, a PLL synthesizer or a DDS synthesizer with frequency multiplication may be the way to go...

Hope this helps!

Madgyver

Wed Mar 15 2006, 03:49PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

This sounds interesting. Thx. what would such a multiplier look like? I mean, is it avalable as a single chip solution or do I have to build them seperatly?

Carbon_Rod

Thu Mar 16 2006, 07:29AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
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Posts: 1155

Or some sort of simple VCO... depends what kind of signal you want.
Simple vco unit example (google should have more of these):

The noise problems above 200MHz can get tricky to find. But I like the 2SC2369 as a cheap UHF npn high frequency transistor (by far not the greatest for transmitter design etc. they are supposed to be ok up to 1GHz but I found the NEC brand db roll off tends to fall short of specifications.)

The weird thing about crystals is the cheap ones can have high frequency harmonics most people tend to ignore/filter. IIRC there are a few designs that use this property to get higher frequency outputs. Some guy apparently built a low power â€œjammerâ€ with a few parts scavenged off an old motherboard -- I never did look into what kind of signal the design produces.

If stability is an issue the previously mentioned PLL with an onboard crystal oven can give you better results. Note as the crystal starts to age the frequency will shift slightly. These days most people have compensated for the errors at the software level knowing the decay curve over the lifespan of the circuit. Without this some watches could be +-0.7 seconds or more off each year even with the better tuning fork cut low frequency crystals.

Cheers,

WaveRider

Thu Mar 16 2006, 09:05AM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

Hi Madgyver..
Have a look at my project writeup here

. I describe the multiplier chain. A multiplier is, simply put, an amplifier biased and driven such that the output is rich in harmonics. You then use a filter tuned to the desired harmonic...

Madgyver

Thu Mar 16 2006, 05:25PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

WaveRider wrote ...

Hi Madgyver..
Have a look at my project writeup here

. I describe the multiplier chain. A multiplier is, simply put, an amplifier biased and driven such that the output is rich in harmonics. You then use a filter tuned to the desired harmonic...

Ah very interesting thank you. I guess I understand it better now.

Carbon_Rod wrote ...

Or some sort of simple VCO... depends what kind of signal you want.
Simple vco unit example (google should have more of these):

..snap..

I think the VCO is the way to go, I already found a supllier in the 450Mhz range, which is good enough for me.

THX a lot.

HV Enthusiast

Thu Mar 16 2006, 06:00PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Minicircuits has a lot of low-cost oscillators in the range you are looking at . . .

www.minicircuits.com

WaveRider

Fri Mar 17 2006, 09:05AM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

And if you want crystal-like stability, you will need to use the VCO with a PLL like this one...

Madgyver

Fri Mar 17 2006, 06:09PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

Wow, that looks promising. THX

HV Enthusiast

Fri Mar 17 2006, 08:37PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Madgyver wrote ...

Wow, that looks promising. THX

Better read the datasheet first. From first looks, you'll need a lot of interfacing to get this VCO chip to work including a serial input interface.

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