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There exists many solutions to this problem, I am sure. How high distortion can be acceptable for your application? Are there any requirements of having a linear tuning range (meaning that for example a steering voltage of 0.1V equals 1MHz and 5.0V equals 50MHz)?
I think that many PLL-chips are able of producing this great frequency span (if only using the oscillator part of them). There are often application notes to those chips included as well in the manufacturers datasheets.
It would be a complex task to build that kind of "VCO" you need. Though it can be built as a system; for instance you may design a PLL-type VCO for some hundred MHz where the 50MHz span can easily be achieved and the output of this VCO can be downconverted with a crystal/double balanced mixer to your needed band coverage (1-50MHz).
There would be a more modern solution: that is the use of DDS chips. See for instance Analog Devices DDS family at h**p://www.analog.com/library/analogDialogue/archives/30-3/single_chip.html (* -> t) and some newer members of that line.
That would be a good solution for you. Data sheets/application notes are also downloadable from analog.com site.
I agree with Unkarc. We have just finished a classic PLL synth for an HF Tx/Rx (3-30 MHz, 1st IF OL 48-75 MHz, 1KHz step) and we need 3 IC (1 PLL, 1 VCO and 1 OPA) A lot of space, too many power supplies, expensive varicaps, coils...etc. Analog Devices AD9851 DDS can do it better; better SDFR, mHz step, one PWR supp etc...
But if you only need a VCO I should try motorola MC1648 ("the good oldie") or it's smd "new" version MC12148. Maxim's wideband VCOs are another alternative but keep in your mind you have to face with two "words": coils (Coilcraft is a good choice) and varicaps (another world)
PS: I forgot Minicircuits' VCOs (no external comp. needed)
<font size=-1>[ This Message was edited by: Chinasky on 2002-02-15 12:04 ]</font>
many DDS have internal (fixed) "sine" lookup table but other can be programmed externally making so an Arbitrary waveform generator. Setting up tables for canonical waveforms is almost an easy task.
Take a look to Harris and Qualcomm prods too.
Hope this will be helpful.