VCO of ranges from 925-960 and 1805-1880MHZ

[bt87]

I want to make two oVCO's ranges from 925-960 MHZ and 1805-1880 MHZ!! which oscillator you suggest me???
Colpitts,Clapp,Hartley or any other you suggest!
and why you suggest this???
please tell me i need your help?!:|
and plz provide formula of oscillator u sugest..
thanks all.

 

[radiohead]

It all comes down to the loaded Q of the resonator. With this narrow frequency range, you could consider using a coaxial resonator (Trans-Tech has a wide range), and couple the tuning varactor very lightly. You can find many examples on the web using Collpits topology.

One idea which might work: you could consider using a single VCO @ 1.8 GHz and use a divider (called prescaler at those frequencies) to generate the tunable 900 MHz. Saves you an additional varactor and synthesizer!

 

[vfone]

From provided frequency range seems that you are looking for a VCO, part of a direct up-conversion transmitter for GSM900 and DCS1800. If is a direct up-conversion, you need a VCO with a low wide-band noise, to don’t use very special TX filters.
Whatever topology you use, the quality factor of the resonant circuit is important, this including: Q of the resonator, series resistance of capacitors, series resistance of the tuning diode, the loss of printed circuit board, etc. Generally Colpitts is the most used for this kind of application.