VCO Seiler 80Mhz-300Mhz

Posted on Feb 4, 2014

VCO is definitely useful in so many RF projects, wide band Ghz VCO get more concern than VHF/UHF VCO. here is a Manhattan Island Pad construction for VHF VCO, low to 88Mhz and up to around 300Mhz. Here is the schematic, a Seiler oscillator, Voltage controlled via a BB910, from 0V to 15V get 88Mhz to 180Mhz covered. My linearity ramp genarator out

VCO Seiler 80Mhz-300Mhz
Click here to download the full size of the above Circuit.

put sawtooth ramp from about 1. 5V to 13. 5V, then cover 100Mhz to 170Mhz range. All critical component in above pictures is given a range to try, and my construction use: C5:472, C4:22p C7:30p Air coil: 0. 8mm coper wire round diameter 5mm, 4 turn. it`s worthy to point out : Island pad with a ground plane lead make up a small capacitor, i use 0. 8mm Pad for easy soldering each such pad had about 3pF, include this cap for design your PCB, or use single side copper clad board. the following image is not output from the oscillator, it`s come from a frequency meter, divide input frequency by 32. I had 100M Oscilloscope, for frequency around 100M and above it`s just use to view the Oscillation envelope All above test use transistor 2sc9018, which GBW (Ft) is 1Ghz. This circuit use common Collector Amplifier, a little poor performance than common base. so if you try let it work above 180Mhz, suggestion use transistor that GBW is above 3Ghz (worth to try). and i put a 2SC3355, which GBW 6. 5Ghz, that work well up to 280Mhz. output power drop quick when work frequency is growth, this is not so wide band VCO, but from 88Mhz up to 300Mhz is also impressive me. depend your varactor, for common case 2:1 tune range is easy to achieve. and stability is about 10-5. (10khz per second, no shield, no special consideration for stability. ) the transistor work at very high point(so much current flow to emitter ). and at such condition, the...

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