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"Paul Keinanen" wrote in message ... On Sat, 30 Oct 2004 09:59:15 -0700, "Joel Kolstad" wrote: I'm not quite following this (I don't know what a 'varactor varacitor is'?). Something like: signal -- | | -- || -- gnd Where | | is the 5pF capacitor and || is the varactor with anode facing 'left'? I'm not following how the 'back to back' configuration works. Something like this (fixed font): Vt +-+ | | | R | | +----||------+---||---+ | | | | R | | | | +----||---+------||---+ | | | | +--LLLLLLLL+LLLLLLLLL--+ | --- Gnd The cent er of the inductance L is grounded to get ground reference for the tuning voltage Vt. With a small series capacitance and a large varactor capacitance, most of the RF voltage is over the fixed capacitor. The anti-parallel structure should reduce the distortion. You need to bring the tuning voltages Vt to the varactors through separate resistors R (or through inductor resistor combinations). Paul OH3LWR Paul, The "back to back" configuration I am familiar with is like this: + Control voltage | R | +----||-----+---||---+ | | | | +--LLLLLLLL+LLLLLLLLL--+ There could also be a series cap in this configuration--except a resistor or choke would be required on one of the varactors. (no different than the one to the control line) I don't know the advantages of either config. as the RF cycle effects each diode the same way "on opposite half cycles" in either. I also don't get this talk about the filter Z. Since you'd need to Z match in/out of the filter, it seems to me the varactor voltages will be the same for any Zin/out since this will be determined by how "tightly" they are coupled into the resonant circuit and not the Zin/Zout, no? The Z match will just change the Vin/out. Steve K9DCI |
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