I agree, incorrect, at the moment you have a DC path from the top of the varicap to ground through the coil, so it will never vary from maximum capacitance, and you may well kill the oscillation as well.
Depending on the circuit, 1n or 10n will be OK. you dont want it too small, otherwise the effective varicap capacitance will be affected by the series capacitance of the blocking capacitor.
Yes your right L1 will short your dc to ground and the 47k will load the osc and possibly stop it, all previously posted.
Its possible that the inductor could be of suffciently high dc resistance not to affect the tuning voltage (saturation might then be problem though), but very unlikely to be high enough not to be affected by the 47k resistor, and even then the oscillator would be uneccesarily loaded
The last month or so I have been doing quite a bit with varicaps that go to 500p
I replaced a the crappy polyvaricon in a simple "antenna analyser" with two back to back, and still had enough to reduce the bands from 4 to 3 and with a 10 turn pot, very nice to use. Made a sweep generator that will give me 1024 steps between two preset frequencies using a pic and a resistor da converter to give me a rough idea of filter bandpass, made an effective SW receiver, again ten turn pot and switched presets to create "bands", and probably the most useful one was a variable bandwidth IF filter.
I've a frequency standard that tunes to radio4, it uses a 1n4007 as a varicap, that particular diode works well as a varicap, the capacitance of the diode is adjusted using dc to 'pull' the frequency of a crystal osc to sync up with the radio 4 signal using a very simple pll.
I've a frequency standard that tunes to radio4, it uses a 1n4007 as a varicap, that particular diode works well as a varicap, the capacitance of the diode is adjusted using dc to 'pull' the frequency of a crystal osc to sync up with the radio 4 signal using a very simple pll.
Red LEDs are good to. Light has been shown to have minimal effect, most are enclosed anyway, and a tin of black spray paint would eliminate any undesirable effect.
I think the curve on the LED is more usable in some cases. The rectifier diode has most of its range in the first couple of volts, the LED has the same range over the first 6 volts. Neither are anywhere near linear, so I won't use that as a description.