el cheapo oscillator

[dannyf]

Experimenting the oscillator on this link: http://www.b-kainka.de/bastel3.htm

and decided to simplified it to just 5 parts: 2 transistors, 1 resistor, 1 inductor and 1 capacitor.

Simulated well so I built one.

[dannyf]

Here it is, living on a breadboard.

The transistors are lowly 2n5401, and the inductor came from a dead cfl lamp. I used two 1k resistors in parallel in the base.

[dannyf]

What it looks on the scope, as is.

120Khz makes it quite interesting. the inductor is about 20uh.

[dannyf]

This thing oscillators without that capacitor there - distributed parameters I guess - at 1.7Mhz.

[dannyf]

The amplitude is fairly constant from 120Khz to 1.7Khz: 60mv Vpp.

Current consumption is 4ma @ 5v and 2ma @ 2.5v. Reasonably frugal.

You can probably make it go higher with a better layout and faster transistors: the 2n5401 isn't known for its speed.

[dannyf]

With simpler wire routing, I got it to work at 30+Mhz - the inductor was a simple 3" long copper wire.

[dannyf]

77Mhz with a pair of 3906s.

[dom0]

Unloaded emitter followers also make great UHF oscillators. Although, not very stable ones.

[paulie]

I was surprised to see most of the 2.4ghz and higher oscillator circuits were 2 transistor. I  have some 11ghz bipolars and 2-24pf variables in my junk box and would love to build a microwave range GDO. I thought single transistor was the way to go but maybe not.

[djacobow]

77Mhz with a pair of 3906s.

Did you reverse the circuit?

[SeanB]

Gunn diode you really only have one component, and it is not even a device with any PN junctions in it. You do need a tuned conductive box to house it, which determines the resonant frequency though.

Almost any power Mosfet ( VN10KM) can make a very low component count VHF oscillator, just use long wires on the leads and keep them close to each other.

[tszaboo]

I've got 77MHz from a SN74AUP3G04 ala ring oscillator. I actually wonder a single 74x00 can do in terms of stability. Maybe I'll hook up one to a counter one day.

[SeanB]

IIRC they go up to about 40MHz, though you can tune them using the supply voltage somewhat. CMOS inverters do have a much lower frequency, but a lot more linear voltage control. I have seen a Frequency-voltage converter that used a CMOS inverter supply current as the conversion, as it is almost linear with applied frequency with no load.

[dannyf]

Did you reverse the circuit?

I hope so. I was actually running on 2n5551 (npn). 2n5401 is pnp.

Point-to-point construction probably will allow it to go to the FM band.

[dom0]

IIRC they go up to about 40MHz, though you can tune them using the supply voltage somewhat. CMOS inverters do have a much lower frequency, but a lot more linear voltage control. I have seen a Frequency-voltage converter that used a CMOS inverter supply current as the conversion, as it is almost linear with applied frequency with no load.

I think I saw that one too... must have been either a Linear or TI appnote... not sure which...

[PA0PBZ]

Just tried with 2 BFR91's head to tail and a little U as the coil. Easy 400MHz and probably well over 1GHz with some cutting.

[Zero999]

Awhile ago I built one based on this schematic:


http://www.next.gr/rf/uhf-circuits/simple-uhf-oscillator-l11838.html

Except I used SMT inductors and capacitors, a small air core inductor, consisting of some enamel wire wrapped round a PCB drill bit to form it and the BFT92. It was assembled on a very tiny piece of stripboard. It worked to over 1GHz and would probably have gone higher but the frequency counter topped out at 1.3GHz.

[dannyf]

Built one from a pair of s9018. Over 130Mhz.

edit: picture added.

[paulie]

probably have gone higher but the frequency counter topped out at 1.3GHz.

Singles ahead by TWO LENGTHS. (1300 vs 400 mhz) And there goes SWIFTY!

[dannyf]

Implementing this on a dual gate mosfet would be interesting.

[babysitter]

Yeah, I saw the opening post oscillator used for Respiratory inductance plethysmography before - basically the inductor was wound around a person and the breathing movement retuned the oscillator. Also a nice method to detect if someone is sitting on a chair or lying in a bed

Project idea for the trainee pops up - build such an oscillator and see what you can do with it, employing different coils etc.

[dannyf]

If two transistors are too much for you, here is a one-transistor version:

[dannyf]

Living on a breadboard.

[dannyf]

oscillating at 500Khz happily.

[dannyf]

The oscillator easily starts up in oscillation and isn't picky about transistors - S9018 (1.1Ghz) works just as well as a 2n5551 (150Mhz).

Higher resistor values (lower collector current) give better sine waves.