Challenge Thread: The fastest breadboard oscillator on the mudball

[SiliconToaster]

How fast can a 2N3904 go?

Here it is, a 2N3904 in a "colpits" oscillator running at over 460MHz. 
Not too bad for a transistor with a 300Mhz transition frequency.

The schematic is really simple, the BJT is biased in a common base configuration and it relies on the breadboard parasitics to get into oscillation.




As you can see the signal is coupled into the oscilloscope probe via the breadboard capacitance, a direct connection is too much load for the circuit.




For a moment I was able to get it running at 505MHz, I think that's the limit for the 2N3904. Next step is to get a better transistor.

[SilverSolder]

How fast can a 2N3904 go?

Here it is, a 2N3904 in a "colpits" oscillator running at over 460MHz. 
Not too bad for a transistor with a 300Mhz transition frequency.

The schematic is really simple, the BJT is biased in a common base configuration and it relies on the breadboard parasitics to get into oscillation.
(Attachment Link)

(Attachment Link)

As you can see the signal is coupled into the oscilloscope probe via the breadboard capacitance, a direct connection is too much load for the circuit.
(Attachment Link)

(Attachment Link)

For a moment I was able to get it running at 505MHz, I think that's the limit for the 2N3904. Next step is to get a better transistor.

Very cool!  -  How does the oscillator actually work?  I don't see a feedback path...

[0culus]

How fast can a 2N3904 go?

Here it is, a 2N3904 in a "colpits" oscillator running at over 460MHz. 
Not too bad for a transistor with a 300Mhz transition frequency.

The schematic is really simple, the BJT is biased in a common base configuration and it relies on the breadboard parasitics to get into oscillation.
(Attachment Link)

(Attachment Link)

As you can see the signal is coupled into the oscilloscope probe via the breadboard capacitance, a direct connection is too much load for the circuit.
(Attachment Link)

(Attachment Link)

For a moment I was able to get it running at 505MHz, I think that's the limit for the 2N3904. Next step is to get a better transistor.

Neat circuit. I tried reproducing it with a 2N2222A but so far have "only" achieved a 358 MHz fundamental. I need to play around with the inductor I think...I've been experimenting with winding my own with some very fine gauge wire I had on hand. I'll share some pics once I've worked with it.

To segue into faster circuits, I found a couple of mixers on minicircuits that should work for my needs. I will soon order them and some high speed transistors. 

[0culus]

How fast can a 2N3904 go?

Here it is, a 2N3904 in a "colpits" oscillator running at over 460MHz. 
Not too bad for a transistor with a 300Mhz transition frequency.

The schematic is really simple, the BJT is biased in a common base configuration and it relies on the breadboard parasitics to get into oscillation.
(Attachment Link)

(Attachment Link)

As you can see the signal is coupled into the oscilloscope probe via the breadboard capacitance, a direct connection is too much load for the circuit.
(Attachment Link)

(Attachment Link)

For a moment I was able to get it running at 505MHz, I think that's the limit for the 2N3904. Next step is to get a better transistor.

Neat circuit. I tried reproducing it with a 2N2222A but so far have "only" achieved a 358 MHz fundamental. I need to play around with the inductor I think...I've been experimenting with winding my own with some very fine gauge wire I had on hand. I'll share some pics once I've worked with it.

To segue into faster circuits, I found a couple of mixers on minicircuits that should work for my needs. I will soon order them and some high speed transistors. 

OK, so I made some modifications to your circuit. I added some extra bypass filtering on the power supply, and I substantially reduced the capacitors down to 4.7pF. I also turned the wick way up, and worked my way up to 25V, drawing about 33mA. I have achieved a very nice stability at about 444.3 MHz. I have a few other things in mind to try as well. Also FWIW, the 7104 trace is overexposed by the camera's sensitivity to the phosphor. It is *not* that bright in person!

[0culus]

One more update to this modification of SiliconToaster's circuit tonight: I found a few 1 pF ceramic caps in my stuff. After much experimenting with adjusting the inductor and the cap, I happened upon this configuration. Turns out, trimming off the legs of the 1pF cap stops the circuit from oscillating. So I left it to stand tall and bask in the glory of parasitics.  It is so sensitive now that I cannot even bring a near field probe near the circuit without completely detuning it. So I grabbed the spectrum analyzer data while carefully holding the probe a distance away.

[SilverSolder]

This is starting to look pretty fast!

I still don't get how the oscillator in the diagram oscillates without a feedback path.  Is there a parasitic path somewhere that I'm missing? 

[0culus]

This is starting to look pretty fast!

I still don't get how the oscillator in the diagram oscillates without a feedback path.  Is there a parasitic path somewhere that I'm missing?

Yes, i believe it is depending on parasitic capacitance from the breadboard to form the full tank circuit that sets the frequency.

[SiliconToaster]

This is starting to look pretty fast!

I still don't get how the oscillator in the diagram oscillates without a feedback path.  Is there a parasitic path somewhere that I'm missing? 

No idea of where the feedback path is. As 0culus said, it's a combination of the breadboard and transistor parasitic capacitance.
At these frequencies every wire becomes an inductor and every cap becomes a resonant circuit with it's own resonant frequency that varies with the length of it's legs. 

I tried to exploit the parasitics even more, so I took out the coil and replaced with three wire links in parallel to reduce the inductance.
I also raised the voltage from 12V to 20V.
Now it's running at 536MHz. 







 

[KE5FX]

This is starting to look pretty fast!

I still don't get how the oscillator in the diagram oscillates without a feedback path.  Is there a parasitic path somewhere that I'm missing?

Miller capacitance between  base and collector would be my initial hand-wavy guess.  I don't think it's the breadboard strays, but could be wrong.

[herc]

i just stumbled upon this paper talking about THz Oscillators: https://hangroup.mit.edu/wp-content/uploads/2019/03/IEEE_Filling_the_Gap_Published.pdf

did someone here experimented with spark gaps ? what would happen if i would put sparks onto a simple biquad-antenna,  let's say for the 2.4 GHz ? how broad, how dirty would the spectrum be ?

[mnementh]

This is starting to look pretty fast! I still don't get how the oscillator in the diagram oscillates without a feedback path.  Is there a parasitic path somewhere that I'm missing? 

   No idea of where the feedback path is. As 0culus said, it's a combination of the breadboard and transistor parasitic capacitance.

At these frequencies every wire becomes an inductor and every cap becomes a resonant circuit with it's own resonant frequency that varies with the length of it's legs. 

I tried to exploit the parasitics even more, so I took out the coil and replaced with three wire links in parallel to reduce the inductance. I also raised the voltage from 12V to 20V.
Now it's running at 536MHz. 

Now... now you're starting to get into the same realm of Black Magic as this thing:

joe, OTOH... This is all like watching Master Po and young Kwai Chang Caine discussing discipline in the rock garden... 

mnem
Carry on, please! 

[joeqsmith]

A package arrived today and it's time to get serious.. 

The cheap mechanical trimmer is out.  It would be very helpful to have but the breadboard needs to be mounted to a metal plate with a real stage mounted on the plate as well.  It seems like it may fall into the realm of modifying the breadboard.   Currently, this is a job for tweezers, very sharp dykes and the microscope. 

OP, can we use some sort of off board mechanical positioning system as I describe above?   The breadboard would need to be hard bolted to the plate and the stage would be something like this but smaller:
https://www.ebay.com/itm/Newport-562-LH-XYZ-Stage-ULTRAlign-with-13mm-travel-micrometers/293255578226?hash=item4447650272:g:fcsAAOSwt95dkpHw

I have no plans now to use Ferrite, but if someone wanted to use it, would there be any special provisions?  It seems like using a continuous wire to make an air coil is one thing but filling it with Ferrite may be another.   

Can we use the Kapton tape as an insulator as I have shown?   There really isn't a performance gain, at least the way I intend to use it.  It's really just for added protection.  Like the Ferrite, it's now more than just some bent up wire.   See attached post for detaileds pictures:
https://www.eevblog.com/forum/projects/challenge-thread-the-fastest-breadboard-oscillator-on-the-mudball/msg3098642/#msg3098642

joe, OTOH... This is all like watching Master Po and young Kwai Chang Caine discussing discipline in the rock garden... 

Playing with high speed parts is a lot of fun.  You should join the fun.

[BreakingOhmsLaw]

@Joe:
Breadboard: Fixing it is fine, just don't damage or modify it. It should be reversible to a pristine breadboard again.
Kapton: Yes, all that's going to do is act as an dielectric in a ghetto capacitor, so that's covered by rules 5 & 8.
Ferrite: Yes, Rule 5 & 8 again.
Positioning jig: Absolutely, if that's what it takes. Not sure if a lump of metal near your circuit is going to give you trouble.

@SiliconToaster:
Great entry! I will update first post to reflect you as runner-up! Keep it up!

[cj]

This circuit won't break the record but has some 'black magic' to it.
It has only two components a BFR91A transistor and 10k resistor.

[joeqsmith]

This circuit won't break the record but has some 'black magic' to it.
It has only two components a BFR91A transistor and 10k resistor.

That's the old SA I used to have, except maybe the A version.  Very nice!  Also, welcome to the 1GHz+ club!!

[BreakingOhmsLaw]

This circuit won't break the record but has some 'black magic' to it.
It has only two components a BFR91A transistor and 10k resistor.

And two creafully selected and hand-tuned marker pins! 

[0culus]

That was my first SA too...I got it for a song and the guy didn't pack it...like at all. Miraculously it survived shipping. Tough bastard.

@joe, can't wait to see what you cook up! I'm going to order stuff soon. 

[joeqsmith]

@Joe:
Breadboard: Fixing it is fine, just don't damage or modify it. It should be reversible to a pristine breadboard again.
Kapton: Yes, all that's going to do is act as an dielectric in a ghetto capacitor, so that's covered by rules 5 & 8.
Ferrite: Yes, Rule 5 & 8 again.
Positioning jig: Absolutely, if that's what it takes. Not sure if a lump of metal near your circuit is going to give you trouble.

I've been soldering to the plugged in wires, melting the breadboard every so often.   Then there was a lockup meltdown... Sadly this old breadboard will never be pristine again.       

Thanks for clearing up my questions.

I plan to change over to using a small 3XAA battery pack.  I worry that one swipe with Tim's tail (our dog) on the power leads will end it.   

Now if LeCroy would just send me a 40GHz scope.   

[cj]

For who thinks the marker pins are part of the 'black magic' NOPE it works also without them.


@joe : thanks for welcoming me to the 1GHz+ club.
The 8569B is a nice but old SA and goes up to 22GHz.

[ogden]

For who thinks the marker pins are part of the 'black magic' NOPE it works also without them.

It shall be noted that your >1GHz breadboard oscillator fully follows rule #3. Congrats!

[0culus]

@Joe:
Breadboard: Fixing it is fine, just don't damage or modify it. It should be reversible to a pristine breadboard again.
Kapton: Yes, all that's going to do is act as an dielectric in a ghetto capacitor, so that's covered by rules 5 & 8.
Ferrite: Yes, Rule 5 & 8 again.
Positioning jig: Absolutely, if that's what it takes. Not sure if a lump of metal near your circuit is going to give you trouble.

I've been soldering to the plugged in wires, melting the breadboard every so often.   Then there was a lockup meltdown... Sadly this old breadboard will never be pristine again.       

Thanks for clearing up my questions.

I plan to change over to using a small 3XAA battery pack.  I worry that one swipe with Tim's tail (our dog) on the power leads will end it.   

Now if LeCroy would just send me a 40GHz scope.   

Fortunately my cats have been (so far, knock on wood) leaving these experiments alone. 

I'd like a 40 Ghz scope too; I have plenty of monopoly dollars! 

Anyway, I was able to hit 660 MHz using the same circuit but a faster 1 GHz transistor I found in my box of toys, and adding a high tech "ferrite" (really the tip of a small screwdriver  ) to the inductor loop. I want to experiment further so I won't share until I've extracted every last MHz out of it.

[joeqsmith]

I really figured the cat took that knob from my scope.     She sleeps most of the time and doesn't cause much trouble.

I'm in the same boat, wasn't born with a silver spoon and no one accepts my funny money.       Maybe I could offer LeCroy exclusive advertisement.... Nah... that's sounding too much like work....   

I added an LED to the battery pack to try and remind be to turn it off.  Also shown is the new oscillator on the right fitted with one of the new transistors.  At least I can afford the parts.     Between the two oscillators is my chip of ferrite.  All sitting on the freq counter which is apart while I am trying to sort out how fast I can actually drive it. 

I see some gains with the ferrite but keeping things mechanically stable has been a problem.  Too bad the Revlon clear didn't work. 

I want to experiment further so I won't share until I've extracted every last MHz out of it.

      With Trash and now CJ catching up fast, it's time for you to get some better parts.  There's always room for more in the 1GHz+ club!   

[herc]

@cj: thats a crazy oscillator. if this transistor still oscillates, even though there is the breadboard capacitance all over the place, (and with that weird "shortcut" inductor / resonator / between collector and base), how can you ever built a non-oscillating amplifier with that thing   ?!?

[cj]

The circuit is basically a Pierce oscillator.
The base and collector are shorted (DC) but for this transistor as with many others Vce_saturated < Vbe.
With the 10k resistor the bias voltage is Vbe so the collector isn’t saturated yet and therefore the transistor works normally albeit at a low voltage.
I’ve tested this circuit at 3V and works fine. At this voltage the total power dissipation is about 0.7mW and the generated RF power is a small fraction of that.
If you want to build a non-oscillating amplifier with these types of transistors don’t use a breadboard.

[TheUnnamedNewbie]

I've been thinking if you could use a gunn diode and use the walls of two slots in the breadboard like a waveguide. Add a short a bit further back between the two same walls to make your resonant section of waveguide. Point horn antenna at it to measure frequency.