AM Radio Design Log

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Jan - then you do not know the Vacker oscillator either ;-)

E.g. Why do engines have names V8, Stirling Engine, Jet Engine and so on.

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My presumption is that all variable LC oscillators ought to be using Vacker design to correctly maintain oscillation combined with low feedback and amplitude - over a small - or especially wide frequency variation.

With all the electronic made in the last 30 years, why has no one found this design (again)? Why has no one been educated about this oscillator?

The Vackar VFO oscillator:

Quote: "... Jiri Vackar [Ji?í Vacká?] invented his VFO oscillator during late 40s. It is probably the most stable VFO oscillator known. Thanks George! ... The frequency tuning range is above 2.5, not observable in any other type of oscillator. The Coupling ratio is fixed; typical range is 1:4 up to 1:9. [] The tuning is provided independently of coupling. Transistor's parametric variables are isolated from the resonator. The transistor input is not overloaded as Clapp or other circuits. ... The stability is close to XO. ... Ordinary oscillator has poor tuning range, the output voltage swing is unstable, and the frequency stability is poor as well. The industry tries hard to make its sale pitch, to replace single oscillator with 50 ICs, digital dividers, approximation registers, thermostats, and other junk. Now what? ... The best regulator of all times is maybe the LM723. [really :-)] ... The VFO is better solution than the AD9850,AD9891 DDS - direct digital synthesizer chip. ... Do you want to spend time calling around and dealing with ten weeks lead time? An old cap from an old TV tuner can help to solve your problem. The treasures are around you. ..."

Scanning of original paper:

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A regenerative receiver ought to be easier to tune with Vacker design. Why has anyone not thought of that - assuming no one did - please correct me if I am wrong.

Glenn

On 20/07/13 22.10, Jan Panteltje wrote: ...

White Hockey puck oscillators...

Named after their inventor Dr White-Hockey? ;)

Quote: "... Specifically, Vacká? found that forward transconductance varied as ?3 for the Clapp oscillator, as 1/? for the Seiler oscillator, and as ?/Q for his design, where the Q factor of the coil (L1) increases with ?. ..."

/Glenn

On a sunny day (Sun, 21 Jul 2013 09:05:02 +0200) it happened Glenn wrote in :

Right, the fun is the 'pucks'(been a while since I played hockey) are not really mechanicaly or electrically ? connected to anything. They are EM coupled however to 2 nearby mircro strips, and one oscillates at 9.75 GHz (the big one), and the other at 10.6 GHz.

On a sunny day (Sat, 20 Jul 2013 14:18:42 -0700) it happened Fred Abse wrote in :

See my reply to Glenn. or

On a sunny day (Sat, 20 Jul 2013 20:42:56 -0500) it happened John S wrote in :

Yes good point. I guess I am no discus (sers).

Actually, apart from all the fun, lately the following (deep) thought pooped (eeeh Freudian? [1]), should be popped LOL), up in my mind: There are those who read a book and get the story. There are those who spell it word by word and argue about the words, those are the pundits of today. And there are those who write the stories, and there are those who live the stories.

[1] Maybe not 'o' is next to 'p'.

On a sunny day (Sat, 20 Jul 2013 21:02:16 -0500) it happened John S wrote in :

Right, I had that problem several times, perhaps ceramic caps dissipate away energy by mechanical vibration.

I often write 'poly' next to tuning caps, in one of those voltage converters the ceramic caps actually got hot. Was way below their specified operating voltage.

On a sunny day (Sun, 21 Jul 2013 09:00:23 +0200) it happened Glenn wrote in :

Right, did not see that one before. I have used that circuit I drew for VCO at 1.5 MHz, and it is really really stable (wit hteh right caps). I guess stable enough for SSB.

Of course the 1.5M was added to some multiplied xtal to listen to the 21 MHz band. It was sure more stable than my Trio tube short wave receiver tha tI needed to keep the hands on the VFO to keep picth with SSB...

Yes, to a point, we call this thing 'oscillator' remember, do you know how many types of jet engines there are? Maybe not as many as oscillators, but really close ;-)

Well these days it is all about integration, silicon is very cheap. It allows also very small structures that work in the THz range. Dividing down is digital and takes little silicon space, so there is a solution, make any frequency step you like. The need for VCO's has gradually decreased I think.

Regenerative receivers radiate a lot usually, interfering with other receivers listening for the same frequency. If you look at stuff like the RTL DVB-T sticks (rtl_sdr as used for software radio), I can only be amazed that thet what once was a big cabinet full of capacitors, inductors, tubes, and 'do not breathe while using this' signs, is now the size of a postage stamp with way better specs, and a zilions times the power requirement. Elonix 4000 tuner chip...

1940 tech was huge.

On a sunny day (Sat, 20 Jul 2013 14:08:42 -0700 (PDT)) it happened "M. Hamed" wrote in :

OK, now things are sinking, you missed an opportunity to CALCULATE the capaciatnce of your meter.

You had L, C, and frequency f. You added the meter, and found now a lower frequency f2. L has not changed, so now you can calculate C meter (plus hands etc). No need to even measure it.

You talked about where to put the tap on the coil, and noticed it made little difference. Do you realize that sets the gain?

tuned cicuit -> amplifier -> feedback network - | | | | --------------------- 1. If it is >> 1 it will oscillate anyways, maybe not so nice as yo uwoudl like for very high gains.

And that is how simple it is.

I remember I had to calcualte those freaking things, there is

's_theorem 's_circuit_laws

and a few more.

These YIG-stones is also smart - great oscillator and filter balls - but not named after any human? They are also EM coupled:

Used in elder quality spectrum analyzers.

Wouldn't surprise me. Most of the High K ceramic dielectrics are piezoelectric in nature. They also make physically resonant filters with the same materials.

?-)

On 21/07/13 10.39, Jan Panteltje wrote: ...

The reason is high ESR. Even ce-capacitors are divided in "normal"-ESR and low-ESR.

In window "Applications" you can choose SMPS filtering:

Capacitor Values: Don?t Believe the Label:

Therefore some ceramic types can be used for measuring voltage or temperature, because the capacitance vary.

On a sunny day (Sun, 21 Jul 2013 14:08:54 +0200) it happened Glenn wrote in :

Good data!

I had, just a few weeks ago, used ceramic SMD 100 nF caps to decouple some tuning voltage, well I _tried_, until I noticed that any movement of the board threw my 1.5 GHz VCO way of frequency, in the end just blowing against the board, the sound of air hitting it, was enough to send the VCO all over the place. Replaced those caps with 1 uF electrolytics... problem gone.

-- 220k --- VCO | | === | ///

I am sure if I had fed the output into a FM demodulator it would have made good audio. Hey, an idea: cheap ceramic microphones, re-branded caps... (China will pick up now ;-) ).

SMDs are specifically sensitive as any board bending puts huge forces on those.

Shouldn't that be "Vackar"?

-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Yes. That was done on purpose. I remembered reading somewhere that coupling is not needed (I think it was in Hayward's Introduction to RF Design).

It was something I wanted to try and it saves me an extra toroid. Wounding both inductors on the same toroid would have been essentially the same.

Thanks John. I appreciate the encouragement.

From my readings, capacitor low Q is usually not an issue up to high frequencies. Before that the inductor Q is more important. I am compelled to ask at which frequencies was this a problem to you?

The discussion about capacitors reminded me of a good article I read a few weeks back on EDN:

It has mention of piezoelectric effects and also variations with voltage which are often not specified.

On a sunny day (Mon, 22 Jul 2013 10:52:41 -0700 (PDT)) it happened "M. Hamed" wrote in :

Thanks, nice table.