Balanced VLF Tx

[Aziz]

BTW,

regarding the transistors in the oscillator:
Low power, high beta (current gain), mid voltage range (40-60 V) should do a good job.
Remember, the transistors are just injecting a small amount of current into the resonant tank. No need for high current rated transistors (they have generally low beta). Better to use a high beta transistors (C type), that the oscillation can start with just low base currents.

I think, I can claim to have "invented" the most efficient oscillator in the wourld. *LOL*
Ok, this was a joke. I'm sure, someone has invented it already.

I love capacitors, inductors and chokes (inherently).
Cheers,
Aziz

[Davor]

But I hate to see a typical electronic components shop completely void of any useful cores

[Aziz]

But I hate to see a typical electronic components shop completely void of any useful cores

Hey, here is the poor man's solution:
Make a lot of iron powder by grinding some peace of soft iron (using a file).
Make a negative toroid type former (wood, plastic or something else). Take a two component glue and mix it well with iron powder. Fill the mixture into the toroid former. Let dry it. Get the core out of the former and grind it a bit. That's it. Measure the inductance and Al-value and wind the appropriate inductor.
Aziz

[WM6]

Hey, here is the poor man's solution:
Make a lot of iron powder by grinding some peace of soft iron (using a file).
Make a toroid type former (wood, plastic or something else). Take a two component gule and mix it well with iron powder. Fill the mixture into the toroid former. Let dry it. Get the core out of the former and grind it a bit. That's it. Measure the inductance and Al-value and wind the appropriate inductor.
Aziz

What sort of iron? Pure? Oxide?

Assume that this will be applied to choke?

[Aziz]

What sort of iron? Pure? Oxide?

Assume that this will be applied to choke?

Yes, pure iron. A high susceptible iron with less remanent magnetism. Usually a soft iron (steel isn't convenient as it has some remanence).
You can also use magnetite or maghemite powder.
The concentration of the susceptible material must be experimented. Avoid the conductance of iron powder particles (less iron powder, more epoxy glue).

Maybe it is better to look for electronic waste and recyle the toroid cores. You can save a lot of messy work in this case. The inductor value in the choke isn't much critical. It will work for a wide range of inductivities too. The ripple noise on the Vcc and Vee will get either more or less.

Aziz

[WM6]

The inductor value in the choke isn't much critical. It will work for a wide range of inductivities too. The ripple noise on the Vcc and Vee will get either more or less.

Aziz

Can we say approximately which inductance to follow on wound choke? Or in which range it have to be?

Assume that all toroids out of broken switch power supply (as PC power supply) would be ok.

[Davor]

There are mainly two parameters, Al-value and saturation, and for both you are in complete dark when making such cores. Considering you do not expect any significant current here, you are not going to saturate such cores regardless how hard you try, it is just the Al-value you are after.

I think this approach is messy, but in cases of emergency...

BTW, you can obtain pure and very fine iron oxide dust packed by kilos in pottery hobby shops. It is used for colouring of the pottery Price is about 15Eur/kg.

[ODM]

I'd go scavenging for a complete toroid choke or just the core from some power supply or rundown equipment, instead of messing around with epoxy and filing iron. But then again, I don't etch my own transistors either

For current such as 50-100mA a generic power supply series choke for 1A or more can support extra turns for raised inductance, and more isolation from the supply at the osc frequency - As long as the inductor is not saturating with the oscillator's DC current. It's probably better to look for inductors used for filtering, not as the switching inductor, to make a "lossy" choke. Tracing parasitic oscillations to the emitter is nasty!

If I was scavenging a part for this purpose and wouldn't do a simulation, I'd probably keep adding turns while measuring the current and voltage across the inductor, and that needs a 'scope... Anyone building MDs or other electronics should really have one.

[Davor]

Tell me about it

However, I don't think DC is going to be a problem because it is in a neighbourhood of 15mA. Iron cores might be a better choice because of better Al and saturation at lower frequencies. Ferrites rock at 100kHz and more.

I think there is a less messy way of keeping a DIY core together: white glue. Epoxy has a nasty habit not to cure if too much metal dust is added to it, and I really have no intention finding out the right amounts of hardener etc.

[Aziz]

Hi all,

the inductor (choke) isn't critical at all. There is a small portion DC current and a small portion AC current flowing through it and we are by far far from saturating the toroid core. Don't confuse with the coil current and the injecting current into the LC tank. The injecting current is very low and it compensates the losses in the transmitter oscillator.


Even the higher ripple noise with less inductivity chokes (220 µH .. 470 µH) isn't critical too. The ripple noise on the Vcc/Vee line is synchronized with the oscillator. The amplifier fed through ripple noise on Vcc/Vee is synchronized with the oscillator too. No problem.

Inductor values of 1 mH .. 2 mH and around it should be enough.

Aziz

[Aziz]

Patents!!!! The ******* patents!!!!

Last edited by Qiaozhi; 10-16-2012 at 04:14 PM. Reason: Removed swearing from post - Warning #2 !! Are you trying to take a sabbatical from Geotech?

Aziz

How about cancelling my warnings #1 and #2 Mr. Q?
Warning #3 would very likely ban me and the people here will perhaps miss my freaky & mad contribution. Even PJ and his brothers would get sad.
Aziz

[Sergey_P]

Aziz, no current generator in your schema. It is necessary for the parallel tank circuit

[Aziz]

Aziz, no current generator in your schema. It is necessary for the parallel tank circuit

Yep, the current source and sink solution isn't showed yet. But one can easily plug at the emitters of the transistor pairs and V+/V- node. This is a very trivial job.

I want to make the very simplified solution, where the TX coil current gets modulated by the targets/ground. If this isn't working properly, then the current source/sink method will be tested.
Aziz

[Sergey_P]

<very simplified solution> - the field-effect transistor (FET)

[Aziz]

<very simplified solution> - the field-effect transistor (FET)

Do you have actually a proposal? Comeon, share it with us.

Aziz