Hartley oscillators (inductances)

[watari]

Hi, I'm back again. I've been searching for more Hartley oscillator circuits in order to compare them with mine and check if it is right, also I took into account (and also I appreciate) your advices. gyulasun


First of all I would like to say that beta=200  was chosen looking at the  N3904 datasheet, given a 40mA current collector. Which, if i'm not wrong, 200 is its typical value.

I understand what you say about how i have to get a ratio L2/L1 close to beta,  and how a proper value of this beta has to be big enough to compensate loses. But in my search on the net, I found a website where they show you how to build a Hartley oscillator. The values of the inductances are; L1=1.2uH and L2=6.8uH and the ratio L2/L1= 5.67, what is bigger than 1 but clearly far away from every minimum value of beta given in  N3904 datasheet (that is what it uses), even in graphics. I did not calculated any other parameter yet, but, for what i know (that is not so much) either this does not fit well enough or what i know is simply not right.

If anyone of you wants, I can give you the link to that website in order to check it out by yourself.

Once more, thank you all.

[gyulasun]

In fact I did not really imply the Beta and the L2/L1 ratio should be connected and be 200, I implied the gain of the amplifier stage i.e. the collector and emitter impedance ratio which is to be related to the coils ratio (in my Reply #1 above).
Please forget considering the Beta,  when you choose the transistor type (2N3904), you already decided on Beta, right?

Do you really need to run the transistor at 40mA collector current? For LC oscillators in general the current is normally less than say 10-15mA, otherwise frequency stability suffers a lot. I would prefer any current between 5-10mA or so.

Gyula

[watari]

Hey guys!! I'm sorry for being absent for so long. I'm very busy these days and i have no time neither for playing with circuits nor for this forum (sigh). I don't know when i'll be able to pay attention to them. Anyway, as soon as i can i'll be back to work on this and i'll keep posting my results (and question).

regards

[watari]

Hi again!

I've been traveling for almost four month and I've been completely absent for that. I've had time enough to think over this project i want to do. And I came out with the conclusion that having an oscilloscope will help me a lot. But I don't know so much about them and I don't have any so I started a post right here in this forum  asking for advise to buy one. Until I dont get the oscilloscope I won't keep going omn with my porject.

I would like to invite you to this new post I started to give advise.

http://www.overunity.com/13842/best-oscilloscope-choice/msg372082/#msg372082

Once more, thanks!!