Please correct me-o/p impedance?

[samy555]

This circuit of the site:
http://www.talkingelectronics.com/projects/27MHz Transmitters/27MHzLinks-1.html

I assume that antenna impedance = 50 ohm
If I ignore the 8-turns ferrite coil, then tried to calculate the antenna impedance that seen looking into point A:
C1 =100pF, C2=150pF and for the inductor L1, I'm supposed 0.5 mm wire diameter according to images, and radius = 5 mm, length = 1 cm, and therefore has inductance approximately = 450 Nano Henry.

The 50 ohm antenna appeared to be only 73.7 ohm!!!
Now we turn to the 4:1 turns ratio transformer:

Zs: the total impedance connected to the secondary windings of the transformer
ZP: the total impedance connected to the primary windings of the transformer

My question is: Do I after all these calculations, I can say that the output impedance of the oscillator = 1.8 Kohm?

I thank you for the patience to read all of my long question

 

[nilses]

Hello,

Go to google and search for: antenna impedance calculator, you will get many hits with examples.
Som radio amateurs may also help, or the ARRL Handbook (for Ham radio operators).

The simple circuit shown has the filtering on the output to match a short antenna and stop harmonics causing interference with other services.

The circuit is used in almost all remote controlled toys and el cheapo walki-talkies.

Good luck with the maths !

regards,

Nils

 

[samy555]

Thank you for your fast response
I do not ask about the antenna impedance
I just want to conclude the value of the output impedance of the oscillator???

 

[godfreyl]

Hi
What you calculated is the load impedance driven by the oscillator, not the output impedance of the oscillator.

 

[samy555]

Hi
In order to match between the antenna and the oscillator output impedance, we must know the value of each
If = 50 ohm antenna almost
What is the value of the output impedance of the oscillator?
If you do not have the time to help me, it is possible to give me some websites that talk about this topic
Thank you
Thank you