Jump to content
Electronics-Lab.com Community

A chock coil


walid
 Share

Recommended Posts

In many FM Txs they use a coil connected from the o/p of a high frequency stage to the power supply, this coil is of fairly larg value (for example 100uH). The purose of using such coils is to chock (prevent) high frequency sigals from going to other stage through the power supply.
For example in 100 MHz FM Tx, they use 100 uH coil which has impedance of (2*pi*f*L) about 63 Kohm.
My question: Is it better to use 1 mH (1000uH) which has 630 Kohm ot taking the size into account?
Or is this true:"the more L the more chock effect"? What are the limits?
thanks.

Link to comment
Share on other sites

Oops! isn't that also too big, i belive that a cap that big at this freq lives a life of its own, and dont decouple the emitter resistor very well! Something else curious with this schematic? Of course, no emphasis! Maybee thats why the coupling cap between the mic and the input is so small! Moore?

//Staigen

Link to comment
Share on other sites

Hi Walid

How you think calculate this value, this what i need to know

Thumb of rule: Not moore than 1 nF at 100 Mhz for decoupling! This goes for toobz, but i think it is relevant for transistors too, it dont have to do with if it is a transistor or a tube.

gesign gesign gesign gesign gesign gesign gesign gesign gesign

What is "gesign"

To Audioguru: Hehe :D

//Staigen
Link to comment
Share on other sites

Until you are experienced in circuit "gesign" it is advised that you build a "bototype". (He, he.) ;D
Then you can tweak parts values in the prototype to make it work as well as it can.
In the prototype you will learn that 100MHz is a very high frequency.
At such a high frequency, you will learn that 100nH works well, but 100uH works like a capacitor.
At such a high frequency, you will learn that a 1nF ceramic cap with short leads works very well, but 100nF is an inductor. ;D

Link to comment
Share on other sites


Until you are experienced in circuit "gesign" it is advised that you build a "bototype". (He, he.) ;D
Then you can tweak parts values in the prototype to make it work as well as it can.
In the prototype you will learn that 100MHz is a very high frequency.
At such a high frequency, you will learn that 100nH works well, but 100uH works like a capacitor.
At such a high frequency, you will learn that a 1nF ceramic cap with short leads works very well, but 100nF is an inductor. ;D


I have not oscilloscope or other devices to monitor the change so i ask
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
  • Create New...