Finding out what frequency i am on

[Electro132]

Hi,

I am seeking to know how i could go about getting a variable inductor into my LC tank circuit, as well as what components i will be needing. I have a 6 - 30 pf trimcap for variable tuning within an lc tank circuit but found out that i could also get the coil to be fixed or variable and would like to know how could this be done. Furthermore, I would like to know whether my trimcap is useful in the khz range or will i need to get another one and if so, which one.

Also i would like to know how can i digitally view what frequency i am on so i can keep track of which frequency i have come across rather than just having the math done.

Any help is much appreciated, Cheers!

 

[Arouse1973]

Can you tell us more about your project and what it is. Do you have a circuit diagram? You can get variable inductors, they work by varying the position of the internal ferrite core. The capacitor value will depend on the inductor chosen and the LC ratio required. If you can give a bit more information I am sure we can help.
Adam

 

[Electro132]

Well, i have 2 projects:

one is about being able to digitally display the frequency being used in the LC tank circuit using LCD displays or even just using the digit numbers. With it i can distinguish where i am on the frequency chart and work my way around

and the other is to understand how LC circuits work along with antennas. I think they have 2 different LC tank circuits but not quite sure... <----- This is just for my own knowledge

 

[Arouse1973]

You have to be careful just making an oscillator with an antenna as you might contravene your local law regarding transmission of electromagnetic waves and the power it develops may interfere with other equipment. You need to check out what ISM bands you are allowed to use and be extremely careful you don't exceed the power allowed for transmission in that band.

When you say KHz range can you be more specific?

To be honest for now I would just stick to an oscillator without an antenna and have a play with that. When building the circuit you also have to be sure you have not created any accidental antennas from your PCB layout which could also radiate in wires connecting to the circuit.

Do you have an oscillator circuit in mind and are you planning on trying to measure a sine wave to workout the frequency or converting a sine wave into a square wave and then measuring the period of this waveform? If you are planning on measuring very high frequencies then you could square up the signal from the LC circuit and use a counter to reduce the frequency and do a conversion on that to find out what the frequency is.

Just some thoughts
Adam

 

[Electro132]

Hi, sorry for the long wait. I was on holiday. Anyways, first and foremost, i need to know how to calculate how many turns on a coil i need to achieve a certain frequency. For e.g. How many turns on a coil does it take to get 22, 000 khz? So far i've checked online and found that it didn't make any sense to me how to find out the frequency i want. I mean does the coil gaps between each other determine which frequency i am on? I know the width of the coil, the length and diameter plays a part but is there some sort of guide i can use to find out where i am?

Is there a guide like this (this is just an example):

1 coil turn = 10 khz
5 coil turn = 100 khz
10 coil turn = 1000 khz
15 coil turn = 10,000 khz

So i know how many turns i need exactly and where i am on the frequency chart?

 

[davenn]

google LC calculator

for kHz range, you will probably need a cap in the many 10's to several 100 pF

Buy a frequency counter

Dave