Hi,

I want to know at what frequencies the transmission line effects will be considered ?

 

First, you need to know how to use Google.

 

Welcome to AAC!
What signal? What transmission line? What effects?
In theory, a signal of any frequency passing along any line will be affected by the line's properties.

 

Adding to what Alec_t said, I usually don't worry much about transmission line effects in analog signals until the length of the conductor approaches 5% of the wavelength of the highest significant frequency component of the signal involved.

Whether to or the extent to which one needs to worry about transmission line effects really depends on what sort of problems and to what extent are tolerable in your system.

 

Adding to what Alec_t said, I usually don't worry much about transmission line effects in analog signals until the length of the conductor approaches 5% of the wavelength of the highest significant frequency component of the signal involved.

Approaching from which side?
If I'm working with a 300Mhz single frequency which has a wavelength of a meter then I don't have to worry about transmission line effects
if my traces are over 5cm or under 5 cm?

 

From zero.

A zero length trace or wire is not a transmission line, so any trace that looks very short to the highest frequency component of significant amplitude in the signal under consideration is less likely to exhibit significant transmission line effects than a longer trace or wire.