Hello friends,

Figure 2..
As gain is a function of frequency in an rf circuit and to make gain constant between two tuned circuits for whole passband and to achieve this special techniques are being employed and one of them is involving mutual inductance to manipulate the gain in predetermined way. The equivalent mutual inductance m is the sum total of various planned and unplanned coupling prevalent in the primary circuit.

The eq. mutual inductance m, seeks to maintains its value constant around every frequency of the vhf broadcast band. This is possible because m has two component one is fixed and other is variable with frequency. This variable component is higher at high frequency. This variable second component is subtracted from the fixed one so m is less at high frequencies and at lower frequencies vice versa making m a little high. So in both of these cases m has been observed to put its value apparently constant thus maintaing gain constant over the frequency range in demand.

The coupling circuit used to achieved constant gain is shown below..
In the figure 9.16B Xm should be independent of frequencies to bring gain constant .....
How exactly this is achieved..?
How this compensation works..?

Figure 1.



Figure 2.

 

It may be instructive to try an LtSpice simulation, just picking some arbitrary component values according to the suggestions stated. There are one or two command instructions in the LtSpice program which allow the generation of both magnitude and phase over a range of frequencies. ... Have never used the mutual inductance parameter, so this is more or less a guess.

 

Have never used the mutual inductance parameter, so this is more or less a guess.

Yes I think that mutual inductance M is acting as an equalizer which have parameters which adjust or lower itself at high frequencies maintaining gain constant...But according to text there is a difference between Eq. mutual inductance m and Mutual Inductance M..however I am not sure about this equalizing action of the circuit.....needs more clarification..

 

For gain to be constant, constant coupling is required which is established by either a fixed mutual inductance M or a constant coupling coefficient k. Now according to formulas... Xm=wM+1/wCm and Xm=1/wCL+Ch/wC1C2..and if I do the substitute the values then for each frequency Xm will vary which in turn change the value of M which then alter the value of k will also changes the coupling so gain changes.
so what makes gain not to vary...