Re: coupling factor??.....

On Wed, 27 Apr 2005 14:14:28 UTC, xiibweb@xxxxxxxxxxx wrote:

> Hi,
>
> I would like to know why coupling factor for IF transformer affects the
> centre frequency. I hv a circuit in PSpice with two IF transformers...
> and when I reduce the coupling factor I get the required centre
> frequency which is 455KHz...
>

Have you checked the frequency response over a range of (say) +/- 25
kHz? You may find that the simulation is showing a double peaked
response. Coupled tuned circuits used to be described as undercoupled,
critically coupled and over coupled. When circuits are undercoupled,
the centre frequency is correct but the output amplitude is reduced.
With critical coupling the maximum output is obtained with a single
resonant frequency. If overcoupled, the circuit has two peak
responses, one below the nominal resonant frequency and the other
above. The output at the nominal resonant frequency is reduced
relative to the two peaks. Overcoupling can be useful in increasing
the bandwidth of a coupled circuit.

Refer to one of the old textbooks for more explanation - I've just
checked it in a book called "Radio Engineering Handbook" editied by K
Henney and published in 1950. Terman would cover it but I don't have a
copy.

--
Jim Backus OS/2 user since 1994
bona fide replies to j <dot> backus <the circle thingy> jita <dot>
demon <dot> co <dot> uk

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