IF transformers , impedence

[salviador]

Hi,
I have a question about IF trasformer and impedence:

http://www.mouser.com/ds/2/449/XC-600131-205883.pdf

make an example, I take a "42IF103-RC" in the datasheet

Pri impedance : 20K
Sec impedance: 6K
Turns Pri: (1-2) 103 and (2-3) 50
Turns Sec: (4-7) 27


Ok, I want to test the formula of the impedance and number of turns:

sqrt(Zpri/Zsec) = Npri/Nsec

If I apply this formula:

sqrt(20000/6000) = (103+50)/27
sqrt(3.333) = 5.6

why not bring ??

[German_EE]

The impedance also depends on the core material and the frequency. Your IF coil will therefore be 20K/6K when used at 455 KHz.

[jimmc]

There is an error on the datasheet  the column marked 1-2 should read 1-3.
The schematic is correct, the primary is 103 turns (1-3) tapped at 50 turns (2-3).
The normal connection is input 2-3 giving a turns ratio of 50/27 = 1.85 :1 and an impedance ratio of 3.43:1 close enough to 20k:6K.
(Less than 100% coupling accounts for the difference.)

The 20k impedance is chosen to give the required bandwidth and loaded Q. (Unloaded Q =75, loaded Q = 30)

Jim