Figure 1 - if amplifier filter block diagram
LAST MODIFIED:
IF amplifier transformers are simply tunable inductors, usually with an integral fixed capacitor, and are typically used inside cheaper transistor radios.
Mostly they are used as "synchronously tuned filters" because each stage is coupled by an active device.
Figure 1 - if amplifier filter block diagram
Now in the if amplifier filter block diagram schematic above here I've depicted three I.F. transformers separated by two stages of amplification which could be valves, transistors or integrated circuits. We will not consider the actual active or amplifier stages here, just the I.F. transformers. Another tutorial dealt with the details the IF amplifier filtering block itself.
Here we will confine ourselves to the I.F. transformers (or IF transformers) themselves. The information I have provided here may be regarded as merely being "typical" of what you might encounter inside a transistor radio. That means don't take it for granted that this "IS" the case. O.K.?
The data presented below deals with the Mouser transformers only. There are numerous other manufacturers including Toko and many others. The variety of similar looking, but indeed quite different, IF transformers is astonishing. The table covers 455 Khz IF transformers, 10.7 Mhz IF transformers and standard AM Radio band oscillator coils which are tuned by the 60 pF section of a 60 / 160 pF "plastic" variable capacitor.
If you ever see a complete Coilcraft or a J.W. Miller catalogue it is truly bewildering.
Figure 2 - if amplifier transformer schematics
Of course if your even only half awake you would realise the only difference between type 1 and type 2 is that the latter doesn't have the integral capacitor built in. Now look at this table. Just look at the variances in the "yellow" types alone.
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A typical Mouser spec sheet can be had here. Spec Sheet for a 42IF124
We will consider the first one from our table above 42IF101. Here I've left the 180 pF capacitor out of the IF amplifier transformer schematic simply for clarity, it is normally connected internally across pins 1 and 3.
Figure 3 - 1st IF amplifier transformer schematic
A typical practical application can be seen in the tutorial on AM Radio receivers.
if amplifier filters
AM Radio receivers
band pass filters
high pass filters
low pass filters
active band pass filters
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Updated 20th October, 2001