hello!

radio_rookie wrote:

... IF was used in Superhet transceivers.

well, IF __is__ used in superhet receivers...

My question is why
doesn't anyone use zero IF now a days. ....

In fact, you can very well use zero IF in a receiver: what you get,
doing so, is a "direct conversion", or "synchrodyne", receiver, which
is simple, easy to design and realize, cheap, and yet can offer very
high level performances - as is well known to radio amateurs

But... yes, there's a but, and a price to pay: in a DCR, you put all the
required gain (a hundred of dBs, give or take a few) in the base band
(or audio frequency) chain, and this is bad for noise! Most electronic
devices are sensitive to pressure, and a sound is a pressure wave... you
may end up with something which can be quite a decent microphone!

Moreover, in a DCR it may be rather difficult to implement an effective
AGC, so switching from weak to loud signals may be annoying, and even
dangerous for hearing! Also, it's not easy to obtain a reasonable S-meter...

Last, but not least, a simple DCR is inherently a DSB receiver, lest you
implement it with rather complex mixers - which add much to the circuit
total complexity.

Adding all of this up, a superhet may be a good choice...
--
73 es 51 de i3hev, op. mario

Il vero Radioamatore si riconosce... dal call in firma!
- Campagna 2005 "Sono un Radioamatore e me ne vanto"

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