Quote:
Originally Posted by RichardGM
I'm still a bit puzzled. Yes you need to filter out the image frequency and any nearby strong signals, but most domestic FM tuners do OK without multiple stages of filtering before the mixer. Excluding the BBC's very special case of a receiver "based at the site of a working VHF/FM transmitter", when/why are those extra stages of filtering needed? Is it to receive very weak distant broadcast transmissions?
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If we consider only the British market, then before the VHF/FM band got the commercial stations added in the seventies, there wasn't much interest in long distance reception because there wasn't much any different to what you were already in the service area of.
But designers of FM radios and especially hifi tuners had to develop models which could compete on a global market, and that meant countries where a much larger variety of broadcasts were available. S some listeners might want to listen to a station serving a town many miles away and not just the big signals of the broadcasters in their local town. So much more emphasis was on dynamc range in Germany and the US.
As Japan came to dominate hifi, they had little interest in models only suited to the British market.
So across the period of time where tuners were becoming more complex, several other changes were happening. The FM band was filling up with stations and progressively taking listeners away from AM. Globalisation of markets meant tuners had to have superset specifications to suit many countries so the same model could be flogged around the world, with just a switch for 50/75us de-emphasis.
So Britain started receiving receivers with more RF selectivity stages than it really needed, then it filled-up it's FM band and started needing them.
On the world stage, quintessentially British tuners like Quad FM3 and FM4 have some performance figures which are quite attractive, they are not very competitive in terms of managing to get reception of weak signals with strong local ones nearby, and the monster tuners with many tuned RF tanks start to win.
So by looking at a circuit diagram, you can see how far afield a company's marketing department was looking. And each is also a snapshot of the time it was planned.
David