Why are more gangs better?

Just curious, why is a 4 gang tuner better than a 3 gang tuner? What advantage does this give to the listener/user?
Thanks!
 
danbennett2u said:
Just curious, why is a 4 gang tuner better than a 3 gang tuner? What advantage does this give to the listener/user?
Thanks!

Each gang of a variable capacitor is teamed up with an inductor to form a tuned circuit. One gang is for the local oscillator and the rest are for the input RF amplifier stages. The more tuned stages in the tuner front end the better and sharper the RF selectivity will become. This helps for preventing a very strong station nearby a desired station from spilling over and causing interference.

Normally the minimum gangs for a FM tuner is 3 (LO ocs, RF input, mixer input) and additional stages will support either more RF amplifier stages or just more antenna input stages. So the number of gangs indicates the complexity and performance capability of the front end of the tuner.

Now a days the gangs of variable capacitor have been replaced by solid state devices called varicaps. These are 2 lead diodes that change their capacitance by the amount of reverse voltage bias appied to them, a voltage controlled variable capacitor. They are much cheaper to produce then the mechanical variable capacitor but they don't perform as well as the 'Q' (selectivity) is not as good.

So while there are certainly additonal things that make a good tuner, including IF and demultiplexer circuitry complexity, the number of gangs can give a quick indication of the quality and cost of a tuner. Probably just as effective an indicator is if the tuner has selectable IF bandwidth controls. The best tuners come with two or more bandwidths to adapt the IF amplifiers to the signal being recieved. Wider gives better audio frequency and disportion specs but narrower gives better weak signal reception.

Lefty
 
Is the varicap the same thing as the varactor used by Fisher in thier early SS units? Never thoguht to ask the question until now.
 
Well, I always said the the old boy really had an interesting unit. He was years ahead of everyone else in the design and pioneered the preset concept used today. Maybe the TX series is the receiver design that is the most influential over the long run; as far as tuner design goes.
 
Thanks!
Let me make sure I have this straight:
1 - More gangs can give more selectivity.
2 - More gangs in itsself will not really influence the sensitivity, but may indicate that other parts of the tuner are higher end?
 
danbennett2u said:
Thanks!
Let me make sure I have this straight:
1 - More gangs can give more selectivity.

Yes, more front end selectivity, but does not determine selectivity of the IF stages where the number and type of IF filters determine the selectivity. RF selectivity helps with front end overload type problems and IF selectivity determines how well it handles adjacent channel interferance.

2 - More gangs in itsself will not really influence the sensitivity, but may indicate that other parts of the tuner are higher end?

Again yes, however more front end gangs may support 2 stages of RF amplifiers which would have better sensitivity specs, it depends on the specific model.

All in all one can make the case that them more gangs the better but there are many of factors that determine the overall qualities of a tuner. The single most important factor IMHO is one's antenna selection. Even a TOTL tuner if supplied with a weak signal cannot perform as well as a lesser tuner that is hooked up to a better antenna.

Lefty
 
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