Vacuum tube equipment

Garrett Wollman
Thu Sep 1 12:54:48 EDT 2005

<<On Thu, 1 Sep 2005 12:37:39 -0400, John Francini <> said:

> They sell a number of high-quality radios, especially units with very 
> sensitive front ends (the part that actually detects, decodes, and 
> isolates the signal you want from all the others.)

For FM reception, sensitivity is rarely a problem any more.  Even the
fifteen-cent tuner-on-a-chip variety are sensitive enough to pull out
signals a few dB above the thermal noise floor.  The problem is
invariably one of selectivity: if your front end is too broadband, the
AGC circuit will be overloaded by strong nearby (in frequency and
location) signals and thus "miss" the weak signal you're trying to
tune.  The other common problem for cheap receivers is that they tend
to generate lots of intermodulation products internally -- enough that
the intermod can "capture" the detector even when there is otherwise
enough signal from the desired station to decode it.


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