In this month's issue of QEX (the ARRL publication oriented toward radio technology) there is a comprehensive review of the causes and effects of noise in receivers -- a big concern if you are trying to "work DX", avoid adjacent channel overload, etc. The author castigates the designs of the last 20 years -- one of the points germane to <b>audio</b> is that significant noise in recent designs is attributable to the use of diode switching, as compared to relay switching, or plain 'ol turn the knob. The noise floor of the mechanically switched receivers is much better than modern (shall we say "so-called" modern) designs.
There are a whole number of other problems in these applications such as phase jitter in local oscillators (sound familiar?), inadequate suppression of oscillator harmonics etc, inexpensive filtering compared to "so-called" old fashioned crystal lattice filtering. Interesting article.
There are a whole number of other problems in these applications such as phase jitter in local oscillators (sound familiar?), inadequate suppression of oscillator harmonics etc, inexpensive filtering compared to "so-called" old fashioned crystal lattice filtering. Interesting article.