16 Apr
1999
16 Apr
'99
7:23 p.m.
On 16 Apr 99 at 23:21, Tony Duell wrote:
I've got a couple of old Eico tube amps that have both loudness and
level pots. Wasn't there also a problem related to changing amplitude.
These used pre-Crossley non-multiplexed external FM tuners so it was
related to any input not only signal detection. There's also a control for the
various phono recording types. e.g. Columbia, London, RIAA, Am78, and Eur78
Yeah, I got rid of a mid-quality Sony receiver with a click-click and all the
conveniences but with a digital tuner, because of that. Now I have to get up
Hi,
Could anyone tell me how a radio detects signals vs. static? There is a
little gauge on my radio that moves depending on the amount of noise vs.
As you know, a radio uses some kind of freqeuncy-selective filter to
selected the wanted station from all the others. And it then amplifies
that signal. But since all the different signals have different strengths
when they reach your radio (and a particular signal may even vary in
strength), you'd have to keep on adjusting the volume control as you were
tuning the set to ensure that (a) you didn't miss any signals and (b) you
didn't drive everyone mad when you hit the stronger signals.
So all modern radios (the idea was first used in the
1930's, I think)
have a circuit called an Automatic Gain Control (AGC) [Sometimes called
Automatic Volume Control - AVC - in older books). This circuit measures
the average level of the received signal and adjusts the gain (how much
the set amplifies the signal) so that all signals appear to have the same
volume. Weak signals get amplified more than strong ones.
Now, firstly static is always there, even when you're listening to a
strong station. Don't think it's stronger when there's no station - it's
not. But if there's no station, then the AGC circuit makes the set
amplify the (non-existent, really) signal as much as it can, so the (very
weak) static sounds quite loud
Secondly, by measuring the control signal that controls the gain you can
get some idea of how strong the signal is. The less gain the radio is
using, the stronger the signal. That's almost certainly what the meter on
your radio is measuring.
I have some older equipment that doesn't TMK use AGC that has signal level
meters and as well there were the tube signal level indicators. Is that method
only used on the cheaper newer sets ?
signal. I
would guess that the digitally tuned radios that skip over the
frequencies that are pure static work in the same way. What is this way?
Yes. Unless they detect a suitably strong signal, they'll skip over it. A
real pain if you're trying to receive a very weak signal.
-tony
from the couch if I want to change anything. Gives me
some exercise. :^))
ciao larry
lwalker(a)interlog.com
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