Well, first let me finish cussin' an E-mail program that has no easy way to
insert a snippet from another E-mail. Then let me see if I can find a way to
explain something in absolutely non-technical terms so everyone can follow
along.
>> Steve Ellington, N4LQ, asks for either an explanation, expansion, or
explicaton of my previous post.
First, we classify and identify sounds by frequency, by intensity, and by
relative phase. Where the frequency and the intensity are similar, as they
are in much Amateur work, our ears do a wonderful job of separating similar
sounds by phase difference.
The simplest detectors, from the galena crystal on, had little or no effect
on relative phase between incoming signals. Neither did the simple tube
circuits from Armstrong to at least the first up-converting solid state
recievers. (No, I'm not knocking up conversion. That's a time reference!)
So most of the time it was pretty easy to separate the news on the Red
network from that on the Blue network, today's NBC and ABC, even when they
were coming in at approximately the same signal strength.
So there was usually no confusion between the Red's report on General
McAuliffe's defense of Bastogne and the Blue's reports of McArthur's progress
in the Pacific. Even though the names were similar enough to be confused.
And at least some, my father was one, could follow as many as four separate
radio "channels" at the same time when propagation was such that four
stations came in with about the same signal strength.
However, there were times when selective fading and multipath caused phase
shifts on the signal path(s) and upset the relationship between R and B. The
signals were no longer sharp and distinct, they were "smeared." During those
periods it was difficult to separate two voices. They were, in a manner of
speaking, "in phase," and were from somewhat to completely unintelligible.
Now, under most circumstances the simplest diode detector can provide audio
that the ear can separate into all its individual components. While product
detectors CAN be designed that preserve the phase relationships between
descrete signals, very few are. And while the JRC has many shortcomings, it
has a very good detector.
But very few "modern" rigs can provide an output that my ear can separate
into separate and intelligible channels of information. Most modern rigs
"smear" the incoming signals, either in their IF strips, their filters, or
their detectors, so multiple signals wind up like the signals on a bad AM
path, "in phase." My ears at least are no longer able to easily separate and
recognize such distorted signals.
Considering the number of times I have heard DX and contest stations come
back to a calling station and get no response I suspect many suffer from the
same problem I have.
The solution? Take as much care in designing low distortion IF strips,
bandpass filters, and detectors as you would in designing a general purpose
public address "medium fidelity" audio system.
After all, the IF and detector in the family's battery powered Watterson was
only designed to provide "telephone quality" fidelity. But even with its
cracked speaker cone it was far more intelligible than many of today's wonder
rigs.
73 Pete Allen AC5E
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