"isw" wrote in message
...

snip


After you get done talking about modulation and sidebands, somebody
might want to take a stab at explaining why, if you tune a receiver to
the second harmonic (or any other harmonic) of a modulated carrier (AM
or FM; makes no difference), the audio comes out sounding exactly as it
does if you tune to the fundamental? That is, while the second harmonic
of the carrier is twice the frequency of the fundamental, the sidebands
of the second harmonic are *not* located at twice the frequencies of the
sidebands of the fundamental, but rather precisely as far from the
second harmonic of the carrier as they are from the fundamental.

Isaac

Whoa. I thought you were smoking something but
my curiosity is piqued.
I tried shortwave stations and heard no harmonics.
But that could be blamed on propagation.
There is an AM station here at 1.21 MHz that is s9+20dB.
Tuned to 2.42 MHz. Nothing. Generally the lowest
harmonics should be strongest. Then I remembered
that many types of non-linearity favor odd harmonics.
Tuned to 3.63 MHz. Holy harmonics, batman.
There it was and the modulation was not multiplied!
Voices sounded normal pitch. When music was
played the pitch was the same on the original and
the harmonic.

One clue is that the effect comes and goes rather
abruptly. It seems to switch in and out rather
than fade in an out. Maybe the coming and going
is from switching the audio material source?

This is strange. If a signal is multiplied then the sidebands
should be multiplied too.
Maybe the carrier generator is generating a
harmonic and the harmonic is also being modulated
with the normal audio in the modulator.
But then that signal would have to make it through
the power amp and the antenna. Possible, but
why would it come and go?
Strange.

--
rb

In article ,
"Ron Baker, Pluralitas!" wrote:

"isw" wrote in message
...

snip


After you get done talking about modulation and sidebands, somebody
might want to take a stab at explaining why, if you tune a receiver to
the second harmonic (or any other harmonic) of a modulated carrier (AM
or FM; makes no difference), the audio comes out sounding exactly as it
does if you tune to the fundamental? That is, while the second harmonic
of the carrier is twice the frequency of the fundamental, the sidebands
of the second harmonic are *not* located at twice the frequencies of the
sidebands of the fundamental, but rather precisely as far from the
second harmonic of the carrier as they are from the fundamental.

Isaac

Whoa. I thought you were smoking something but
my curiosity is piqued.
I tried shortwave stations and heard no harmonics.
But that could be blamed on propagation.
There is an AM station here at 1.21 MHz that is s9+20dB.
Tuned to 2.42 MHz. Nothing. Generally the lowest
harmonics should be strongest. Then I remembered
that many types of non-linearity favor odd harmonics.
Tuned to 3.63 MHz. Holy harmonics, batman.
There it was and the modulation was not multiplied!
Voices sounded normal pitch. When music was
played the pitch was the same on the original and
the harmonic.

One clue is that the effect comes and goes rather
abruptly. It seems to switch in and out rather
than fade in an out. Maybe the coming and going
is from switching the audio material source?

This is strange. If a signal is multiplied then the sidebands
should be multiplied too.
Maybe the carrier generator is generating a
harmonic and the harmonic is also being modulated
with the normal audio in the modulator.
But then that signal would have to make it through
the power amp and the antenna. Possible, but
why would it come and go?
Strange.

Hint: Modulation is a "rate effect".

Isaac

Ron Baker, Pluralitas! wrote:
"isw" wrote:

After you get done talking about modulation and sidebands, somebody
might want to take a stab at explaining why, if you tune a receiver to
the second harmonic (or any other harmonic) of a modulated carrier (AM
or FM; makes no difference), the audio comes out sounding exactly as it
does if you tune to the fundamental? That is, while the second harmonic
of the carrier is twice the frequency of the fundamental, the sidebands
of the second harmonic are *not* located at twice the frequencies of the
sidebands of the fundamental, but rather precisely as far from the
second harmonic of the carrier as they are from the fundamental.

Isaac

Whoa. I thought you were smoking something but
my curiosity is piqued.
I tried shortwave stations and heard no harmonics.
But that could be blamed on propagation.
There is an AM station here at 1.21 MHz that is s9+20dB.
Tuned to 2.42 MHz. Nothing. Generally the lowest
harmonics should be strongest. Then I remembered
that many types of non-linearity favor odd harmonics.
Tuned to 3.63 MHz. Holy harmonics, batman.
There it was and the modulation was not multiplied!
Voices sounded normal pitch. When music was
played the pitch was the same on the original and
the harmonic.

One clue is that the effect comes and goes rather
abruptly. It seems to switch in and out rather
than fade in an out. Maybe the coming and going
is from switching the audio material source?

This is strange. If a signal is multiplied then the sidebands
should be multiplied too.
Maybe the carrier generator is generating a
harmonic and the harmonic is also being modulated
with the normal audio in the modulator.
But then that signal would have to make it through
the power amp and the antenna. Possible, but
why would it come and go?
Strange.

I've once listened to the first five harmonics of a
powerful medium wave transmitter (400 kW) at
a distance of some 300 m.
All harmonics gave normal audio; no strange
switching effects (Sony ICF-7600D).

What I'd like to know is if in such an 'experiment'
it can be excluded that (some of) these signals are
generated by the receiver itself.

gr, Hein

Hein ten Horn wrote:

I've once listened to the first five harmonics of a
powerful medium wave transmitter (400 kW) at
a distance of some 300 m.
All harmonics gave normal audio; no strange
switching effects (Sony ICF-7600D).

What I'd like to know is if in such an 'experiment'
it can be excluded that (some of) these signals are
generated by the receiver itself.


That much power that close to the receiver? Its a wonder you didn't
destroy the receiver's frontend.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

In article ,
"Michael A. Terrell" wrote:

Hein ten Horn wrote:

I've once listened to the first five harmonics of a
powerful medium wave transmitter (400 kW) at
a distance of some 300 m.
All harmonics gave normal audio; no strange
switching effects (Sony ICF-7600D).

What I'd like to know is if in such an 'experiment'
it can be excluded that (some of) these signals are
generated by the receiver itself.


That much power that close to the receiver? Its a wonder you didn't
destroy the receiver's frontend.

That particular receiver doesn't have much of a "front end"; diodes
(with protection) and straight into the first mixer. No RF stage, tuned
or otherwise.

Isaac

isw wrote:

That particular receiver doesn't have much of a "front end"; diodes
(with protection) and straight into the first mixer. No RF stage, tuned
or otherwise.


It can exceed the PIV of the protection diodes and cause them to
short, or explode. That crappy Sony design is where the harmonics came
from. The diodes, (or any other semiconductor) with enough RF can
generate a lot of spurious signals. It can even come from a rusty joint
in the area.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Michael A. Terrell wrote:
isw wrote:

That particular receiver doesn't have much of a "front end"; diodes
(with protection) and straight into the first mixer. No RF stage, tuned
or otherwise.

It can exceed the PIV of the protection diodes and cause them to
short, or explode. That crappy Sony design is where the harmonics came
from. The diodes, (or any other semiconductor) with enough RF can
generate a lot of spurious signals. It can even come from a rusty joint
in the area.

Is the ICF-SW7600GR significantly better performing
than the ICF-7600D on this?

gr, Hein

Hein ten Horn wrote:

Michael A. Terrell wrote:
isw wrote:

That particular receiver doesn't have much of a "front end"; diodes
(with protection) and straight into the first mixer. No RF stage, tuned
or otherwise.

It can exceed the PIV of the protection diodes and cause them to
short, or explode. That crappy Sony design is where the harmonics came
from. The diodes, (or any other semiconductor) with enough RF can
generate a lot of spurious signals. It can even come from a rusty joint
in the area.

Is the ICF-SW7600GR significantly better performing
than the ICF-7600D on this?

gr, Hein

I haven't seen the schematics of either model, but most portable SW
recievers suffer from no filtering on the front end, so are susceptible
to overload. A properly designed front end is expensive. Most
manufacturers would rather spend the money on eye candy to make it
attractive to those who don't know what they really need. This is
crossposted to: news:rec.radio.shortwave where the relative merits of
different SW radios are discussed.

I tend to use older, rack mounted equipment that I've restored and
when I have the time, I like to design my own equipment. I only have
one portable receiver, the RS DX-375, which is kept in my hurricane
emergency kit. It was bought on price, alone when it was discontinued
for $50, about eight or nine years ago. The power line and ignition
noise is so high around here that a portable is almost useless. After
the last hurricane, the nearest electricity was over 5 miles away for
about two weeks, and I was picking up stations from all over the world.
It reminded me of visits to my grandparent's farm back in the early
'60s, when their farm was the last one on their road with electricity.
They had nothing that generated noise, other that a few light switches,
when they were flipped on or off. I didn't have a shortwave radio, but
I could pick up AM DX from all over the country, late at night.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida