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Sci.Electronics.Basics -> AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
There are 269 messages in this thread.
You are currently looking at messages 260 to 269.
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Author: Hein ten HornDate: 17:46 17-07-07
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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
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Author: Hein ten HornDate: 17:46 17-07-07
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isw wrote:
> "Ron Baker, Pluralitas!" wrote:
>>
>> Then you understand Fourier transforms and convolution.
>
> I suppose so; I've spent over fifteen years poking around in the
> entrails of MPEG...
Ever learned, unfortunately seldom used.
What can radio hobbyists do with Fourier transforms
nowadays? (Nowadays, for aids and appliances like
software and spectrum analysers take over some work.)
If somebody could provide some examples I'd be grateful.
Thanks.
gr, Hein
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Author: Michael A. TerrellDate: 00:53 18-07-07
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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
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Author: iswDate: 13:59 18-07-07
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In article <469D9CB6.1A35A5C5@earthlink.net>,
"Michael A. Terrell" <mike.terrell@earthlink.net> 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
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Author: Michael A. TerrellDate: 14:44 18-07-07
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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
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Author: Hein ten HornDate: 16:42 18-07-07
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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
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Author: Michael A. TerrellDate: 21:40 18-07-07
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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
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Author: msgDate: 22:12 18-07-07
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Michael A. Terrell wrote:
> I only have > one portable receiver, the RS DX-375, which is kept in
> my hurricane emergency kit. It was bought on price, alone...
I had one and was quite disappointed by its image response (even in
the absence of strong signal IMD, overloading, etc.). For example,
WWV on 10 Mhz was equally strong on 9545 kHz. I never saw the
schematic so I know nothing about its front end and evidently
it is single conversion but one would have hoped for a varactor
tuned preselector ;)
How is image rejection on yours?
Cross-posts limited to sci.electronics.basics and rec.radio.shortwave
Regards,
Michael
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Author: Michael A. TerrellDate: 00:49 19-07-07
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msg wrote:
>
> Michael A. Terrell wrote:
>
> > I only have > one portable receiver, the RS DX-375, which is kept in
> > my hurricane emergency kit. It was bought on price, alone...
>
> I had one and was quite disappointed by its image response (even in
> the absence of strong signal IMD, overloading, etc.). For example,
> WWV on 10 Mhz was equally strong on 9545 kHz. I never saw the
> schematic so I know nothing about its front end and evidently
> it is single conversion but one would have hoped for a varactor
> tuned preselector ;)
>
> How is image rejection on yours?
Its acceptable for emergency, but not what I'd want for daily use.
I have a 50 KW FM transmitter and multiple cell sites within a mile
Right now I'm restoring a 1950's era national NC183R with a properly
designed front end, with two tuned RF preamp stages.
http://bama.edebris.com/download/national/nc183/nc183.pdf See page 16
for the front end circuitry. (855 KB (876,468 bytes))
I also have a HP 312B frequency selective voltmeter:
http://bama.edebris.com/download/hp/312bd/hp312bd.pdf (106 MB download).
--
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
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