AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
 

Don Bowey wrote:

AM is a process of frequency multiplication. Now you tell me where you
think such multiplication takes place on a phone line, and I'll follow-uo by
telling why you're full of crap.

SIMECS!


It is all right before your eyes, if you can't see it by now, forget it
.... perhaps at a later date. I know your frustration, I have seen the
mentally handicapped attempt to deal with the real world and it end only
in frustration ... perhaps a change of meds is in order ...

JS

AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
 

On 7/1/07 2:57 PM, in article , "John Smith I"
wrote:

Don Bowey wrote:

AM is a process of frequency multiplication. Now you tell me where you
think such multiplication takes place on a phone line, and I'll follow-uo by
telling why you're full of crap.

SIMECS!


It is all right before your eyes, if you can't see it by now, forget it
... perhaps at a later date. I know your frustration, I have seen the
mentally handicapped attempt to deal with the real world and it end only
in frustration ... perhaps a change of meds is in order ...

JS

I see..... You finally admit you don't understand AM at all and can't
justify your statement. It's what I expected.

Now, run off and play in the street with your tinker toys.

"Radium" a COMPLETE IDIOT... - More Likely An In-Complete-Want-To-Be [.]
 

On Jul 1, 2:28 pm, Don Bowey wrote:
On 7/1/07 2:11 PM, in article
om, "RHF"





wrote:
On Jul 1, 12:50 pm, "Porgy Tirebiter" wrote:
"Radium" wrote in message

groups.com...

On Jul 1, 7:24 am, wrote:
Analog cells phones should stop using FM and should start using AM
between frequencies of 40,000 to 285,000 Hz.

I chose 285 KHz to be the highest radio frequency for cell-phones
because it is roughly the highest-frequency categorized as "long wave"
radio.

- IDIOT!......complete idiot......

PT - Once again why waste your time replying
to his posts ? ? ? {Oops Like I Am Doing Too !}

Actually "Radium" would appear to be an
In-Complete-Want-To-Be driven by the 'urge'
to Post these Forever Ponding Questions
for others to charge at like Don Quijote's
quest to slay Windmills {a fool's errand}
http://en.wikipedia.org/wiki/Don_Quixote
http://en.wikipedia.org/wiki/Fool%27s_errand

FWIW - While many of his Post might fit into
the "sci.electronics.basics" NewsGroup; often
they would be consider OFF-TOPIC in other
NewsGroups like : rec.radio.shortwave,
rec.radio.amateur.antenna, alt.cellular.cingular,
alt.internet.wireless, etc

IMHO - In another life "Radium" would have
made a great High School Science Teacher :
Who's Students when on to do great things
with their lives :
Because "Radium" Touched Them With A Thirst
For Knowledge And A Quest For Answers.


- But a teacher MUST be rational.
- You rate Radium with more potential than I can.
- This most recent post is really off the wall.

"Radium" -and- 'Rational' now there is an Oxymoron !
http://en.wikipedia.org/wiki/Oxymoron






-but- These NewsGroups are NOT a High School
Science Class -and- "Radium" is just being 'radium'.
http://en.wikipedia.org/wiki/Radium

-alas- Our "Radium's" Half-Life of Readable Interest
http://en.wikipedia.org/wiki/Half-life
is at best about 16.04 Seconds ~ RHF
.
.
. .- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

DB remember that I did write :
Actually "Radium" would appear to be an
In-Complete-Want-To-Be driven by the 'urge'
to Post these Forever Ponding Questions
for others to charge at like Don Quijote's
quest to slay Windmills {a fool's errand}
http://en.wikipedia.org/wiki/Don_Quixote
http://en.wikipedia.org/wiki/Fool%27s_errand

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
 

Ian Jackson wrote:
In message , cledus
writes
Radium wrote:
Hi:
Please don't be annoyed/offended by my question as I decreased the
modulation frequency to where it would actually be realistic.
I have a very weird question about electromagnetic radiation,
carriers, and modulators.





No offense but please respond with reasonable answers & keep out the
jokes, off-topic nonsense, taunts, insults, and trivializations. I am
really interested in this.
Thanks,
Radium



The fundamental answer is no, it is not possible to generate AM where
the baseband signal is a pure 20 kHz sinewave and Fc20kHz. The
reason is that the modulated waveform consists of the sum of a
sinewave at Fc, a sinewave at Fc+20kHz, and a sinewave at Fc-20kHz.
If Fc20kHz then one of the components becomes a "negative"
frequency. So the carrier must be greater than the baseband signal to
prevent this.

I'm afraid that this is not correct. The 'laws of physics' don't
suddenly stop working if the carrier is lower than the modulating
frequency. However, there's no need to get into complicated mathematics
to illustrate this. Here is a simple example:

(a) If you modulate a 10MHz carrier with a 1MHz signal, you will produce
two new signals (the sidebands) at the difference frequency of 10 minus
1 = 9MHz, and the sum frequency of 10 plus 1 = 11MHz. So you have the
original carrier at 10MHz, and sideband signals at 9 and 11MHz (with a
balanced modulator - no carrier - only 9 and 11MHz).

(b) If you modulate a 1MHz carrier with a 10MHz signal, you will produce
two new signals (the sidebands) at the difference frequency of 1 minus
10 = minus 9MHz, and the sum frequency of 1 plus 10 = 11MHz. The
implication of the negative 'minus 9' MHz signal is that the phase of
the 9MHz signal is inverted, ie 180 degrees out-of-phase from 9MHz
produced in (a). So you have the original carrier at 1MHz, and sidebands
at 9 and 11MHz (again, with a balanced modulator - no carrier - only 9
and 11MHz).

The waveforms of the full composite AM signals of (a) and (b) will look
quite different. The carriers are at different frequencies, and the
phase of the 9MHz signal is inverted. However, with a double-balanced
modulator, you will only have the 9 and 11MHz signal so, surprisingly,
the resulting signals of (a) and (b) will look the same.

[Note that, in practice, many double-balanced modulators/mixers put
loads of unwanted signals - mainly due the effects of harmonic mixing.
However, the basic 'laws of physics' still apply.]

Finally, although I have spoken with great authority, when I get a
chance I WILL be doing at test with a tobacco-tin double-balanced mixer,
a couple of signal generators and a spectrum analyser - just to make
sure that I'm not talking rubbish. In the meantime, I'm sure that some
will correct me if I'm wrong.

Ian.


Ian,

I believe your analysis is correct. But if you expect to build a
receiver that uses a filter centered at 1 MHz with a BW of 20+ MHz to
recover a DSB AM signal, I don't believe that the DBM approach will
accomplish this. With your approach, you could filter out the sidebands
by centering a filter around 10 MHz (the baseband freq). This could be
used to recover the baseband 10 MHz signal. But the OP asked about AM
of a carrier at very low frequencies. Good explanation of what happens
when using a DBM, though.

Regards,
-C

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

In article ,
cledus wrote:

Snip

Would you please have the decency to snip rec.radio.shortwave and other
groups from the newsgroup header. Thanks.

--
Telamon
Ventura, California

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"John Smith I" wrote in message
...
Listen to a "strong--pure am signal" on an fm receiver, turn up the volume
on the fm receiver, something is responsible for that ... repeat
experiment with the reverse ... "imperfect world theory" proof!

What is responsible for that is not that AM somehow also
produces FM, but simply that the type of demodulator used
by the FM receiver in question will also demodulate AM to
a usable degree. Ditto the reverse (look up "slope detection"
for an example of how a very common AM demodulator
can also demodulate FM).

Bob M.

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Jul 1, 10:06 pm, Telamon
wrote:
In article ,

cledus wrote:

Snip

- Would you please have the decency to snip
- rec.radio.shortwave and other groups from
- the newsgroup header. Thanks.
-
- --
- Telamon
- Ventura, California

Telamon,

Off-Topic + Cross-Posting -and- 'Decency'
http://en.wikipedia.org/wiki/Oxymoron
Wow - Now There Is A Real Oxymoron !

~ RHF

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
 

Jeff Liebermann wrote:

Watch antennas:
http://www.c-max-time.com/products/productsOverview.php?catID=5
See the photos of the various antennas. Too bad there's no specs.

I'll grind out the field strength numbers later. I've been living in
the microwave region for so long, that I'm having problems with LF
calcs.

http://www.c-max-time.com/downloads/getFile.php?id=423
Gives dimensions,No of turns,Inductance etc.

AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
 

On 7/1/07 10:06 PM, in article
,
"Telamon" wrote:

In article ,
cledus wrote:

Snip

Would you please have the decency to snip rec.radio.shortwave and other
groups from the newsgroup header. Thanks.

Would you please come and ask nicely. I don't like how you put your order.

AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
 

Jeff Liebermann wrote:

Conventional TV is VSB (visidual side band)


Vestigal Sideband


--
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

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

In message , Michael A. Terrell
writes
Jeff Liebermann wrote:

Conventional TV is VSB (visidual side band)


Vestigal Sideband


Better still, Vestigial Sideband!
--
Ian

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

kev hath wroth:

Jeff Liebermann wrote:

Watch antennas:
http://www.c-max-time.com/products/productsOverview.php?catID=5
See the photos of the various antennas. Too bad there's no specs.

I'll grind out the field strength numbers later. I've been living in
the microwave region for so long, that I'm having problems with LF
calcs.

http://www.c-max-time.com/downloads/getFile.php?id=423
Gives dimensions,No of turns,Inductance etc.

Thanks. I downloaded that yesterday and got a file with no extension.
I eventually figured out it's a PDF file and renamed it.

The site also has a rather sketchy article on antenna design at:
http://www.c-max-time.com/tech/antenna.php
I also found the chip sensitivity somewhere at
0.5uv typical
0.8uv max
with a field strength range of:
15-20 uV/m using a 10mm x 60 mm rod.

I'm currently slogging through the NIST web pile trying to find the
historical or estimated field strengths for the left coast area.
http://tf.nist.gov/timefreq/stations/lflibrary.htm
Ah, foundit:
http://tf.nist.gov/timefreq/general/pdf/1383.pdf
Table 2.4 shows signal strength in San Diego varying from 180 uV/m to
1000 uV/m. Now all I need to do is figure out how much S/N ratio is
required at the receiver input to properly decode the time signals.

All the information needed is probably there, scattered among an
assortment of documents, but I'm at a loss on how to estimate the
actual field strength sensitivity given the rod antenna
specifications. The formula #1 at:
http://www.c-max-time.com/tech/antenna.php
has all the right parameters, but I keep getting insane results when I
try to plug in real and estimated values. Maybe some coffee will
help.

I'll work on it more during the next few daze. It should be easy
(famous last words). However, paying work comes first.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"Michael A. Terrell" hath wroth:

Jeff Liebermann wrote:
Conventional TV is VSB (visidual side band)

Vestigal Sideband

Ummm... How about Vestigial Sideband instead?
http://www.javvin.com/hardware/VSB.html
http://whatis.techtarget.com/definition/0,,sid9_gci332235,00.html
The last vestige of spelling abilities disappeared long ago and was
replaced by a spellin chequer that lacked the term. Sorry.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Mon, 2 Jul 2007 16:41:01 +0100, Ian Jackson wrote:
In message , Michael A. Terrell
writes
Jeff Liebermann wrote:

Conventional TV is VSB (visidual side band)


Vestigal Sideband


Better still, Vestigial Sideband!

You're both wrong. It is VIRTUAL SIDEBAND because it isn't completely
real and the other sideband which isn't virtual carries the missing high
frequency modulation info. Once it gets into your second detector then
it becomes real due to the laws of product modulation.

Next, you will be telling people that VGA doesn't stand for "virtual
graphics array."

--
Posted via a free Usenet account from http://www.tarrnews.net

snip, Snip. SNIP ! the "Rec.Radio.Shortwave" Group from the Newsgroups {Distribution} Header - please, Please. PLEASE !
 

On Jul 2, 6:16 am, Don Bowey wrote:
On 7/1/07 10:06 PM, in article
,

"Telamon" wrote:
In article ,
cledus wrote:

Snip

Would you please have the decency to snip rec.radio.shortwave and other
groups from the newsgroup header. Thanks.

- Would you please come and ask nicely.
- I don't like how you put your order.

don bowey, Don Bowey. DON BOWEY !

Oh Please with Sugar and Spice and Everything Nice
snip, Snip. SNIP ! the "Rec.Radio.Shortwave" Group
from the Newsgroups {Distribution} Header when you
Post your Reply - It would be ever so decent of you
Kind and Wonder Sir. ;-)

thank you very much - most respectfully ~ RHF

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

In article ,
Don Bowey wrote:

On 7/1/07 10:06 PM, in article
,
"Telamon" wrote:

In article ,
cledus wrote:

Snip

Would you please have the decency to snip rec.radio.shortwave and other
groups from the newsgroup header. Thanks.

Would you please come and ask nicely. I don't like how you put your order.

This is a stupid cross posted Troll thread so pretty please with sugar
on it snip the other news groups it does not originate from. Thank you
very, very much in advance.

--
Telamon
Ventura, California

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Jul 2, 9:09 pm, Telamon
wrote:
In article ,
Don Bowey wrote:

On 7/1/07 10:06 PM, in article
,
"Telamon" wrote:

In article ,
cledus wrote:

Snip

Would you please have the decency to snip rec.radio.shortwave and other
groups from the newsgroup header. Thanks.

Would you please come and ask nicely. I don't like how you put your order.

This is a stupid cross posted Troll thread so pretty please with sugar
on it snip the other news groups it does not originate from. Thank you
very, very much in advance.

--
Telamon
Ventura, California

Bravo ! ;o} ~ RHF

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?
What would it look like on a spectrum analyzer?

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?
What would that look like on a spectrum analyzer?

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency
 

Ron Baker, Pluralitas! wrote:
"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?
What would it look like on a spectrum analyzer?

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?
What would that look like on a spectrum analyzer?

snip, Snip. SNIP ! the "Rec.Radio.Shortwave" Group from the Newsgroups {Distribution} Header - please, Please. PLEASE !
 

On Mon, 02 Jul 2007 14:42:49 -0700, RHF
wrote:

On Jul 2, 6:16 am, Don Bowey wrote:
On 7/1/07 10:06 PM, in article
,

"Telamon" wrote:
In article ,
cledus wrote:

Snip

Would you please have the decency to snip rec.radio.shortwave and other
groups from the newsgroup header. Thanks.

- Would you please come and ask nicely.
- I don't like how you put your order.

don bowey, Don Bowey. DON BOWEY !

Oh Please with Sugar and Spice and Everything Nice
snip, Snip. SNIP ! the "Rec.Radio.Shortwave" Group
from the Newsgroups {Distribution} Header when you
Post your Reply - It would be ever so decent of you
Kind and Wonder Sir. ;-)

thank you very much - most respectfully ~ RHF

---
Seems to me his posts are on topic for rrs, so why don't you just
learn how to use a filter?


--
JF

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"
wrote:


"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

---
LTSPICE circuit list:

Version 4
SHEET 1 1672 1576
WIRE 32 880 -256 880
WIRE 192 880 32 880
WIRE 528 912 336 912
WIRE 192 944 -112 944
WIRE -256 992 -256 880
WIRE -112 992 -112 944
WIRE -256 1120 -256 1072
WIRE -112 1120 -112 1072
WIRE -112 1120 -256 1120
WIRE -256 1168 -256 1120
FLAG -256 1168 0
FLAG 32 880 in
SYMBOL SPECIALFUNCTIONS\\MODULATE 192 880 R0
WINDOW 0 37 -55 Left 0
WINDOW 3 55 119 Center 0
SYMATTR InstName A1
SYMATTR Value mark=1e6 space=1e6
SYMBOL voltage -256 976 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 10
SYMBOL voltage -112 976 R0
WINDOW 3 24 160 Left 0
WINDOW 123 24 132 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(.5 .5 1e5)
SYMATTR Value2 AC 1
TEXT -96 1240 Left 0 !.tran 5e-5
TEXT -96 1208 Left 0 !.params w0=2*pi*1K Q=5

---

What would it look like on a spectrum analyzer?

---

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

---

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

---
LTSPICE circuit list:

Version 4
SHEET 1 880 680
WIRE 240 64 176 64
WIRE 432 64 320 64
WIRE 352 144 224 144
WIRE 352 160 352 144
WIRE 16 176 -208 176
WIRE 160 176 96 176
WIRE 176 176 176 64
WIRE 176 176 160 176
WIRE 320 176 176 176
WIRE 432 192 432 64
WIRE 432 192 384 192
WIRE 320 208 288 208
WIRE 288 256 288 208
WIRE 16 288 -48 288
WIRE 160 288 160 176
WIRE 160 288 96 288
WIRE 224 320 224 144
WIRE 352 320 352 224
WIRE -208 336 -208 176
WIRE -48 336 -48 288
WIRE -208 448 -208 416
WIRE -48 448 -48 416
WIRE -48 448 -208 448
WIRE 224 448 224 400
WIRE 224 448 -48 448
WIRE 352 448 352 400
WIRE 352 448 224 448
WIRE -208 496 -208 448
FLAG -208 496 0
FLAG 288 256 0
SYMBOL voltage -208 320 R0
WINDOW 0 -42 5 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value SINE(0 .1 1.1e6)
SYMBOL res 112 160 R90
WINDOW 0 -33 56 VBottom 0
WINDOW 3 -31 61 VTop 0
SYMATTR InstName R1
SYMATTR Value 1000
SYMBOL voltage -48 320 R0
WINDOW 0 -39 4 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 .1 .9e6)
SYMBOL res 112 272 R90
WINDOW 0 -38 56 VBottom 0
WINDOW 3 -31 59 VTop 0
SYMATTR InstName R2
SYMATTR Value 1000
SYMBOL res 336 48 R90
WINDOW 0 -36 59 VBottom 0
WINDOW 3 -36 61 VTop 0
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL voltage 352 416 R180
WINDOW 0 14 106 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 12
SYMBOL voltage 224 304 R0
WINDOW 0 -44 4 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value 12
SYMBOL Opamps\\UniversalOpamp 352 192 R0
SYMATTR InstName U2
TEXT -252 520 Left 0 !.tran 3e-5


Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

---

What would that look like on a spectrum analyzer?

---

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz


--
JF

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Jul 3, 12:50 pm, John Fields wrote:
On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

....Keith

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Jul 3, 2:07 pm, Keith Dysart wrote:
On Jul 3, 12:50 pm, John Fields wrote:





On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

...Keith-

Ooops. I misspoke. They are not quite the same.

The spectrum is the same, but if you want to get exactly
the same result, the lower frequency needs a 90 degree
offset and the upper frequency needs a -90 degree offset.

And the amplitudes of the the sum and difference
frequencies need to be one half of the amplitude of
the frequencies being multiplied.

....Keith

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Tue, 03 Jul 2007 12:05:52 -0700, Keith Dysart
wrote:

On Jul 3, 2:07 pm, Keith Dysart wrote:
On Jul 3, 12:50 pm, John Fields wrote:





On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

...Keith-

Ooops. I misspoke. They are not quite the same.

---
That's right. They can't possibly be because the first instance
_was_ multiplication and the second instance addition.
---

The spectrum is the same, but if you want to get exactly
the same result, the lower frequency needs a 90 degree
offset and the upper frequency needs a -90 degree offset.

---
That makes no sense since the frequencies are different and,
consequently, the phase difference between the signals will be
constantly changing.



--
JF

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Jul 3, 4:19 pm, John Fields wrote:
On Tue, 03 Jul 2007 12:05:52 -0700, Keith Dysart





wrote:
On Jul 3, 2:07 pm, Keith Dysart wrote:
On Jul 3, 12:50 pm, John Fields wrote:

On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

...Keith-

Ooops. I misspoke. They are not quite the same.

---
That's right. They can't possibly be because the first instance
_was_ multiplication and the second instance addition.

Quite counter intuitive, I agree, but none-the-less true.
To convince myself, I once created an Excel spreadsheet
to demonstrate the fact.

It along with some other discussion and plots are available
here http://keith.dysart.googlepages.com/radio5

The spectrum is the same, but if you want to get exactly
the same result, the lower frequency needs a 90 degree
offset and the upper frequency needs a -90 degree offset.

---
That makes no sense since the frequencies are different and,
consequently, the phase difference between the signals will be
constantly changing.

To get exactly the same results, if, at time t0, the phases
for the signals being multiplied together are 0, then at
time t0, the initial phases for the signals being added
must be 90 and -90.

....Keith

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Tue, 03 Jul 2007 15:02:59 -0700, Keith Dysart
wrote:

On Jul 3, 4:19 pm, John Fields wrote:
On Tue, 03 Jul 2007 12:05:52 -0700, Keith Dysart





wrote:
On Jul 3, 2:07 pm, Keith Dysart wrote:
On Jul 3, 12:50 pm, John Fields wrote:

On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

...Keith-

Ooops. I misspoke. They are not quite the same.

---
That's right. They can't possibly be because the first instance
_was_ multiplication and the second instance addition.

Quite counter intuitive, I agree, but none-the-less true.
To convince myself, I once created an Excel spreadsheet
to demonstrate the fact.

It along with some other discussion and plots are available
here http://keith.dysart.googlepages.com/radio5

The spectrum is the same, but if you want to get exactly
the same result, the lower frequency needs a 90 degree
offset and the upper frequency needs a -90 degree offset.

---
That makes no sense since the frequencies are different and,
consequently, the phase difference between the signals will be
constantly changing.

To get exactly the same results, if, at time t0, the phases
for the signals being multiplied together are 0, then at
time t0, the initial phases for the signals being added
must be 90 and -90.

---
OK, but that's just for the single slice in time where the circuit
reactances for both frequencies are complex conjugates, and cancel,
leaving only pure resistance for both signals to drive at that
instant.


--
JF

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

In article ,
John Fields wrote:

On Tue, 03 Jul 2007 12:05:52 -0700, Keith Dysart
wrote:

On Jul 3, 2:07 pm, Keith Dysart wrote:
On Jul 3, 12:50 pm, John Fields wrote:





On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

...Keith-

Ooops. I misspoke. They are not quite the same.

---
That's right. They can't possibly be because the first instance
_was_ multiplication and the second instance addition.
---

The spectrum is the same, but if you want to get exactly
the same result, the lower frequency needs a 90 degree
offset and the upper frequency needs a -90 degree offset.

---
That makes no sense since the frequencies are different and,
consequently, the phase difference between the signals will be
constantly changing.

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

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"isw" wrote in message
...

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

I can't speak to second harmonics of a received signal, though I can't think
why they would be any different than an internal signal.. but:

When you frequency multiply and FM signal in a transmitter (As used to be
done on most FM transmitters in the days before PLL came along), you not
only multiplied the extant frequency, but the modulation swing as well. i.e.
if you start with a 1 MHz FM modualated crystal oscillator, and manage to
get 500 Hz swing from the crystal (using this only as a simple example),
then if you double that signal's carrier frequency, you also double the FM
swing to 1 KHz. Tripling it from there would give you a 6 MHz carrier with a
3 KHz swing, and so on.

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

In message , Brenda Ann
writes

"isw" wrote in message
...

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

I can't speak to second harmonics of a received signal, though I can't think
why they would be any different than an internal signal.. but:

When you frequency multiply and FM signal in a transmitter (As used to be
done on most FM transmitters in the days before PLL came along), you not
only multiplied the extant frequency, but the modulation swing as well. i.e.
if you start with a 1 MHz FM modualated crystal oscillator, and manage to
get 500 Hz swing from the crystal (using this only as a simple example),
then if you double that signal's carrier frequency, you also double the FM
swing to 1 KHz. Tripling it from there would give you a 6 MHz carrier with a
3 KHz swing, and so on.


For multiplying FM, yes, of course, this is exactly what happens. And as
it happens for FM, it must also happen for AM.

However, I feel that the subject of the effects of harmonics of an AM
signal needs to be investigated. I think what you hear depends on how
and where the harmonic is produced, and the characteristics of the
receiver.

In the good old days of AM, on those occasions when I listened to the
2nd harmonic of my transmissions, I got the impression that the quality
of the audio was not very good, and that the mod depth was lower than on
the fundamental.

Assuming that the signal is coming from a 'normal' AM transmitter, you
could have two scenarios:

(a) In the first scenario, the signal is initially clean, but gets
multiplied by two, along with the sidebands. [This may occur in the
transmitter itself, or in the receiver, or in some external device.] In
this case, the frequencies and bandwidth of the sidebands will be
doubled (like FM multiplication). The signal should definitely be of
poor quality (it should sound rather 'toppy'), but may still be fairly
intelligible. If the bandwidth of the receiver is be insufficient to
embrace the full (doubled) bandwidth of the signal, you will only hear
the lower part of the audio spectrum. This will limit the toppiness, and
the level will be rather low, but, in practice, the signal quality may
be quite 'acceptable'.

(b) In the second scenario, the 2nd harmonic is effectively present
BEFORE modulation, so it gets modulated along with the fundamental. In
this case, the lower frequencies of sidebands of the 2nd harmonic will
be 'normal', and the signal will sound normal.

In practice, both (a) and (b) probably occur together (certainly in the
transmitter). Again, as the receiver will only select the lower part of
the audio spectrum, what you hear might sound OK. I suspect that, if you
'off-tune' a bit, you will find a lot of sideband 'splash' either side
of the signal.

It should not be difficult to set up a simulation of the above, and do
some quantitative tests. Any volunteers?

Ian.
--

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"Keith Dysart" wrote in message
ps.com...
On Jul 3, 2:07 pm, Keith Dysart wrote:
On Jul 3, 12:50 pm, John Fields wrote:





On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

...Keith-

Ooops. I misspoke. They are not quite the same.

The spectrum is the same, but if you want to get exactly
the same result, the lower frequency needs a 90 degree
offset and the upper frequency needs a -90 degree offset.

And the amplitudes of the the sum and difference
frequencies need to be one half of the amplitude of
the frequencies being multiplied.

...Keith


You win. :)

When I conceived the problem I was thinking
cosines actually. In which case there are no
phase shifts to worry about in the result.

I also forgot the half amplitude factor.

While it might not be obvious, the two cases I
described are basically identical. And this
situation occurs in real life, i.e. in radio signals,
oceanography, and guitar tuning.

It follows from what is taught in high school
geometry.

cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b])

Basically: multiplying two sine waves is
the same as adding the (half amplitude)
sum and difference frequencies.

(For sines it is
sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b])
= 0.5 * (sin[a-b+90degrees] - sin[a+b+90degrees])
= 0.5 * (sin[a-b+90degrees] + sin[a+b-90degrees])
)

--
rb

AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
 

On 7/4/07 7:52 AM, in article , "Ron
Baker, Pluralitas!" wrote:


"Keith Dysart" wrote in message
ps.com...
On Jul 3, 2:07 pm, Keith Dysart wrote:
On Jul 3, 12:50 pm, John Fields wrote:





On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

...Keith-

Ooops. I misspoke. They are not quite the same.

The spectrum is the same, but if you want to get exactly
the same result, the lower frequency needs a 90 degree
offset and the upper frequency needs a -90 degree offset.

And the amplitudes of the the sum and difference
frequencies need to be one half of the amplitude of
the frequencies being multiplied.

...Keith


You win. :)

When I conceived the problem I was thinking
cosines actually. In which case there are no
phase shifts to worry about in the result.

I also forgot the half amplitude factor.

While it might not be obvious, the two cases I
described are basically identical. And this
situation occurs in real life, i.e. in radio signals,
oceanography, and guitar tuning.

It follows from what is taught in high school
geometry.

cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b])

Basically: multiplying two sine waves is
the same as adding the (half amplitude)
sum and difference frequencies.

No, they aren't the same at all, they only appear to be the same before
they are examined. The two sidebands will not have the correct phase
relationship.

One could, temporarily, mistake the added combination for a full carrier
with independent sidebands, however.




(For sines it is
sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b])
= 0.5 * (sin[a-b+90degrees] - sin[a+b+90degrees])
= 0.5 * (sin[a-b+90degrees] + sin[a+b-90degrees])
)

--
rb

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

In article ,
Ian Jackson wrote:

In message , Brenda Ann
writes

"isw" wrote in message
...

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

I can't speak to second harmonics of a received signal, though I can't think
why they would be any different than an internal signal.. but:

When you frequency multiply and FM signal in a transmitter (As used to be
done on most FM transmitters in the days before PLL came along), you not
only multiplied the extant frequency, but the modulation swing as well. i.e.
if you start with a 1 MHz FM modualated crystal oscillator, and manage to
get 500 Hz swing from the crystal (using this only as a simple example),
then if you double that signal's carrier frequency, you also double the FM
swing to 1 KHz. Tripling it from there would give you a 6 MHz carrier with a
3 KHz swing, and so on.


For multiplying FM, yes, of course, this is exactly what happens. And as
it happens for FM, it must also happen for AM.

If you start with, say, a 1 MHz carrier AM modulated at 1 KHz, tuning to
the second harmonic gives you a 2 MHz carrier AM modulated at 1 KHz; not
2 KHz as your "must also happen for AM" would suggest.

Isaac

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

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

"Keith Dysart" wrote in message
ps.com...
On Jul 3, 2:07 pm, Keith Dysart wrote:
On Jul 3, 12:50 pm, John Fields wrote:





On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

...Keith-

Ooops. I misspoke. They are not quite the same.

The spectrum is the same, but if you want to get exactly
the same result, the lower frequency needs a 90 degree
offset and the upper frequency needs a -90 degree offset.

And the amplitudes of the the sum and difference
frequencies need to be one half of the amplitude of
the frequencies being multiplied.

...Keith


You win. :)

When I conceived the problem I was thinking
cosines actually. In which case there are no
phase shifts to worry about in the result.

I also forgot the half amplitude factor.

While it might not be obvious, the two cases I
described are basically identical. And this
situation occurs in real life, i.e. in radio signals,
oceanography, and guitar tuning.

The beat you hear during guitar tuning is not modulation; there is no
non-linear process involved (i.e. no multiplication).

Isaac

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

In article ,
Ian Jackson wrote:

(b) In the second scenario, the 2nd harmonic is effectively present
BEFORE modulation, so it gets modulated along with the fundamental. In
this case, the lower frequencies of sidebands of the 2nd harmonic will
be 'normal', and the signal will sound normal.

I believe that will be the likely scenario for any AM transmitter
which uses plate modulation or a similar "high level modulation"
system. If the RF finals are running in a single-ended configuration
(rather than push-pull) even the unmodulated carrier is likely to have
a significant amount of second-harmonic distortion in it... and I'd
think that this would tend to grow worse as the audio peaks push the
finals up towards their maximum output power.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"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

AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
 

"Don Bowey" wrote in message
...
On 7/4/07 7:52 AM, in article ,
"Ron
Baker, Pluralitas!" wrote:

snip


cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b])

Basically: multiplying two sine waves is
the same as adding the (half amplitude)
sum and difference frequencies.

No, they aren't the same at all, they only appear to be the same before
they are examined. The two sidebands will not have the correct phase
relationship.

What do you mean? What is the "correct"
relationship?


One could, temporarily, mistake the added combination for a full carrier
with independent sidebands, however.




(For sines it is
sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b])
= 0.5 * (sin[a-b+90degrees] - sin[a+b+90degrees])
= 0.5 * (sin[a-b+90degrees] + sin[a+b-90degrees])
)

--
rb

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

"isw" wrote in message
...
In article ,
"Ron Baker, Pluralitas!" wrote:

"Keith Dysart" wrote in message
ps.com...
On Jul 3, 2:07 pm, Keith Dysart wrote:
On Jul 3, 12:50 pm, John Fields wrote:





On Mon, 2 Jul 2007 23:03:36 -0700, "Ron Baker, Pluralitas!"

wrote:

"John Smith I" wrote in message
...
Radium wrote:

snip

Suppose you have a 1 MHz sine wave whose amplitude
is multiplied by a 0.1 MHz sine wave.
What would it look like on an oscilloscope?

snip

What would it look like on a spectrum analyzer?

| |
| | | |
--------+--------------------+-------+------+----
100kHz 0.9MHz 1MHz 1.1MHz

Then suppose you have a 1.1 MHz sine wave added
to a 0.9 MHz sine wave.
What would that look like on an oscilloscope?

snip

Tricky!!!

It looks like AM but it isn't, it's just the phases sliding past
each other slowly and algebraically adding which creates the
illusion.

What would that look like on a spectrum analyzer?

| |
| |
-----------------------------+--------------+----
0.9MHz 1.1MHz

--
JF

But if you remove the half volt bias you put on the
100 kHz signal in the multiplier version, the results
look exactly like the summed version, so I suggest
that results are the same when a 4 quadrant multiplier
is used.

And since the original request was for a "1 MHz sine
wave whose amplitude is multiplied by a 0.1 MHz sine
wave" I think a 4 quadrant multiplier is in order.

...Keith-

Ooops. I misspoke. They are not quite the same.

The spectrum is the same, but if you want to get exactly
the same result, the lower frequency needs a 90 degree
offset and the upper frequency needs a -90 degree offset.

And the amplitudes of the the sum and difference
frequencies need to be one half of the amplitude of
the frequencies being multiplied.

...Keith


You win. :)

When I conceived the problem I was thinking
cosines actually. In which case there are no
phase shifts to worry about in the result.

I also forgot the half amplitude factor.

While it might not be obvious, the two cases I
described are basically identical. And this
situation occurs in real life, i.e. in radio signals,
oceanography, and guitar tuning.

The beat you hear during guitar tuning is not modulation; there is no
non-linear process involved (i.e. no multiplication).

Isaac

In short, the human auditory system is not linear.
It has a finite resolution bandwidth. It can't resolve
two tones separted by a few Hertz as two separate tones.
(But if they are separted by 100 Hz they can easily
be separated without hearing a beat.)

The same affect can be seen on a spectrum analyzer.
Give it two frequencies separated by 1 Hz. Set the
resolution bandwidth to 10 Hz. You'll see the peak
rise and fall at 1 Hz.

AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency
 

On Wed, 04 Jul 2007 09:11:58 -0700, isw wrote:

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

You win. :)

When I conceived the problem I was thinking
cosines actually. In which case there are no
phase shifts to worry about in the result.

I also forgot the half amplitude factor.

While it might not be obvious, the two cases I
described are basically identical. And this
situation occurs in real life, i.e. in radio signals,
oceanography, and guitar tuning.

The beat you hear during guitar tuning is not modulation; there is no
non-linear process involved (i.e. no multiplication).

---
That's not true.

The human ear has a logarithmic amplitude response and the beat note
(the difference frequency) is generated there. The sum frequency is
too, but when unison is achieved it'll be at precisely twice the
frequency of either fundamental and won't be noticed.


--
JF

AM electromagnetic waves: 20 KHz modulation frequency onanastronomically-low carrier frequency
 

On 7/4/07 10:16 AM, in article ,
"Ron Baker, Pluralitas!" wrote:


"Don Bowey" wrote in message
...
On 7/4/07 7:52 AM, in article ,
"Ron
Baker, Pluralitas!" wrote:

snip


cos(a) * cos(b) = 0.5 * (cos[a+b] + cos[a-b])

Basically: multiplying two sine waves is
the same as adding the (half amplitude)
sum and difference frequencies.

No, they aren't the same at all, they only appear to be the same before
they are examined. The two sidebands will not have the correct phase
relationship.

What do you mean? What is the "correct"
relationship?


One could, temporarily, mistake the added combination for a full carrier
with independent sidebands, however.




(For sines it is
sin(a) * sin(b) = 0.5 * (cos[a-b]-cos[a+b])
= 0.5 * (sin[a-b+90degrees] - sin[a+b+90degrees])
= 0.5 * (sin[a-b+90degrees] + sin[a+b-90degrees])
)

--
rb





When AM is correctly accomplished (a single voiceband signal is modulated
onto a carrier via a non-linear process), at an envelope detector the two
sidebands will be additive. But if you independe ntly place a carrier at
frequency ( c ), another carrier at ( c-1 khz) and another carrier at (c+ 1
kHz), the composite can look like an AM signal, but it is not, and only by
the most extreme luck will the sidebands be additive at the detector. They
would probably cycle between additive and subtractive since they have no
real relationship and were not the result of amplitude modulation.

AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency
 

When AM is correctly accomplished (a single voiceband signal is modulated
onto a carrier via a non-linear process), at an envelope detector the two
sidebands will be additive. But if you independe ntly place a carrier at
frequency ( c ), another carrier at ( c-1 khz) and another carrier at (c+
1 kHz), the composite can look like an AM signal, but it is not, and only
by
the most extreme luck will the sidebands be additive at the detector.
They would probably cycle between additive and subtractive since they have
no real relationship and were not the result of amplitude modulation.

A peak detector is best understood in the time domain, try to create a
simple description in the frequency domain and you can only cause confusion
and incorrect conclusions.