rf design

D

deaks

Guest
Hi,
Here's my question.
If you have an A.M. transmitter (power is extremely small) and you
superimpose a signal unto the carrier, then detect the signal at a
distance X, could you make it so that the amplitude of the
superimposed signal be variable to distance?
So the farther you go, the weaker the signal gets. Its okay to amplify
the carrier in the reciever but not the superimposed one, if you get
what i'm saying.
So in essence, the carried signal may or may not have fallen off due
to distance and the spread (1/r(sq) ?).

What do you guys think?

Deaks
 
deaks wrote:
If you have an A.M. transmitter (power is extremely small) and you
superimpose a signal unto the carrier, then detect the signal at a
distance X, could you make it so that the amplitude of the
superimposed signal be variable to distance?
Click to expand...
It would help if you used standard terminology.
By "superimpose a signal unto the carrier" do you mean modulate the carrier
with the signal?
By "amplitude of the superimposed signal" do you mean modulation depth?

So the farther you go, the weaker the signal gets. Its okay to amplify
the carrier in the reciever but not the superimposed one, if you get
what i'm saying.
So in essence, the carried signal may or may not have fallen off due
to distance and the spread (1/r(sq) ?).
Click to expand...
I'm not sure what you mean but the modulation depth cannot vary with
distance, if that's what you're asking.
 
On 17 Nov 2004 11:55:09 -0800, deaks wrote:

Hi,
Here's my question.
If you have an A.M. transmitter (power is extremely small) and you
superimpose a signal unto the carrier, then detect the signal at a
distance X, could you make it so that the amplitude of the
superimposed signal be variable to distance?
So the farther you go, the weaker the signal gets. Its okay to amplify
the carrier in the reciever but not the superimposed one, if you get
what i'm saying.
So in essence, the carried signal may or may not have fallen off due
to distance and the spread (1/r(sq) ?).

What do you guys think?

Well, think about it. If the carrier is reduced by half over
Click to expand...
distance, it stands to reason that the modulated part will also -
you don't have to "make it so...". It'll still have the same %
modulation, though.

--
Best Regards,
Mike
 
On 17 Nov 2004 11:55:09 -0800, deakie@gmail.com (deaks) wroth:

Hi,
Here's my question.
If you have an A.M. transmitter (power is extremely small) and you
superimpose a signal unto the carrier, then detect the signal at a
distance X, could you make it so that the amplitude of the
superimposed signal be variable to distance?
So the farther you go, the weaker the signal gets. Its okay to amplify
the carrier in the reciever but not the superimposed one, if you get
what i'm saying.
So in essence, the carried signal may or may not have fallen off due
to distance and the spread (1/r(sq) ?).

What do you guys think?

Deaks
Click to expand...
Keep your day job.

Jim
 
Active8 <reply2group@ndbbm.net> wrote in message news:<101jn2p82ihfn$.dlg@news.individual.net>...
On 17 Nov 2004 11:55:09 -0800, deaks wrote:

Hi,
Here's my question.
If you have an A.M. transmitter (power is extremely small) and you
superimpose a signal unto the carrier, then detect the signal at a
distance X, could you make it so that the amplitude of the
superimposed signal be variable to distance?
So the farther you go, the weaker the signal gets. Its okay to amplify
the carrier in the reciever but not the superimposed one, if you get
what i'm saying.
So in essence, the carried signal may or may not have fallen off due
to distance and the spread (1/r(sq) ?).

What do you guys think?

Well, think about it. If the carrier is reduced by half over
distance, it stands to reason that the modulated part will also -
you don't have to "make it so...". It'll still have the same %
modulation, though.
Click to expand...

Thanks Mike, i'm not an rf engineer so I wasn't sure. I do realise
that the carrier itself would be reduced, and so to some extent, the
'modulated'(for the correct term?) signal would also be reduced. You
have cleared up the fact that its a percentage/ratio.
Ok, so now what I ask is this.....If the carrier is captured using a
more narrow filter set, and the modulated product, when
extracted....wouldn't it tend to be more or less dependent 'more' on
the distance issue than the carrier itself? Simply due to the fact
that the recieving circuit is more tuned to the carrier than the
modulated (AM) product....
I'm trying to avoid the amplification of the modulated signal as you
would get in a tank circuit......Do you see what i'm saying?
Thanks for all the comments so far......
 
On 18 Nov 2004 02:15:19 -0800, deakie@gmail.com (deaks) wrote:

Thanks Mike, i'm not an rf engineer so I wasn't sure. I do realise
that the carrier itself would be reduced, and so to some extent, the
'modulated'(for the correct term?) signal would also be reduced. You
have cleared up the fact that its a percentage/ratio.
Ok, so now what I ask is this.....If the carrier is captured using a
more narrow filter set, and the modulated product, when
extracted....wouldn't it tend to be more or less dependent 'more' on
the distance issue than the carrier itself? Simply due to the fact
that the recieving circuit is more tuned to the carrier than the
modulated (AM) product....
I'm trying to avoid the amplification of the modulated signal as you
would get in a tank circuit......Do you see what i'm saying?
Click to expand...
Nope.
Are you Kevin Aylward posting under an assumed name?
--

"What is now proved was once only imagin'd." - William Blake, 1793.
 
Mike posted:

(big snip)

<< Yeah, but amplifying the whole channel is cheaper and easier than trying to
reject the info content which is in the sidebands. As the
carrier is modulated, it decreases in level and the sidebands contain the
energy of the information. So you'd be trying to detect
something with less energy, i.e., whatever remains in the narrow BW you're
looking at.
I believe you are doing better than me at sorting out what the OP is after, but
I see you are confused about AM.

Through the AM modulation process, the average carrier amplitude remains
constant; the carrier level is not reduced. For 100% modulation you use 1 unit
of carrier signal, and 1/2 unit of modulating signal. The composite
transmitted signal is: 1 unit of carrier, 1/4 unit of lower sideband, and 1/4
unit of upper sideband.

Don
 
On 18 Nov 2004 16:06:30 GMT, Dbowey wrote:

Mike posted:

(big snip)

Yeah, but amplifying the whole channel is cheaper and easier than trying to
reject the info content which is in the sidebands. As the
carrier is modulated, it decreases in level and the sidebands contain the
energy of the information. So you'd be trying to detect
something with less energy, i.e., whatever remains in the narrow BW you're
looking at.


I believe you are doing better than me at sorting out what the OP is after, but
I see you are confused about AM.

Through the AM modulation process, the average carrier amplitude remains
constant; the carrier level is not reduced. For 100% modulation you use 1 unit
of carrier signal, and 1/2 unit of modulating signal. The composite
transmitted signal is: 1 unit of carrier, 1/4 unit of lower sideband, and 1/4
unit of upper sideband.
Click to expand...
Ok. It's FM where the carrier reduces.

--
Best Regards,
Mike
 
Have you thought of an RF signal starting a timer and then timing an
ultrasonic pulse travel time to get the distance? I am assuming it is 20
meters of open space, of course....

"deaks" <deakie@gmail.com> wrote in message
news:75a6bbf8.0411171155.5204a188@posting.google.com...
Hi,
Here's my question.
If you have an A.M. transmitter (power is extremely small) and you
superimpose a signal unto the carrier, then detect the signal at a
distance X, could you make it so that the amplitude of the
superimposed signal be variable to distance?
So the farther you go, the weaker the signal gets. Its okay to amplify
the carrier in the reciever but not the superimposed one, if you get
what i'm saying.
So in essence, the carried signal may or may not have fallen off due
to distance and the spread (1/r(sq) ?).

What do you guys think?

Deaks
Click to expand...
 
ok, Thanks Mike.
I thinks its time to build and test.
Thanks for all the help.
Deaks.
 
On Wed, 17 Nov 2004 22:36:55 -0000, deaks wrote:

Well, good luck with wtf you're up to, but I still think that if the
Rx tank is too tight (hi Q) that the information will be destroyed.
I'd just canabalize a cheap AM/FM radio and keep the Tx power very
low for your app. You can probably tweak one for the free band down
below AM b'cast, IIRC.

--
Best Regards,
Mike
 
On Fri, 19 Nov 2004 01:25:10 GMT, Rich Grise wrote:

<>
If you look at each respective signal on a spectrum analyzer, then with
AM, the carrier pip stays the same height, and the sidebands are a little
audiophool equalizer display. When you look at an FM signal on a spectrum
analyzer, the sidebands bear a very arcane relationship to the modulation,
and the carrier bounces up and down. With AM, the modulation adds energy,
with FM, it just moves it around.
Click to expand...
Three sentences. You win.
Looking at the spectrum of a radar-style pulse is very interesting too,
and until you've seen the output of a serrodyne-modulated TWAT,
Click to expand...
LOL. Please elaborate.

you
wouldn't believe me if I told you what it looks like, and it almost
can't be described in words anyway. )-; But it looks way neat!

Pictures!
Click to expand...
--
Best Regards,
Mike
 
deakie@gmail.com (deaks) wrote in message news:<75a6bbf8.0411171155.5204a188@posting.google.com>...
Hi,
Here's my question.
If you have an A.M. transmitter (power is extremely small) and you
superimpose a signal unto the carrier, then detect the signal at a
distance X, could you make it so that the amplitude of the
superimposed signal be variable to distance?
So the farther you go, the weaker the signal gets. Its okay to amplify
the carrier in the reciever but not the superimposed one, if you get
what i'm saying.
So in essence, the carried signal may or may not have fallen off due
to distance and the spread (1/r(sq) ?).

What do you guys think?

Deaks
Click to expand...
An AM carrier is not going to be a plausible method of detecting
distance by any means. With so many competing noise sources, inverse
square law, and reflection / absorption, besides your idea of using a
tuned tank is going to fall short of an accurate means of detection.
If you are not familiar with antenna design and bode plots, your
radiation pattern is going to b a big part of the design. The only
accurate way to be somewhat accurate is to measure time of flight of a
very narrow high frequency pulse train. I have done this in pulsed
radar ten years ago between an interrogator and a remote transponder
and it can be done with low level pulsed ultrasonics,laser and P.A.M.
pulse amplitude modulate RF.

There is considerable prior art in this area and you will only find
"time of flight" methodology not carrier attenuation as it is not an
acceptable means of measuring distance at all.
 
"Brian" <brian@w3gate.com> wrote in message news:<eeudnYTtE7S4-QDcRVn-jA@centurytel.net>...
Have you thought of an RF signal starting a timer and then timing an
ultrasonic pulse travel time to get the distance? I am assuming it is 20
meters of open space, of course....
Click to expand...

Actually Brian, i did think of ultrasonics but its more often going to
be an enclosed room or space.
I'm also toying with reflective surfaces and infrared but in terms of
costs and number of parts.....rf seems to be the way to go......
I'll just have to see how well it works out first.
thanks for the input....
Deaks
 
On 19 Nov 2004 17:27:06 GMT, Dbowey wrote:

Active8 posted:
snip
Ok. It's FM where the carrier reduces.

---
No, with FM the carrier _never_ intentionally varies in amplitude;
information is impressed on it by changing its frequency.

How should I restate my thought? The freq isn't fixed at center
channel when modulated. An SLM will show a constant "carrier"
though, because of averaging.

-- The spectral energy redistributes away from center freq. Is that
better?

Now I know that I can pull the analysis out and it shows
mathematically how the energy "moves" out into the sidebands from
the carrier. The analysis is done with a Bessel function.



Are you now commenting on AM or FM?

FM
Click to expand...


--
Best Regards,
Mike
 
On Fri, 19 Nov 2004 06:39:21 -0500, Active8 wrote:

On Thu, 18 Nov 2004 16:01:11 -0600, John Fields wrote:

On Thu, 18 Nov 2004 16:27:03 -0500, Active8 <reply2group@ndbbm.net
wrote:

On 18 Nov 2004 16:06:30 GMT, Dbowey wrote:

Mike posted:

(big snip)

Yeah, but amplifying the whole channel is cheaper and easier than trying to
reject the info content which is in the sidebands. As the
carrier is modulated, it decreases in level and the sidebands contain the
energy of the information. So you'd be trying to detect
something with less energy, i.e., whatever remains in the narrow BW you're
looking at.


I believe you are doing better than me at sorting out what the OP is after, but
I see you are confused about AM.

Through the AM modulation process, the average carrier amplitude remains
constant; the carrier level is not reduced. For 100% modulation you use 1 unit
of carrier signal, and 1/2 unit of modulating signal. The composite
transmitted signal is: 1 unit of carrier, 1/4 unit of lower sideband, and 1/4
unit of upper sideband.


Ok. It's FM where the carrier reduces.

---
No, with FM the carrier _never_ intentionally varies in amplitude;
information is impressed on it by changing its frequency.

How should I restate my thought? The freq isn't fixed at center
channel when modulated. An SLM will show a constant "carrier"
though, because of averaging.
Click to expand...
It sounds like John is just talking about looking at the waveform
on a scope. The FM is straight across the top and bottom, the
AM has humps.

Naturally, when you transform to the frequency domain, things
look a little different. ;-)

Cheers!
RIch
 
On Sat, 20 Nov 2004 00:42:09 GMT, Rich Grise <rich@example.net> wrote:


It sounds like John is just talking about looking at the waveform
on a scope. The FM is straight across the top and bottom, the
AM has humps.
Click to expand...
---
What I'm talking about is what happens to a carrier when it's
frequency modulated. Its amplitude doesn't change, its frequency
does. Take a look at an FM final sometime and you'll see that it's
running class C, and balls-to-the-wall, and if its amplitude changes
at all, it's incidental and certainly not intentional. Think about
why it's called carrier "deviation". It's because the modulation
causes the carrier frequency to deviate about its unmodulated center
frequency, and the depth of modulation is set by causing, for a
particular amplitude variation of the modulating signal, a particular
variation in the carrier frequency.
---

Naturally, when you transform to the frequency domain, things
look a little different. ;-)
Click to expand...
---
Platitudes...
 
Give info on exact environment. I don't see RF working well for any accuracy
what so ever. Having worked with RF area monitors (which worked poorly, too)
that tried the same technique, I would agrre time-of-flight is the best
option..

"deaks" <deakie@gmail.com> wrote in message
news:75a6bbf8.0411190115.48f27852@posting.google.com...
ok, Thanks Mike.
I thinks its time to build and test.
Thanks for all the help.
Deaks.
Click to expand...
 
On Thu, 18 Nov 2004 16:27:03 -0500, Active8 <reply2group@ndbbm.net>
wrote:

On 18 Nov 2004 16:06:30 GMT, Dbowey wrote:

Mike posted:

(big snip)

Yeah, but amplifying the whole channel is cheaper and easier than trying to
reject the info content which is in the sidebands. As the
carrier is modulated, it decreases in level and the sidebands contain the
energy of the information. So you'd be trying to detect
something with less energy, i.e., whatever remains in the narrow BW you're
looking at.


I believe you are doing better than me at sorting out what the OP is after, but
I see you are confused about AM.

Through the AM modulation process, the average carrier amplitude remains
constant; the carrier level is not reduced. For 100% modulation you use 1 unit
of carrier signal, and 1/2 unit of modulating signal. The composite
transmitted signal is: 1 unit of carrier, 1/4 unit of lower sideband, and 1/4
unit of upper sideband.


Ok. It's FM where the carrier reduces.
Click to expand...
---
No, with FM the carrier _never_ intentionally varies in amplitude;
information is impressed on it by changing its frequency.

--
John Fields
 
On Fri, 19 Nov 2004 06:41:11 -0500, Active8 wrote:

On Fri, 19 Nov 2004 01:25:10 GMT, Rich Grise wrote:



If you look at each respective signal on a spectrum analyzer, then with
AM, the carrier pip stays the same height, and the sidebands are a little
audiophool equalizer display. When you look at an FM signal on a spectrum
analyzer, the sidebands bear a very arcane relationship to the modulation,
and the carrier bounces up and down. With AM, the modulation adds energy,
with FM, it just moves it around.

Three sentences. You win.

Looking at the spectrum of a radar-style pulse is very interesting too,
and until you've seen the output of a serrodyne-modulated TWAT,

LOL. Please elaborate.

you
wouldn't believe me if I told you what it looks like, and it almost
can't be described in words anyway. )-; But it looks way neat!

Pictures!
Click to expand...
It's classified! Well, it was when I saw it in the USAF.

OK, anyway. You've got this "jamming package," which is a spectrum
display of noise through a fairly sharp, single-pole BPF - your
normal bell-curve, but with the aspect ratio of a villus.

When you apply the serrodyne modulation, (that's actually a variable-
freq. sawtooth applied to one of the accelerator electrodes in a TWT)
the package kind of "clones" itself. A copy appears right on top
of the existing package, then starts slowly moving to one side, getting
smaller like the e^(-t) curve, while the main one stays. This fools the
hell out of doppler radar.

The outline of a pulse spectrum is just the harmonics in the pulse,
which I was kinda surprised to see the outline looks like the path
of that classical bouncing ball. As the pulse width decreases, the
lobes get narrower and denser, and when it increases, the lobes get
wider and sparser until at 50%, it's the harmonics of a square wave.

http://dependability.cs.virginia.edu/bibliography/Schleher526-ch04.pdf
This guy's got some neat pix, but his serrodyne on p. 56 doesn't
show the side lobe moving.

And I've stumbled on an iconoclastic site, so TTFN. :)

Hope This Helps!
Rich
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top