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Old February 21st 06, 10:04 PM posted to rec.radio.cb
james
 
Posts: n/a
Default Cobra 25LTD Classic tune up

On Tue, 21 Feb 2006 04:24:38 -0800, Jay in the Mojave
wrote:

+james wrote:
+
+ On Sun, 19 Feb 2006 15:40:53 -0800, Jay in the Mojave
+ wrote:
+
+
++Hello All:
++
++I am hearing that many guys are addeding in another modulation IC, and
++Modulation transformer to double the audio power, allowing a higher
++carrier power to be 100% modulated.
++
++Jay in the Mojave
+
+
+ ******
+ The carrier in Double Sideband Full Carrier Amplitude Modulation
+ should remain constant during modulation. If not, then you have a far
+ greater problem.
+
+ james
+
+Hello James:
+
+No thats not how AM works. The Modulation increases and decreses the
+amptitude during Modulation. Thats how double sidband full modulation
+works. Look in a old ARRL Book.
+
+
+Jay in the Mojave

*****

I think you need to go back and reread and comprehend what those old
ARRL handbooks say. Then m aybe I suggest a good university textbook
on Communications. Oh by the way you may want to brush up on y our
Calculus and Differential Equations at the same time.

AM(t) = f(t)*cos(wc*t) + A*cos(wc*t)

where AM(t) is your Amplitude modulated signal with respect to time.
f(t) is the function that mathematically describes the modulating
frequency.
wc is the carrier frequency
t is time
A is amplitude

Taking the Fourier Transform of the carrier portion (A*cos(wc*t)
yields an impulse function with amplitude A at frequency wc. The rest
of the equation is your double sideband suppressed carrier and when
the Fourier transform of this is taken it will yield a frequency that
is the audio frequency plus and minus the carrier frequency at
amplitude of half the audio power.

I hope that this helps in your understanding of what Double Sideband
Full Carrier Amplitude modulation, more commonly called AM, is.

james

  #12   Report Post  
Old February 21st 06, 10:41 PM posted to rec.radio.cb
Dr.Death
 
Posts: n/a
Default Cobra 25LTD Classic tune up

wrote in message
...
Are you crazy... that unit can be made to have tremendous modulation.

Professor
www.telstar-electronics.com


BZZZT! Wrong....Keyclowns are not allowed to modify their radios.


But we will anyway.


  #13   Report Post  
Old February 21st 06, 10:48 PM posted to rec.radio.cb
Dr.Death
 
Posts: n/a
Default Cobra 25LTD Classic tune up

"Scott in Baltimore" wrote in message
...
Programbo wrote:
They sound like crap stock..No modulation..With a 2 pill it would still
sound like crap just much louder


OK. I've got one on the shelf. I don't use AM only radios.
I know it works. I tried it once.

Anybody make an offer for it. Shipping would be actual postage from 212..

I should clean up this Uniden PC76XL and get that off my shelf, too.
Also a TRC-422 and a TRC-422A just sits and sits.

I'm not sure if I should sell the Regency Range Gain, Lafayette LMS-40,
Midland 76-858, and forget about my 2950.

I spent good money on the LMS-40 to get it repaired because some dork
had tried to put extra channels in it and had really butchered it.
I'd have to sell that one for at least $100. It's in good shape
externally.

I also have a lightning struck 148GTL. The owner said it's DOA.
I'm not going to bother testing it. His A99 was toothpicks in the yard!

DONTSPAMME is every other letter in my email addy. Remove that to reply.
Serious inquiries only. Leave a phone number in the email for call back
and give a time referenced to a timezone to call on my dime.


What does the case and face plate look like. My 148 could use some cosmetic
surgery.


  #14   Report Post  
Old February 22nd 06, 04:02 AM posted to rec.radio.cb
Frank Gilliland
 
Posts: n/a
Default Cobra 25LTD Classic tune up

On Tue, 21 Feb 2006 12:29:25 -0500, Scott in Baltimore
wrote in
:

******
The carrier in Double Sideband Full Carrier Amplitude Modulation
should remain constant during modulation. If not, then you have a far
greater problem.
james



Hello James:

No thats not how AM works. The Modulation increases and decreses the
amptitude during Modulation. Thats how double sidband full modulation
works. Look in a old ARRL Book.


Jay in the Mojave


Jay, I respectfully disagree.

An AM carrier doesn't change, just sidebands are added in the mixing (modulation)
process, and the instantaneous voltage shown on an o-scope will be 4 times greater
then the carrier power itself. Since the audio added is 50% of the carrier, the
RMS power will be 150% of the unmodulated carrier. The peak to peak voltage is
greater. Put a 1000 Hz tone on a signal and look at it on spec-an.

(make sure to do this test with an unmodified radio, "swing kits" ruin proper AM)



It's about time to put this argument to rest...... you're both right.
The amplitude of the -signal- changes according to the modulation, but
the -carrier- is steady. The difference is that the signal (as seen on
an o-scope) is the vector sum of the carrier and the sidebands, while
the -carrier- (as seen on the spectrum analyzer) is only an isolated
component of the total signal.

Does that clear things up a bit?







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  #15   Report Post  
Old February 22nd 06, 06:34 AM posted to rec.radio.cb
ron
 
Posts: n/a
Default Cobra 25LTD Classic tune up

cut D9 for modulation, adjust L10, L9, L8 for power.


"Programbo" wrote in message
oups.com...
I have an old (Aug 1991) 25 LTD Classic someone just gave me and it all
works except it`s just factory stock in everyway and doesn`t put out
worth a damn...I`ve been away from the game so long I`ve lost all my
notes on the various tricks to tune it up beyond swapping out the final
and driver..Clip this..change that...?...Maybe some of the old timers
who remember me and know I`m cool can lend a hand..Send me an e-mail if
you want to avoid the trolls who`ll turn this into an anti-keyclown
thread






  #16   Report Post  
Old February 22nd 06, 01:15 PM posted to rec.radio.cb
Dr.Death
 
Posts: n/a
Default Cobra 25LTD Classic tune up

"ron" wrote in message
om...
cut D9 for modulation, adjust L10, L9, L8 for power.


Do NOT cut D9 or it will sound like ****. Instead using a scope adjust VR5
until it starts to clip and back it off a hair.


  #18   Report Post  
Old February 24th 06, 01:49 AM posted to rec.radio.cb
Programbo
 
Posts: n/a
Default Cobra 25LTD Classic tune up

What does the case and face plate look like. My 148 could use some cosmetic
surgery.

I have one of the chrome plastic face covers here that I THINK is
from a 148 (Just the chrome part no aluminum worded face plate)..I`ll
send it to you for free if you want it...It`s brand new but has been in
my desk drawer not in plastic so it`s picked up some very light
scratches..E-mail me and I can send you a photo of it so you can see if
it is indeed for a 148 (Seems to have more switch and light holes than
I recall a 148 having)

  #19   Report Post  
Old February 24th 06, 02:58 AM posted to rec.radio.cb
Scott in Baltimore
 
Posts: n/a
Default Cobra 25LTD Classic tune up

What does the case and face plate look like. My 148 could use some cosmetic
surgery.


I got your email. I've been busy. Will disassemble soon.
Wait for email with pictures. Phillipines unit, side mike.
  #20   Report Post  
Old February 24th 06, 04:21 PM posted to rec.radio.cb
james
 
Posts: n/a
Default Cobra 25LTD Classic tune up

On Fri, 24 Feb 2006 01:00:08 GMT, Lancer wrote:

+On Tue, 21 Feb 2006 21:04:25 GMT, james wrote:
+
+On Tue, 21 Feb 2006 04:24:38 -0800, Jay in the Mojave
wrote:
+
++james wrote:
++
++ On Sun, 19 Feb 2006 15:40:53 -0800, Jay in the Mojave
++ wrote:
++
++
+++Hello All:
+++
+++I am hearing that many guys are addeding in another modulation IC, and
+++Modulation transformer to double the audio power, allowing a higher
+++carrier power to be 100% modulated.
+++
+++Jay in the Mojave
++
++
++ ******
++ The carrier in Double Sideband Full Carrier Amplitude Modulation
++ should remain constant during modulation. If not, then you have a far
++ greater problem.
++
++ james
++
++Hello James:
++
++No thats not how AM works. The Modulation increases and decreses the
++amptitude during Modulation. Thats how double sidband full modulation
++works. Look in a old ARRL Book.
++
++
++Jay in the Mojave
+*****
+
+I think you need to go back and reread and comprehend what those old
+ARRL handbooks say. Then m aybe I suggest a good university textbook
+on Communications. Oh by the way you may want to brush up on y our
+Calculus and Differential Equations at the same time.
+
+Whats your damn problem james, does being a pompous ass come natural
+to you?
+

******

Really now. Maybe you should go back and comprehend what told me. I
just responded in a manner that reflected my education and skills. If
that is pompous to you then so be it. But mathematically to truely
understand AM modulation does require a higher level of mathematics
than just adding two plus two.

********
+
+AM(t) = f(t)*cos(wc*t) + A*cos(wc*t)
+
+where AM(t) is your Amplitude modulated signal with respect to time.
+f(t) is the function that mathematically describes the modulating
+frequency.
+wc is the carrier frequency
+t is time
+A is amplitude
+
+Taking the Fourier Transform of the carrier portion (A*cos(wc*t)
+yields an impulse function with amplitude A at frequency wc. The rest
+of the equation is your double sideband suppressed carrier and when
+the Fourier transform of this is taken it will yield a frequency that
+is the audio frequency plus and minus the carrier frequency at
+amplitude of half the audio power.
+
+I hope that this helps in your understanding of what Double Sideband
+Full Carrier Amplitude modulation, more commonly called AM, is.
+
+As long as you understand it, thats all that matters...
+

*****

Yes I very well do!

****
+
+james
+
+Does your formula show that SSB is AM also?

*******

Yes, remove the A*cos(wc*t) term and you have Double Sideband
suppressed carrier. Add a term for a bandpass filter and you will have
single sideband suppressed carrier.

Yes DSB and SSB are AM signals.


james
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