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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 |
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. |
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. |
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? ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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 |
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. |
Cobra 25LTD Classic tune up
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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) |
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. |
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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