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Old 06-02-2011, 12:41 PM
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Default Can a radio's RF REALLY be turned up

I have a few people who like to play with the power output on CB radios. It was explained to me by 1 of them that, if you turn the carrier up, you have to turn the madulation down and if you turn the modulation up, you have to turn the carrier down. If this is the case (and it must be because I sizzled a radio once by turning everything up!) does a CB really give more output power, or are you just swaping 1 for the other? Is there REALLY a way to turn RF power up without having to put in bigger finals and what not else? (In other words major surgery)
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Old 06-02-2011, 1:12 PM
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Theres not much you can gain so its not worth it. I dont see any sense in turning a carrier up and lowering the modulation or vice versa. If the radio cant handle both then its time to get an amp.
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Old 06-02-2011, 2:24 PM
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Well, that was 1 of the things someone told me is that, if you have an amplifier hooked up, you have to turn the power down so you don't over drive or sizzle the radio and/or amplifier........true, or no?
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Old 06-02-2011, 2:31 PM
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Wirelessly posted (BlackBerry9630/4.7.1.57 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/109)

With in the limits of the transistors, but unless you double the power output you not going to gain anything, other than more heat, and once you exceed the limits of the PA you will let the magical smoke out...
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Old 06-02-2011, 2:36 PM
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That's exactly what happened to me once. (Lucky it was a $20 Uniden and not my Cobra-148!) I guess what I'm wondering is, is there a way to torment more people out there without buying an amplifier (which I don't know where to get anyway -unless you buy an amateur 10-meter amplifier and know what you're doing enough to make it an 11-meter)
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Old 06-02-2011, 5:20 PM
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Most amps are designed to be driven by a stock radio so leaving it alone is best. About the only thing that can help you is the super modulation mod that there is for the newer radios. It will suppress your carrier so you CAN peak the radio out safely. But I have done the mod and its kinda difficult to adjust. You need to be monitoring your signal and NOT suppressing the carrier too much. The mod is far from ideal but works.
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Old 06-02-2011, 5:43 PM
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The basic criteria for modulating a conventional AM transmitter is whatever the RF output power is you need 50% of that in audio to reach 100% modulation.

So, a 4watt CB transmitter would need a clean 2 watts of audio to reach 100% modulation. If you can turn up the carrier to say 10 watts and the audio modulator can only produce 3 watts of clean audio the transmitter will not fully modulate and you will push the audio modulator into distortion.

The resulting distortion will cause excessive transmitter bandwidth and will probably not sound very good.
prcguy
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Old 06-02-2011, 9:47 PM
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Quote:
Originally Posted by prcguy View Post
The basic criteria for modulating a conventional AM transmitter is whatever the RF output power is you need 50% of that in audio to reach 100% modulation.

So, a 4watt CB transmitter would need a clean 2 watts of audio to reach 100% modulation. If you can turn up the carrier to say 10 watts and the audio modulator can only produce 3 watts of clean audio the transmitter will not fully modulate and you will push the audio modulator into distortion.

The resulting distortion will cause excessive transmitter bandwidth and will probably not sound very good.
prcguy
I'm not sure exactly what you're trying to say here, but a properly modulated AM signal reaches a peak envelope of 4x the carrier.
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Old 06-03-2011, 4:05 AM
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He is trying to say generally for a plate or collector modulated AM signal one needs at least half the audio output power as ones(I believe DC input is what we need. Not output.) carrier power to fully modulate the carrier.

I agree.

However.. Considering a stock CB radio is set at 5 watts DC input that will require 2.5 watts audio. Since a Cobra 29 is rated at 5 watts audio output power there seems to be enough audio to modulate 10 watts of average DC input power. Wich would be an 8 watt carrier.

Peaking a radio out usually gets a 6 watt carrier at most. So audio power isnt really the problem. The problems start when the transistor is already running warm because it has to handle the increased carrier dc carrier input dissapation PLUS the extra audio power you are pumping to it to fully modulate the increased carrier.
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Old 06-03-2011, 7:32 AM
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I'm trying to figure out exactly what is being said in the last few notes. (Sorry, but I'm the kind who's lucky they don't blow a radio up turning it on.) What I did once was watch someone take the wax seals out of 2 cylinder shaped objects (I think those are called "finals", but why they always have wax in them I don't know). I seen him hook up an RF/poer meter to the radio, and turn on them so I was getting.....what was it....like 6 watts output (or so as I understand). I figured "I want to see if I can get more", so I did exactly what I (thought?) I seen him do. Well, for a few days I was getting about 9 or 10 watts out of it (having fun tormenting people in the meantime) according to my power/SWR meter, but suddenly in the middle of a transmission the needle on the meter fell like a stone to about 1/2 watt. The guy who originally turned it up for me was like; "DON'T TOUCH THOSE! YOU JUST BLEW YOUR FINALS OUT!" I'm like; "Huh? NOW what'id I do?" To this day I'm still not really sure what he meant what I did. (I don't know where he is right now so I can't ask him.) It was a Uniden 510 or 520, if that helps. Is there ANY way to get say, 9 or 10+ watts out of ANY C.B. radio without changing half the circuitry? If not, how would I weld new pieces in it to MAKE it be capable of handling that amount of power? What kind of diodes or whatever would I need?
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Old 06-03-2011, 7:52 AM
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stevedogan .......... please leave the covers on your radio =)
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Old 06-03-2011, 8:26 AM
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Very basically, you can't really 'tune' more power out of a typical radio by just making a few adjustments. The average manufacturer isn't going to give away much for free. They design around a set of requirements and leave it at that. A watt or two increase isn't uncommon but it's useless as far as how well/far people will hear you.
Any useful increase in power means you will be making some major modifications, there's no way around that. If more power is wanted, then the easiest solution is to add an amplifier. The usual story about getting a large amount of power from a stock radio just by making a few adjustments is just 'hype'.
That advice abut leaving the covers on the radio is probably the best you've gotten in this thread!
- 'Doc
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Old 06-03-2011, 8:53 AM
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Quote:
Originally Posted by stevedogan View Post
That's exactly what happened to me once. (Lucky it was a $20 Uniden and not my Cobra-148!) I guess what I'm wondering is, is there a way to torment more people out there without buying an amplifier (which I don't know where to get anyway -unless you buy an amateur 10-meter amplifier and know what you're doing enough to make it an 11-meter)
I would not get an amplifier.

Legal reasons aside, for the gain you might get, you'd be better served with a better antenna system. Going from 4W to 100W is barely an S-unit. 100W to 500W is another S-Unit (Thereabouts, I'm not breaking out a calculator right now).

You can obtain the same gains by merely getting a better antenna. For mobile, it's hard to beat a 108" whip, hard mounted, using decent coax. For base, you have plenty of antenna options, and a 1/4 wave vertical, 1/2 wavelength above ground, with great coax is hard to beat as well.

All of these options costs less than the amp.

Also, you'll never find a good 10 meter only amplifier. The ones that claim they are 10M are really just crappy amps, that splatter all over the band.

Take my advice: Skip the amp, get a better antenna
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Old 06-03-2011, 9:13 AM
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Quote:
Originally Posted by UberGeek View Post
Legal reasons aside, for the gain you might get, you'd be better served with a better antenna system. Going from 4W to 100W is barely an S-unit. 100W to 500W is another S-Unit (Thereabouts, I'm not breaking out a calculator right now).
The difference of 4 watts vs. 100 watts is actually close to 2.5 S-Units, and then another to 500 watts for a total of 3.5 S-Units or 21db.

I'm not sure of any mobile antenna worthy of a 21db gain.
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Old 06-03-2011, 9:48 AM
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Originally Posted by Ohio_359 View Post
stevedogan .......... please leave the covers on your radio =)
You're actually not the first one that's told me that.
I'm not sure if anyone over your way seen the mushroom shaped cloud after I got done playing with the inside of that radio..... *giggle* Cute though. I'm STILL giggling away at that comment.
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Old 06-03-2011, 10:19 AM
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Quote:
Originally Posted by Ohio_359 View Post
The difference of 4 watts vs. 100 watts is actually close to 2.5 S-Units, and then another to 500 watts for a total of 3.5 S-Units or 21db.

I'm not sure of any mobile antenna worthy of a 21db gain.
Either way. 2.5 S-units difference is barely enough to make a difference on the person's end. you're going from 36 dBm to 50 dBm. It's barely noticeable.

But let's look at what I'm trying to say: For all the work entailed in putting an amp into a vehicle (Which often will need an alternator upgrade if it's a smaller vehicle), plus heavier guage wiring needed to support the power; when one can just put a more efficient antenna, and better coax.

And, one can gain 21db of signal, merely by getting better coax,.

And, one can usually get better returns by simply improving their ground plane.

Not to mention, the 4W to 100W really isn't even accurate. CB radios have a legal limit of 4W carrier. On a 100W amp, you'll only be getting a 25W carrier. If you're using SSB, you have 12W PEP, compared to 100W PEP. Now, you're only looking at 40 dBm getting bumped up to 50dBm. That's barely an S-unit and a half.

Now, 100W PEP to 1000W PEP is only another 10 dBm. Again, barely an S Unit and a half!

An amplifier would be the last thing I would look at getting to improve a station. Antenna, antenna, antenna. After you have the best gorram antenna you can get, then it's: Coax, coax, coax.

After you have the best coax, and the best antenna, then you look at consider an amp. The amp does no good if it's only cooking worms, or cooking your lossy coax.
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Old 06-03-2011, 11:30 AM
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Quote:
Originally Posted by Ohio_359 View Post
I'm not sure exactly what you're trying to say here, but a properly modulated AM signal reaches a peak envelope of 4x the carrier.
Not quite. A SSB transmitter would reach 4X the PEP of carrier if it was running in AM mode.

prcguy is correct in how he describes high level AM. It requires an audio power of 50% of the carrier power. That power is divided between two sidebands, so each sideband of an AM signal has 1/4 of the power that the carrier has.
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Old 06-03-2011, 11:42 AM
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Quote:
Originally Posted by UberGeek View Post
...Going from 4W to 100W is barely an S-unit. 100W to 500W is another S-Unit (Thereabouts, I'm not breaking out a calculator right now).
An S unit is an imprecise unit of measure, but the closest thing to a written standard says it's 6db. 4 watts to 100 is just shy of 14 db, and 100 to 500 watts is 7 db. 4 watts to 500 watts is 21db.

S units or not, 21 db is the the difference of a quarter microvolt to 2.5 microvolts in a receiver - a substantial increase.

Quote:
Originally Posted by UberGeek View Post
You can obtain the same gains by merely getting a better antenna. For mobile, it's hard to beat a 108" whip, hard mounted, using decent coax. For base, you have plenty of antenna options, and a 1/4 wave vertical, 1/2 wavelength above ground, with great coax is hard to beat as well.
You're describing a unity gain antenna, so 4 watts would be 4 watts ERP, assuming zero losses between the transmitter and the antenna. a 21 db gain antenna at 27 MHz would be HUGE, and it's not likely that too many of us have sufficient real estate to contain one.

Quote:
Originally Posted by UberGeek View Post
Also, you'll never find a good 10 meter only amplifier. The ones that claim they are 10M are really just crappy amps, that splatter all over the band.

Take my advice: Skip the amp, get a better antenna
We're in agreement here.

Quote:
Originally Posted by UberGeek View Post
Either way. 2.5 S-units difference is barely enough to make a difference on the person's end. you're going from 36 dBm to 50 dBm. It's barely noticeable.
That's going from a quarter microvolt to a bit over 1 microvolt, and can mean the difference between communicating and not communicating. I'd say that's pretty significant.


Quote:
Originally Posted by UberGeek View Post
And, one can gain 21db of signal, merely by getting better coax
Really? REALLY!? One can only gain 21 db of improvement with better coax if the coax one is using to start with has over 21 db of loss.
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Last edited by zz0468; 06-03-2011 at 11:49 AM..
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Old 06-03-2011, 11:57 AM
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Originally Posted by zz0468 View Post
Not quite. A SSB transmitter would reach 4X the PEP of carrier if it was running in AM mode.

prcguy is correct in how he describes high level AM. It requires an audio power of 50% of the carrier power. That power is divided between two sidebands, so each sideband of an AM signal has 1/4 of the power that the carrier has.
It sounds like you are comparing the view on a scope and the readings on a watt meter. On a scope you'd see the carrier double and on a watt meter you'd see the carrier quadruple at 100% modulation.
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Old 06-03-2011, 12:12 PM
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Quote:
Originally Posted by UberGeek View Post
And, one can gain 21db of signal, merely by getting better coax,.
21db is pretty huge considering that it only takes 3db or less for the audio to be discernibly louder at the RX station. So even your example of a 4 watt carrier vs. a 25 watt carrier is equal to an 8db increase in audio and is a substantial increase. So also considering that 1/2 S-Unit is noticeably louder to the ear, I'd say that a 3.5 S-Unit is a very noteworthy gain.

I will agree with you on one thing though, I'd rather put 4 watts into a good coax and antenna setup, than 100 watts into a coat hanger, but considering that good coax will only lose ~.5db per 100' run, there is no possible way to ever realize a 21db gain from coax, especially in a short mobile run.
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