carrier or modulation

[9deuce]

:::CARRIER OR MODULATION:::

:redface:

this is a heated debate around my way i figured id ask you guys since you've been in the cb game longer then me...... ive been doing cb for 8 years now and all i hear i need to have a low deadkey and 100% modulation...... then i hear from others a higher deadkey with with 50% modulation..... im just wondering witch is beter or should i say what would be good for DX..... i just ordered a connex 3300fhp i have a tech who will do tuning free of charge since i mow his lawn and give him a good price ....SO.. need to know what i should ask him to do to it.... i know im gonna run a 4 pill in the future so low seting will be setup for 2w deadkey and 25w pep..... so on the high setting im just wondering what should i set this at max deadkey with 60% modulation or a 5w deadkey with 100% modulation...... can some one shed some light on this im confused since the guys i talk to around here have diffrent setups but sound the same maybe ones a S-unit higher but the other swings to about the same level....and others have so much modulation its distorted and sounds like a speaker on high vol and its fuzzy sounding....so those the guys get into a pissing match telling those guys what to do... **LOL** sometimes this goes on for hours at a time and i sit back and listen hoping to gain some insight with my bearcat980 laughing not getting no real info so i guess this is a lower higher debate and trying to figure out what to do plz help thnx

have a great day and god bless

 

[9C1Driver]

Never heard of making a radio do a high dead key at 50% modulation. Never seen that in a factory tune up manual either. Must just be a local great debate in your area.

 

[RatsoW8]

I do believe that a perfect 100% modulated carrier is the standard for AM regardless of the power level.

If your guy is actually a radio technician he will know how to set your modulation to 100% and he'll be using a scope to do it.

 

[Captain Kilowatt]

Whatever the power output setting is always go for 100% modulation. The only time I ever heard about running less than 100% modulation was back in the heyday of international shortwave broadcasting. A lot of the really BIG tube transmitters (250 Kw or more) ran about 85% modulation. This was done purely for economic reasons and was a decent trade-off between 100% modulation and tube life. The modulator tubes would last much longer at that level. Those transmitters typically ran a pair of tubes in the final RF stage and another pair in the modulator stage. Class B modulation service is much harder on tubes than class C plate modulated RF service is and when you have 250 Kw or even 500 Kw in some cases if you can't be heard at 85% modulation you have other factors involved than simply adding a little more audio.

 

[9deuce]

thnx fellaz ill be taking it to my buddie and letting him do his magic

 

[KM3F]

What you was told in your first post by the CB hotshots.. neither one is correct.
Since you came here to ask, take our advice over what you hear.
If your tuner does not agree do let him do anything but make sure modulation is 'near' 100% not over, for whatever power level you decide on
Here is how it works regardless of carrier (dead key) level.
Simply stated, the dead key level times 4 is the max. 100 percentage of modulation you should never exceed to stay clean for audio.
Example is 2 watts x 4 = 8 watts peak envelope power not 15, 20 or any other power.
If your going to drive an amplifier, this peak has to be at or below the amplifier's input/output rating to stay clean.
Please listen and not fall into the stream with the rest and become deaf to the correct way things work.
Good luck.

 

[9deuce]

hehe

thnx

 

[unit248]

KM3F is right on the money.

This can get a little messy once you factor in an amplifier though. The problem is that you need to determine your amplifier's peak output power level and then divide that by 4 in order to decide how much AM carrier power to use. What makes that hard is that most stated output power ratings for CB amplifiers are gross exaggerations. Your DaveMade two-pill probably isn't going to do 500 watts no matter how many fancy decals you put on it.

Also, even if you can achieve the documented PEP rating for the amp, you probably ought to back it down a bit anyway, because more often than not they design the amps so that the transistors are operated well outside its linear region. Basically, the amp should provide a fixed multiplication of power: 1 watt in gives 2 watts out, 2 watts in gives 4 watts out, 3 watts in gives 6 watts out, and so on. That's what they call a linear progression. But that doesn't last forever: by there time you get to 10 watts in, you may only get 18 watts out, and when you get to 11 watts in you may get only 19 watts out. Basically, the input to output ratio starts to degrade the more you push the transistor towards its maximum rating. Once you get to that point, the output waveform will be distorted, and the distortion contributes to bleed over and possibly crummy audio. You'll also tend to make the transistor run hotter than it was designed for, which will make it more prone to failure.

If your goal is to just "drop the maul" on someone at a shootout, then maybe squeezing every last watt out of your transistors makes sense. And that's fine. But if you want to keep your output signal clean and you want your equipment to last, you probably ought to back off the drive to the amp a bit and run it a little under the stated rating.

Now, if someone's just plunked down money on a kilowatt amplifier, they probably won't want to be told that they should keep the carrier power set to 250 watts. I mean, that's crazy talk, right? You want that full kay dubya! Well, with a properly modulated 250 watt AM carrier, you will hit 1KW on a voice peak. If you crank the carrier higher than that, you'll just create splatter and give yourself that crispy, crunchy sound.

What you really need to do is:

1) Determine your amp's peak output rating. You might be able to do this with a wattmeter by adjusting your radio's dead key slowly upwards until the amp's output power can't go any higher. Don't keep it keyed up at max output for too long. Make a note of that power level.
2) If this is a CB amp, you probably want to subtract about 10 percent of that result just to keep the amp cool. If you measured 1000 watts, then reduce that number to 900 watts.
3) Take the result from step 2 and divide by 4. That should be your carrier power. If as above you calculated 900 watts, then result would be 225 watts.
4) Re-adjust the radio's dead key output until the amplifier output equals the value you calculated in step 3 (e.g. 225 watts).

I know some people with fairly big multi-stage installations where there's a driver amp between the radio and the big amp. That makes it even harder to calibrate everything: the same rules still apply, but you may need to repeat all the steps a couple of times to balance everything out. Ideally, you would have an oscilloscope so you can monitor your output signal. This will show you if your positive peaks are "flat-topping," which would indicate that you're driving the amp past its maximum output.

Now, you can have more than 100% positive modulation, but doing this without creating even more distortion is harder than it sounds. When someone says "I've got my dead key set at 2 watts, but I swing to 50!" then they've probably got the modulation limiter in their radio disabled, but they're probably also generating a lot of distortion products. You can only tell for sure with a scope (and a spectrum analyzer). I think 150% is probably as far as you want to go. In any case, you still need to factor that into your decision of where to set your carrier level relative to your PEP figure (with the example above, it would probably be more like 200 watts).

-Bill

 

[Z-MAN 369]

The Connex you got is a duel final radio that should do around 50w pep. Have him set the low carrier at 2w, high at 10w and adjust the mic gain for whatever % modulation you need. Dont cut the limiter but have the VR turned up for max pep.

 

[KM3F]

Bill, ever get the feeling this falls on deaf ears?
All the die hard CBers want to do is see meter needles fly, believe, and stuff the screw driver mechanics pockets with money..
To heck with proper equipment operation.
Just drive the h*ll out of it until it burns then wonder why..
Good luck.

 

[GnG8d]

All the die hard CBers want to do is see meter needles fly, believe, and stuff the screw driver mechanics pockets with money..
To heck with proper equipment operation.
Just drive the h*ll out of it until it burns then wonder why..

My you paint with awfully broad strokes :bdh:

 

[boomer111]

So here is how I do it.

4 2sc2879 pills being driven by a Stryker 440 HP radio.

I know the rat shack meter reads about 500 watts so I adjust the power on the radio till the meter reads close to 125 watts dk. with the amp in line.

Then I take the amp off line and check the dk power output of the radio alone and multiply it by 4 then I set the mic gain so it shows roughly four times the radio dk when talking.

Verify with on the air reports.

This should get you in the ballpark.

Without a scope and an spectrum analizer this is close enough.

Oh ya and make sure your standing wave ratio is as low as you can get it. This too can be reason for debate.

 

[W5LZ]

Actually, those 'broad strokes' aren't quite broad enough, double them and it's almost approaching adequate.

Amplifiers have nothing to do with modulation percentage, the transmitter does that part. The amplifier only 'amplifies' what it's fed. The output of a properly fed amplifier should have the same 'mixture' of carrier and applied modulation to equal the percentage fed into it. That simple, really...
- 'Doc

 

[GnG8d]

Actually, those 'broad strokes' aren't quite broad enough, double them and it's almost approaching adequate.
- 'Doc

Do you hang out on 27.025 by accident on that modded HF rig do you?

I do have to pay attention to how I use that radio to keep from transmitting where I shouldn't, and that can be a problem.