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Audiophile73
Intermediate Member
Username: Audiophile73
Post Number: 125
Registered: 5-2004
| | Posted on Thursday, October 12, 2006 - 9:02 pm: | 
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O.K. I have been doing some reading, I know that a fully modulated signal on A.M is 4 times the carrier amount (1-4, 100-400). So why do all these export radios have so much forward power but remain clean. I talked to a guy who had a mirage that he said swung from 2 watts up to 16 and it was so clear. If the rule of thumb is correct shouldn't he only have a pep power of 8? |
Therealporkchop
Advanced Member
Username: Therealporkchop
Post Number: 908
Registered: 11-2002
| | Posted on Friday, October 13, 2006 - 4:03 am: |
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Because most likely he was getting his reading from a inaccurate meter, for starters. Some power meters that read PEP don't show 100% of the PEP scale, they may show only 75% or so. Just because a meter is a PEP meter or will read PEP at the flip of a switch, doesn't mean it's showing the full scale.
Most all of these radios will key really low (below 1 watt, but sounds like krap to me) and swing to an average of 30-35 watts PEP and some see 40 watts PEP. The RMS or average power reading will generally be 10-12 watts.
I've seen it on not a Bird meter or your average meter but on an actual service monitor..in the area of 25+ thousand dollars. No I don't have it, but the Tech's shop that I have started my "internship" in on Sat's does have it. And what I've said is right. But your talk power comes from average power and not PEP. PEP is important, but not so much as average power that the radio can hold on an "average".
PEP happens so fast, meters that can show PEP have to have an amp inside them to hold the meter. PEP without an amp inside the meter would either not move the needle period or it would bounce around like one of those super balls you use to get out of the bubble gum machine.
And yes you have to take harmonics into consideration also, so maybe (a big maybe) not all of that 40 watts PEP is true power. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1386
Registered: 6-2004
| | Posted on Friday, October 13, 2006 - 7:55 pm: |
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No meter - amplified movement or not, can accurately show a 4:1 PEP to carrier relationship because they are TOO SLOW. Perhaps if a constant tone is used, you can get close with a meter, but if voice is used you have absolutely no chance. That is why an oscilloscope is necessary to accurately check the modulation envelope.
Additionally, lots of folks now modify their radios so that the carrier power is reduced when no modulation is present. That's what's known as the "swing mod." I agree that the signal generally sounds bad this way. AM receivers depend on the carrier to demodulate audio. AM CB receivers don't have AGC set up to deal with a carrier that changes signal strength. There are all kinds of problems that can happen, and that's why good communication receivers have a way to change the AGC speed. Again, CB AM receivers do not. Result? Poor audio. |
Audiophile73
Intermediate Member
Username: Audiophile73
Post Number: 126
Registered: 5-2004
| | Posted on Friday, October 13, 2006 - 8:56 pm: |
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O.K well I have a Ranger 2950dx. I run that into a texas star modulator, then to a xforce 400hd. It is rated to give me 650 watts. So what should I set final carrier at? Right now when I key its at like 50 or so, then when I talk it will shoot to 450. What is that? How can I set this up to sound its best |
Therealporkchop
Advanced Member
Username: Therealporkchop
Post Number: 910
Registered: 11-2002
| | Posted on Saturday, October 14, 2006 - 12:19 am: |
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My only suggestion is to experiment with it. I've been told to set my dead key on my radio to make my amp key like 100 watts, but I don't follow that and don't like it. I like to see around 30-40 watts of key and then let it swing what it's gonna do.
Try it at different points and get radio checks from somebody that knows something about a radio, not that one that likes to repeat himself 40 times on one sentence.
Better yet, get someone who has a similar voice to yours (if you know somebody like that) and take a mobile out and listen to your radio yourself. |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1895
Registered: 1-2005
| | Posted on Saturday, October 14, 2006 - 2:21 pm: |
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Audiophile, Your problem might be driving the Texas Star modulator with the 2950. Correct me if wrong but the 2950 is a dual final rig with about 40 or 50 watts output? Best to run the modulator with no less than 20 watts and at 20 watts the MOD will put out full wattage. Now you could drive the 400HD with the radio alone and audio will be loud and clear, BUT being that its a custom it can taKE twice the drive for more output. Maybe you could look into the driver boxes from X force designed for their amps, like the X-80 driver. The Texas Star amp is a different breed than X Force that can't handle the input like the customs with their metal boards.
Try this...If you have a single final radio like a Grant hook it up to the V Mod and try the 400 HD out. Bet you will be suprised at how clean your audio will be.
Hope I can help. |
