| Author |
Message |
    
Ssonnentag
New member
Username: Ssonnentag
Post Number: 2
Registered: 2-2005
| | Posted on Tuesday, February 22, 2005 - 12:51 pm: | 
|
The excerpts below were copied from the S-9 specifications. But they don't mean a whole lot to me. Could someone please explain in plain terms what this modulation, compression and swing stuff is all about? Thanks.
# TOP GUN? Modulator - A Magnum Exclusive!
- Turns the S-3's transmitter section into a modulator
- With 1 watt carrier - swing to 40+ watts!
- 100% modulation for unbelievable power
- Modulator On/Off Control on Front Panel
# TOP GUN? Compressor - A Magnum Exclusive!
- Compressor Improves Transmitted Audio
- Helps Punch Through Crowded Airwaves |
Mrbigshot
Junior Member
Username: Mrbigshot
Post Number: 18
Registered: 2-2005
| | Posted on Tuesday, February 22, 2005 - 3:41 pm: |
|
a modulator is a small linier ampliphier that uses 1 power transistor, in this case a 2290. a speech compressor takes your signal and filters and ampliphies it, but it makes it remain constant. for example a 2db signal will get amped intil its 20db and will be loud. if you yell it wont get anylouder than a wisper would.
the compressor is a nice feature but it isnt going to to anything more in the end than a good tech could do. the nice thing about the magnums now is that you dont need to have the peaked, they come that way. |
Therealporkchop
Intermediate Member
Username: Therealporkchop
Post Number: 161
Registered: 11-2002
| | Posted on Wednesday, February 23, 2005 - 12:52 am: |
|
So what you are saying is the S-9 has a 2290 transistor in it? |
Racer_x
Junior Member
Username: Racer_x
Post Number: 26
Registered: 2-2005
| | Posted on Wednesday, February 23, 2005 - 6:11 am: |
|
Modulation is the information added to the RF signal. Amplitude Modulation is made up of a carrier, a lower sideband, and an upper sideband. The carrier contains no information. When a carrier is modulated by audio it generates the upper and lower sideband which contain exactly the same information, they're just at different frequencies. The upper sideband is above the carrier in frequency, and the lower sideband is below the carrier in frequency. The sidebands are where your voice information is carried. This is why everyone who used AM has long since gone to using Single SideBand. It's far more efficient becuase one of the sidebands and the carrier are filtered out and the signal is pure modulation.
Compression is a type of speech processing where the dynamic range of the audio is compressed so the signal is more even in volume from the peaks to the valleys. The more compression the less natural voice sounds, but it's got a more even volume level. In general, having a speech compressor built into a CB is a good thing in that you'll sound louder on that radio than most. I don't know what Mrbigshot meant about a good tech doing more for you. Perhaps he was talking about having the limiter disabled to allow the radio to achieve higher levels of modulation than normal. Unfortunately that causes splatter because of overmodulation. Compression creates higher modulation without splatter.
I still don't quite understand the swing thing myself. Some folks think that AM power output should swing a great deal from a dead key to 100% modulation. In classic Amplitude modulation there isn't much swing. By definition an AM signal that is 100% modulated should show only 50% more average power output than the carrier alone. That isn't much swing. Some think you should see a 4:1 ratio of swing to the carrier, but they are mistaken. Classic AM at 100% modulation does show a 4:1 ratio of Peak Envelope Power to carrier power, but without an oscilloscope you cannot accurately measure PEP power. Very good PEP meters can get close, but they are meant to be used with a constant tone rather than speech.
Further, unprocessed speech has been measured by bell laboratories to have a 10:1 dynamic range, so with unprocessed speech you should only see about 10% average modulation. All CBs have some compression built into their audio circuit, so you can add another 10% - 20% for a maximum of about 30% average modulation. So if you only are getting about 30% average modulation, the average output of the radio should be only about 30% of the maximum of 50% more than carrier power. That means that the real swing you should see is only about 15% more average power than the carrier. Not very much swing at all. |
Racer_x
Junior Member
Username: Racer_x
Post Number: 28
Registered: 2-2005
| | Posted on Wednesday, February 23, 2005 - 9:14 pm: |
|
I forgot about modulators. Real modulators are generally a stage in a radio's transmitter section where the modulation is added to the carrier.
What CBers generally refer to as a modulator are small amplifiers. I don't know what class of amplifer they are, but I'd assume that they're class C as most CB amps are class C. Class C amps aren't linear and really shouldn't be used with AM or SSB as the output power changes with modulation in these modes. Class C is better suited to FM or CW where the power doesn't change with modulation.
These "modulators" don't do anything to increase the audio of a signal as they are RF amplifiers. There are some amateur radio RF amplifiers that do RF speech processing, but I've yet to see a CB amp that does RF processing. I suppose if they aren't used correctly they could cause a problem with RF envelope and change the audio, but I seriously doubt it would be for the better.
The "modulator" in the radios that you mentioned is a circuit that reduces the carrier of the AM signal until modulation is added, and then the carrier is increased in proportion to the amount of modulation. This makes the signal really swing. Why is beyond me, but some folks think it's better. I can't understand how because the average output power is actually reduced.
Some say it is better suited to run an amplifier. Again, I don't know how. If an amplifier can't handle a high carrier and then the added envelope of modulation in a linear fashion - as it should be for either AM or SSB - then having a reduced carrier that then increases with modulation to the same peak levels really can't be any better. Either way it seems to me that the amplifier is being driven beyond the point of linearity and that's where distortion and spurious emissions are more likely to happen. |
|
