543, well yeah, but how are we supposed to know what 150% is without a dead carrier for a baseline?
im just messin' with ya.
LC
im just messin' with ya.
LC
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Why do HF transceivers have such low level AM modulation?
- Thread starter SMILEX2692002
- Start date
I have a neat vintage Hallicrafters HT-37 that can run true AM or SSB and even DSB-SC (double sideband suppressed carrier). That last mode helps explain the notion of "more than 100%" AM modulation. When running AM with the HT-37 you can adjust the carrier injection anywhere from the equivalent of 100% AM, all the way down to zero injected carrier. Now that situation with zero injected carrier but with both sidebands present can be called "infinite % AM". Forget about 125% or 175% modulation, we're running 1,000,000 % modulation since there's no carrier present. One helpful way to view the structure of an AM signal is with phasors. A phasor is not what Capt Kirk used when battling that big lizard on planet X in one episode.. This type of phasor simply lets you show the phase relationship between the carrier and the lower and upper sidebands in an AM signal. The carrier phasor is drawn as a voltage vector or arrow pointing to the right. Then draw a vertical arrow pointing up from the same starting point but make its length one half the length of the carrier phasor. Call that the upper sideband phasor. It's only representing one modulation frequency to keep the diagram simple. Now draw a second phasor that's pointing down and also make its length half the length of the carrier phasor. That's the lower sideband phasor. Now comes the dynamic part of this. Leaving the carrier phasor as the reference phasor pointing to the right, imagine the upper and lower sideband phasors spinning around, one clockwise and the other counter-clockwise. If the modulation frequency is 1000 Hz then those two sideband phasors will be spinning in alternate directions at 1000 'rpm'. As the two sidebands rotate there will be a moment when they are both pointing to the left and since each one is half the value (length) of the carrier phasor, at that moment they will cancel out the carrier phasor. On a scope that moment corresponds to when the overall AM envelope gets reduced to zero voltage. On the other hand, when the two sideband phasors swing around and are both pointing to the right, in line with the carrier phasor, that will correspond to the voltage peak on a scope. At that moment the sum of the carrier and two sidebands will be double in voltage value as compared to the original carrier phasor. That corresponds to a doubling in voltage of the AM signal. A doubling of voltage corresponds to a 4 X increase in power, as compared to the carrier by itself. That's another way to understand why the PEP level of an AM signal is 4 X the unmodulated carrier level.
I find that if you can run you rig with the carrier deliberately partially suppressed, say a Galaxy with the RF Pout dialed back deliberately but with the mic gain cranked way up, the Galaxy and any subsequent 'assistance' will swing higher because you're not burdening the amplifying devices with carrier power, especially if they are hindered by ALC action. To take this to the extreme, just run SSB, but now the other guy needs a product detector or other means to demodulate your signal.
Again what is the AM everyone is talking about?...
The AM rally starts this weekend.
SSB is kind of like Windows. AM is more like Linux.
That does make more sense. You had to know stuff back in the MSDOS days. Fortunately Windows came along for people like me.
You would be surprised how many times these day I have to go back to dos to get things done