"The drop in current has to do with what I was describing. The carrier will actually drop when audio is appied instead of the inteligence being added to the carrier. As mentioned, duty cycle comes into play here also. The amp draw drop is "normal" As for your radio meter, I dont know what to tell you there other then alighnment."
Change a couple of words in that and you'd be closer to being right about what happens. As it stands it isn't correct.
The carrier's power level should not change at all, it stays constant. If it does, something isn't right. That's with the current/voltage applied at the input to the carrier 'generator' (Oscillator).
The output power of the modulation stage changes with the audio applied to that stage. No input audio, no output power from the modulation stage (circuit). Audio is not constant, it fluctuates with the frequency of the audio applied.
When you combine these two signals you produce an amplitude modulated signal, which when not over driven by the modulation will produce a signal who's power level fluctuates between the sum of the powers of both signals to zero power level at 100 percent modulation.
The power supplied to the two stages will only be as low as the max power of the carrier. That's the power drawn from the power supply/battery. The power when measured at the output of the transmitter will be a max of the sum of the two stages, carrier and modulator. That's normal, to be expected. That input power is never the total drawn from the power supply, there are the circuits themselves which consume power, along with any other circuits of the transmitter. You can't use the measured input power to the transmitter as an indication of output power with out accounting for efficiency. Power in will always be more than power out. Nothing is 100% efficient.
The other 'end' of it, what you see on an 'S' meter.
The minimum reading on that 'S' meter is band noise with no received signal. That level may or may not be constant, but figure on it being constant at whatever level you see indicated with no signal present. When a signal is received, that 'S' meter will read higher and gives you an indication of how 'strong' that signal is (the reason for having an 'S' meter to start with). If that 'S' meter is accurately calibrated it can give you a fairly accurate estimate of the strength/power output level of that signal is you know what the 'other' factors in that calculation are (distance between you and that station, ERP of both antennas, and more). That calculation can certainly get close, but is never entirely accurate (one of those "at least this much" guesses). Knowing enough to do that calculating almost never happens, aside from the fact that 'S' meters are almost never calibrated accurately. So, what you have is ONLY an indication of a received signal's strength above band noise, and no two stations are ever the same. All of which is sort of beside the subject of 'reverse swing', but you should know so you can understand what you're seeing.
If a signal has 'reverse swing' it is an indication of less power output on modulation being applied to that carrier (on
AM, no such thing as 'reverse swing' without that carrier). Which means that the modulation and carrier powers are 'canceling' each other. Which means that the applied modulation's power level is higher than the carrier's power level, which produces a 'negative' power which only means it's sucking power out of the ether instead of putting power into it. Which! If you know anything at all about this stuff is impossible. (But a neat thought though, ain't it?) What's actually happening is that there is a time period (microseconds) when no power is being transmitted. That causes the 'S' meter needle to drop back or 'swing in reverse'.
All this is the long way around of getting to the fact that 'reverse swing' is an indication of over modulation, which results in less or no transmitted power. The root problem is the over modulation part. All the rest of this is just leading you by the hand through the whole process so you can see what/why it's happening.
ALC has to be adjusted properly for that ALC meter to tell you anything. It sounds like it isn't adjusted properly. Why? I have no idea. If you get the knowledge, understand it, and remember it, you don't have to put up with all this crap of someone telling you. It's your own fault.
- 'Doc
Some times it's easier to understand if you think of it in terms of CW and
SSB combined which yields
AM mode. (How'z that for complicating things??)
Linear Mode
