Ed, Loads of activity on the east coast on 40 meters on weekend mornings. 7285 to 7295, 8 am till about 2 pm when the broadcast stations come on. There are a wide range of people on 40, running all sorts of rigs. There is typically a lot more space and less interference on 40.
Looking at the scope, the only thing you can see is the peak modulation and if you close the carrier down. Voice waveforms are hard to look at on a scope. My scope is hooked up to the receiver IF, so I get both transmitted and receive modulation indications. Under modulation, you should double the carrier and almost close it down, giving about 200 to 300 watts pep at 100% modulation. The human voice is not symmetrical, so its not unusual to have 20 or 30% more modulation in one direction. You want the have the higher output in the positive direction. Light compression helps, most use modern compressors that reduce gain above a threshold, and don't go into it much, otherwise it sounds poor. To get good positive modulation, you need plenty of rf grid drive, good modulator tubes, and to have the audio phased correctly. One mod tube can be weak and limit peak modulation in one direction, positive or negative. For an antenna, the most wire you can get up is best. I cut a dipole for 40 and one for 80, resonant at the AM frequencies and don't use a tuner. The shorter the wire, the worse it works. Brett N2DTS > > Hi Guys; > > I am new to this list so please forgive me if my questions are dumb or > redundant. I just rebuilt a much abused Heathkit DX-100B. As > far as I can > tell it is operating OK into a dummy load. I have not put it > on the air > yet. For one thing, I don't have a 75 meter antenna up yet. I have a > mobile ant I will install as soon as I have time. I do have a > MFJ G5RV jr > that is good for 40 meters and higher. I have not heard any AM on > anything but 75 meters. Is there activity on 40 and / or 20 meters? > > I modified a scope to serve as a modulation monitor. I > noticed 2 things > that puzzle me. > > 1. It is hard to tell modulation percent with voice as the > waveform keeps > changing and unless I use a sine wave I can't sync it to get a good > envelope pattern. Any trick to this? > > 2. Using the mod mon I see that it is very easy to over-modulate. If I > keep the modulation down so I don't see short bright lines in > the center > of the screen (carrier disappearing, I think) , the average > modulation is > around 50% except for occasional peaks. Is this normal? would a > compression amplifier help? Thank you. > > 73, Ed Richards K6UUZ > > _______________________________________________ > AMRadio mailing list > [email protected] > http://mailman.qth.net/mailman/listinfo/amradio
