Total posts : 45366
In my previous post I mentioned antenna Q in response to a statement that the high Q antenna increases splatter. It does just the opposite since it acts as a narrow band pass filter. You are correct that the splatter will not be eliminated this way but I point out that if antenna Q is a factor, splatter will be reduced rather than increased. Because it is hard to control the Q and tuning of a coil loaded short antenna, this is not the approach to use to reduce splatter which needs to be prevented at the transmitter. A high Q antenna will supress the wanted sidebands and make the audio sound poor. I use a coil loaded resonant antenna and had this problem so I “spoiled” the Q with a shunt resistor.
It is true, as you said, that a receiver may not hear the splatter while tuned to the signal. I maintained a college carrier current AM system and would check for splatter by tuning the receiver off the signal. With experience, I could determine by listening off frequency if the transmitter was overmodulated on the negative peaks.
Spurious signals such as splatter are caused by improper transmitter adjustment (or perhaps poor design) as you discussed, and it is very important not to overmodulate and secondarily to limit the audio bandwidth. The NRSC preemphasis curve boosts the higher audio frequencies which with a deemphasised receiver gives a better signal to noise ratio. This curve also limits the AM audio bandwidth to 10 kHz. thereby limiting the AM transmitted bandwidth to 20 kHz.
A spectrum analyser is a great tool for monitoring the transmissions, but an oscilloscope display of the modulated carrier observed by a “trained” eye is a low cost practical monitoring means which should be affordable by most hobbyists. They are available in the $50 range, though a can of contact cleaner may be needed for the scratchy controls.
I agree that one wants to provide a high quality audio signal that listeners will enjoy and I have nothing to add to that other than it begins with a properly operated transmitter.