Total posts : 45366
Probably…that is if the level of the 3rd is high enough to be detected. A filtered transmitter will always have a little left over as the harmonic count increases..and decreases. You will probably find the same result going the other direction..below the MW band with the same level of harmonic signals as the positive side.
Both will gradually decrease in signal level..going up or down. 1620 is a good ways from 540, but if the receiver is highly sensitive, would pick it up and sound like a strong signal. A spectrum analyzer would be needed to see it’s level and verify the regular radio is actually picking up a harmonic rather than a ghost signal.
I’ve seen situations where a harmonic, 2nd or 3rd is notched down to as low as -60db and measure as such on a spectrum analyzer. Then taking a regular radio with sensitivity would make that 3rd sound as strong as the 2nd and fundamental carrier!
The TH units are good units IMO. But they are not built with precision in mind. They are intended to sell houses via a voice message, external or recorded internally. They were not designed for “broadcasting” in the sense of broadcasting programs or music. If they were designed for that purpose, far better specs and tolerances would have been incorporated into them.
But they are what they are and can work really well.
Noting back on the scope displays of the modulated signal, the waveform is incredibly “lop-sided” to the positive swing and quite crunched to the negative side of the waveform. That should be nice and symmetrical, both positive swing and negative swing..leading to my theory that the problem with that unit is in the modulator circuit and having a strange DC offset taking place when modulation is applied. The DC level should remain constant and only the AC component of the audio signal changing the voltage and current applied to those finals.
I suspect the modulator op amp IC to be flaky. If it was driven hard prior, that could have damaged the op amp IC’s internal characteristics with respect to maintaining a steady DC offset voltage on it’s output, thus operating the two finals way out of designed spec, affecting the range seriously..as well as showing up on a scope incorrectly..though the scope should not be ruled out as it could be adding to the actual problem in it’s displaying of what actually is coming out of the transmitter.
Adding, actually the third harmonic would be at 2160, a multiple by 2 from the 2nd at 1080. Also the glass itself, which is comprised mostly of sand particles, will also affect a low level signal, even more so if said glass is made to change it’s shade during the day, or has UV wavelength reflecting material embedded into it. But I don’t think that is what is causing the unit’s degraded performance. More likely an internal problem along that modulator circuit IMO.