Air Traffic from American Flight 1316 on VHF FM

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Hi KE5NGM! Your post was very interesting! Here's what I think about the cause of QRN by AA 1316on 146.58 MHz... According to your recorded display, it “appears” as if the interference (QRN) is off-freq from the carrier (146.580 MHz). Also, the receive S-meter level of +40dB suggests that the aircrafts’ location was very close to your station. Such an interfering signal could be caused by high TX power, or even the locality of the TX station and RX station. However, I believe the QRN to originate from harmonics and suitable atmospheric conditions. I've experienced this while in the military and as a radio and radar tech in the FAA, and even through the work that I've done as an engineer for the FAA. Civilian aircraft Air-to-Ground / Ground-to-Air radio stations (and FAA ground-to-air radio comm stations) transmit at relatively low power (at 25 W) and operate in the VHF range of 118.000-136.975 MHz. So, it is feasible to have a multiple frequency (harmonic) somewhere in the range of airborne comm frequencies, be received by 146.58 MHz. I’d rule out the aircraft having an output power greater than 25W. Since the RX signal was VHF and not HF, there would be no reason to transmit at a greater power than 25W. Also, the AA aircraft was at a high altitude, making its antenna higher than all ground-based Ham antennas and its transmission (propagation) was much better than all terrestrial stations'. Since your station is in Fort Worth, it is my guess that the aircraft was very close to your shack. It would be interesting to see if other Hams also recorded the QRN and then make a comparison of other their S-meter signal strength and received signal frequency spread on their display. My point here is at the time that you recorded the incident (at 20:24), what would a Ham closer to Austin see on their radio, compared to what you recorded. From the recording it is clear that other Hams in the net heard the QRN, but the question is, how strong a signal did they receive the QRN at that exact time? I'd bet that their S-meter would be different, but the signal spread would be close to what you recorded. That would prove that the QRN was due to harmonics and not that aircraft having high power. Also, if you take a look at the carrier on the recorded display, AA1316's frequency spread is off-set from the carrier (146.58 MHz) and is not as "tight" or concentrated (it is spread more across the band), as compared to other stations. Also, since the North Central Texas Simplex nets' frequency is at 146.58 MHz and aircraft radio frequencies are not in the Amateur Radio Frequency band of frequencies, it is safe to rule out that the pilot was not intentionally operating on an amateur frequency. Not really related to this QRN, but interesting just the same, while I was in the military (many years ago, in the 1980's), half of my Army unit was in Arizona and the other half was enroute to Florida. I was in the mountains of Arizona, on watch using a VHF radio and could clearly receive our other units in Florida on the same VHF frequency. That QRN was due to skip or tropo ducting and not harmonics. I know this because both units were using the same freqs. Interestingly, the VHF transmitters used in the Army was also at 25W. According to the website, flightaware (search for AAL1316 or go to flightaware.com/live/flight/AAL1316), AA1316 left AUS at 20:03 CDT and arrived at DFW at 20:42 CDT. According to Flight Aware’s flight track of AA1316, at around 20:24, the aircraft was possibly beginning its decent to DFW. AA1316’s highest altitude was at around 23000 feet. AA1316 began its decent near Granbury, TX and by the time it was near Fort Worth, its altitude was 12100 ft. This would explain your strong S-meter reading. But the frequency spread could only be caused by the "physics" of RF. In other words, harmonic frequencies, or in Ham lingo, QRN. So, it’s my opinion that the most likely cause of the QRN, to the North Central Texas Simplex was caused by harmonics from the AA airborne transceiver. By “chance” the North Central Texas Simplex net (and your station) experienced what the FAA would call “an anomaly” due to harmonic interference, thermal properties of the atmosphere and/or the relative location of the aircraft to the receive stations. It as simply an anomaly. But I think it was a very cool anomaly just the same! You never know what radio will throw at you! That's what makes amateur radio so interesting! 73’s!