17-03-2018, 01:22 PM
(17-03-2018, 08:59 AM)VK4AQJ Wrote: <snip>
The other concern is that even though the second harmonic from the broadcaster is reported as 50dB down, that may not be enough, and no amount of filtering at 927kHz will address a second harmonic at 1854kHz.
- Jim
That may end up being your problem.
Some years back I worked at Mildura airport, and 3MA one of the local AM stations was on 1467kHz. Aviation changed from HF AM to SSB, and at the same time the frequencies used changed.
Our 2MHz frequency became 2944kHz, and the second harmonic of 3MA being 2934kHz caused interference from day one. I recall a report was filed with the then P&T Dept. and correspondence went back and forth with a reminder about interference to air navigation etc.
The 3MA site was about 10km from our airport HF receiver site, and I think it was determined at the time that the station could legitimately radiate something like 5 Watts second harmonic and still be in compliance with the regs. That 5 Watts was enough to cause the problem.
The final outcome was that naturally no way was 3MA going to change their frequency, and so the aviation network changed the 2MHz frequency from 2944kHz to 2869kHz and all was then OK.