I was in an conversation with regard to a 902 MHz enthusiast list, and we were discussing issues that may be unique to the 902 MHz band due to the ARRL band plan, that was adapted to reflect reality in much of the USA with regard to easily adaptable commercial equipment.
The real life ham bands where the FM next to weak signal situation might occur (in the USA) based on the ARRL band plan include:
|50MHz||The SSB/CW only and “any mode” meet at 50.3 MHz. Do most FM operators stay about 51MHz?|
|144MHz||I assume most weak signal work is at least 100 kHz away from the popular 144.390MHz APRS frequency|
|220MHz||Again a case of ~100 kHz spacing between FM and whatever weak signal work may exist|
|440MHz||The satellite band with what are typically very directive antennas keep multi-MHz separation between FM and weak-signal|
|900MHz||I would expect below 902.080MHz and above 902.120 MHz to have heavy interference for weak signal operators according to the band plan.|
The situation I felt hinges on:
- what the relevant FCC specifications demand for “off-channel, in-band” emissions – is this just specified as say -60dB so many kHz from center channel, or with an emission mask. In either case, is the specification sufficient to protect a weak signal operator within N km of a powerful FM transmitter?
- If the specification is not sufficient for weak signal protection from nearby (in range) FM transmitters, do the practical filter implementations used by the most frequently used equipment provide enough protection any way as a corollary to meeting the FCC specification?