Post #3751620

@trashpanda@m.alittlenook.net The concept you’re looking for is link budget: where all the energy goes between the transmitter and the receiver You have losses in your feedlines (connections to antennas) and even energy reflected back into your transmitter (measured by SWR) You have gain in the transmitting and receiving antennas You have attenuation from objects between antennas, and even in the general vicinity (fresnel zone) And then there’s free space path loss, the skin of rhe balloon, the inverse square law. (If you double the distance, the signal strength is one quarter, a reduction of 6dB which is roughly one unit on the S-meter (some restricitions apply)) Free space path loss is also proportional to frequency, because E = hf The crazy part is, because electromagnetic radiation is a reversible physical process, the gains and losses add up the same (in decibels) in either direction The minimum practical power to transmit is limited to the receiver sensitivity, factoring in those gains or losses. It is also limited by the ambient noise around the antenna, which togethe with the received signal strength determines the signal to noise ratio. Each modulation has a minimum SNR where the signal is intelligible That’s the one index card almost no math overview but I hope it helps you get pointed in the right direction