The question
The client had an unconventional antenna they wanted to use for a 400 MHz transmit link over 50 km. Measurements from an on-site test showed the antenna was 15 to 20 dB lossier than a conventional design. Could the link still close, and at what transmitter power?
The analysis
- Path: free-space loss over 50 km at 400 MHz, about 118.5 dB, before any fade margin.
- Antenna: the measured 15 to 20 dB penalty carried through the budget as a range rather than a single number, so the conclusion held at both ends.
- Cases: receiver sensitivity and required EIRP computed for three signal bandwidths (25 kHz, 200 kHz and 1 MHz) at 20 dB and 30 dB of margin, giving the transmitter power each combination would need.
The recommendation
The required transmitter power climbs quickly with bandwidth and margin, and every decibel of antenna loss has to be bought back with transmitter power. The memo showed that recovering the antenna’s efficiency was the highest-leverage fix, and recommended an antenna redesign before any transmitter was sized.
A short, decision-ready memo like this is often all a team needs to avoid building the wrong hardware.