The signal strength of a very high frequency (VHF) receiver results from the sum of all gains and losses along the path. The signal starts at the transmitter, loses power through the cable to the antenna, gains power in the antenna, but loses power through the air along the path. The receive antenna adds gain, but the cable to the receiver adds loss. Poor or low quality connectors also add loss. The receiver preamp adds gain. To improve signal strength, you must understand all the components involved and know how to install, adjust, repair or replace them.
Increase transmitter power. Every transmitter has a legal maximum power that it can transmit. If you have control of the transmit end, maximize the power to the legal limit to improve the receive signal at the opposite end.
Install lower loss cable to your antenna. Depending on the length of your antenna cable and the frequency, changing to a larger diameter cable could reduce the loss by as much as seven or more decibels per milliwatt (dBm) per hundred feet. Lower cable loss means a stronger receive signal.
Tighten, dry, repair or replace defective connectors. Cable connectors can corrode or water can leak into them causing shorts. Connections can work loose with varying temperatures. Defective connections reduce receive signal strength.
Replace antennas with higher gain models. Use the highest gain at the highest elevation above ground allowed for your particular system. Also check for proper polarity and alignment of directional antennas.
Install a low noise preamp. Older VHF systems may have noisy or low gain preamps. A newer, modern preamp can improve signal strength as it comes from the antenna cable.
Always check the FCC regulations for transmitter power and antenna gain and height limits to avoid a possible fine.