Antennas for TCP/IP over UHF

For best results, follow all general VHF/UHF antenna considerations, plus these additional recommendations specific to UHF:

• Vertical placement
  • Antenna height is the most important factor. Place the antenna as high as possible. Make it the highest antenna you have at your site to avoid obstructions that can cause multipath interference. Place the antenna at a different height from other antennas to avoid desense.
• Horizontal placement
  • Place the antenna as far away as possible from obstructions and other antennas to avoid mutlipath and desense. On larger buildings, sometimes one end of the building is better than the other. At a minimum avoid any nearby obstructions.
• Gain
  • Use an antenna with as much gain as possible. Typical tri-band antennas have a gain of about 9 dBi for the UHF band, which should be sufficient. If you are installing a dedicated antenna, then higher-gain options are available.
• Coax
  • Keep the coax as short as possible, Use at least LMR-400 or equivalent. For longer runs, use LMR-600 or hardline, such as 1/2" Heliax (e.g. LDF4-50).
• Connectors
  • Use N connectors wherever possible.
• Be sure to use a proper Lightning Arrestor

All general VHF/UHF antenna considerations apply to antennas used for UHF data networking

The transmitter output power for commercially available UHF data radios are typically limited to 10 Watts. Because of the lower power and higher frequencies involved, the following additional considerations also apply:

• Signal to Noise Ratio
  • The data rate is highly dependent on the signal to noise ratio (SNR). For data rates capable of supporting TCP/IP, the SNR required is typically 25 to 32 dB (higher is better). By comparison, a "full quieting" FM signal typically has an SNR of about 20 dB. So, high speed data radio connectivity requires a much better signal than is needed for voice communications.
• Multipath
  • As frequencies increase and wavelengths decrease, the effect of multipath interference increases. UHF frequencies are more susceptible to multipath than VHF frequencies.
  • Although 100% clear line of sight is not required at UHF frequencies, obstructions in or near the path can create multipath interference. So the antenna path needs to be as high and as free of obstructions as possible. At a minimum, it should be as high as possible above surrounding buildings and other obstructions.
• Desense
  • A lower transmit power means the received signal will be weaker. So any desense from signals radiated by nearby antennas will have a greater effect.
• Coax
  • To maintain the highest SNR, the path between the radio and antenna needs to have as little loss as possible. A minimum of LMR-400 is recommended. Higher quality coax, such as LMR-600 or hardline, such as Heliax (e.g. LDF4-50), can significantly reduce loss at UHF frequencies.
• Connectors
  • The PL-259 (male) and SO-239 (female), so called "UHF" connectors, which are commonly seen on amateur radio gear, aren't really designed for UHF. They are not 50-ohm connectors and, at UHF and higher frequencies, exhibit higher loss by reflecting more of the signal. N-type connectors, such as N, BNC, and TNC, are constant 50 ohm connectors and reflect less power, resulting in lower loss. The bayonet-style mounting of BNC connectors can exhibit some signal leakage and loss when wiggled and are not recommended. N-type screw-down connectors, such as N or TNC are ideal. TNC connectors are usually found on devices (like the radio), while N is usually used everywhere else in the cable system.