When it comes to choosing the right UHF CB aerial, size is important, but it's probably not what you think. Taller, with higher 'gain' isn't always better. It's a common misconception that a tall CB aerial gives the longest reception and transmission range in all situations.
Since the UHF band covers a much larger range of frequencies than VHF, 1/4-wave antennas can range anywhere from 3 to 6 inches (7-15 cm) in length, so using the proper length antenna is somewhat more important. For a system operating at 500 MHz, a 1/4-wave antenna should be about 6 inches (15 cm).
The higher the frequency and the shorter the wavelength, the shorter the antenna can be made. When the length of the antenna is 1/4 of the wavelength, the transmission and reception conversion efficiency of the antenna is the highest.
Radio transmission efficiency generally increases with diameter and length of the conductor, but increased antenna length or weight can adversely affect animal behavior.
What to look for when buying a UHF
The first thing to look at is how much are you going to rely on this unit, if it is an everyday thing, don't skimp, quality of audio, volume of Audio and brightness of the screen are going to be key things to look out for.
At a minimum, the antenna should be above the rooftops of local buildings. 30 feet of height is easy to achieve with commercially available, lightweight, collapsible, fiberglass masts. A taller mast is better than a shorter mast.
The most effective antenna has the same length as the length of the wave it is used for. For practical purposes, half or a quarter of that length will suffice. Most LoRa antennas are a 1/4 wavelength.
The wavelength of a signal should always be 1/4 the length of the antenna you're using, as this gives you the very best efficiency. While you don't have to pick an antenna whose length is exactly 4 times the wavelength of the signal, it's a good idea to get as close as you possible can.
You also want the antenna to be at least 1/4 wavelength long for each band you plan to use. For instance, to work 40m be sure the antenna is at least 10m or 33' long.
Signal Strength
A good rule of thumb is that a short-range antenna is probably fine if the tower transmitting the signal is less than 40 miles away. However, if the signal is weak, getting a long-range antenna can help you pick it up clearly. You can check signal report sites to determine what kind of signal to expect.
Antenna Length & Type: Everything else equal, longer antennas will always have a longer range than shorter antennas. Also, certain types of antennas have a longer range than others.
Yes, an antenna can be too long. The length of an antenna is directly to the frequency. Too short or too long will not be at the “resonant” frequency and will result in a high Standing Wave Ratio (SWR). That will reduce the efficiency and could certainly lower the S/N (signal to noise ratio) for the radio.
Since UHF transmission is limited by the visual horizon to 30–40 miles (48–64 km) and usually to shorter distances by local terrain, it allows the same frequency channels to be reused by other users in neighboring geographic areas (frequency reuse).
The dual antenna technology means you always receive the strongest signal automatically whether you're in the high country, on rough terrain or on the flat.
Prevent Signal Blockage
The 5th wheel will likely be blocking it unless you're using an extremely long antenna. That's when having two antennas comes in handy. With antennas on both sides of your vehicle, you're much less likely to have large dead spots because the antenna system can "see" more.
Wire Antenna
Cut a stranded or solid core wire to the proper length for the module/frequency: 433 MHz - 6.5 inches, or 16.5 cm. 868 MHz - 3.25 inches or 8.2 cm. 915 MHz - 3 inches or 7.8 cm.
It doesn't. The signal strength impinging on the antenna is the same strength, no matter what you do to the antenna.
For example, the common quarter-wave whip antennas used on FM radios in the USA are approximately 75 cm (2.5 feet) long, which is roughly one-quarter the length of radio waves in the FM radio band, which are 2.78 to 3.41 m (9 to 11 feet) long.
Length including spring and base is 96cm.
Heavy duty barrel spring base. 680mm fiberglass whip (full antenna height 962mm) 4.5m Low-loss coaxial cable, a pre-terminated FME connector and PL259 adaptor.
There are certain frequencies that are resonant in the antenna, which is when the efficiency of energy reception is highest. This frequency is determined by the length of the antenna and the speed of light in the antenna material.
To boost range, get to an elevated area and use the radio there. Use a repeater – Signal repeaters can help extend range. A repeater receives and re-transmits the signal from your radio with increased power.
The causes mostly come down to the basic idea that the signals reaching the device aren't strong enough. You may be too far from the broadcast location, or something physically blocks the signals. The antenna could be in a less-than-ideal place or facing the wrong direction.
In the case of UHF CB the length of cable is not important as the vast majority of UHF antennas are broad-band and do not need to be tuned.
The general rule of thumb is to place the bottom half of the aerial at a point where it can 'see' the greatest distance, even to the horizon if possible. In other words, the ideal place to achieve this is up on the vehicle's roof line or roof racks.