It goes without saying that maintaining control of your aircraft is the most critical part of your FPV system. As you venture out further you gradually reach the limits of hobby R/C systems. "UHF" systems made specifically for the FPV market will provide you with plenty of range but are much more demanding in terms of proper installation and in many parts of the world will suffer interference because they operate on public bands with relatively low output power.
Regardless of frequency and R/C system you are using, there are a few things you can use to stay in control of your aircraft longer. The general idea of all these tricks is to artificially limit the range of your R/C system so you can increase it when you do notice loss of control. As a side-effect you also gain the ability to estimate the capabilities of your R/C link.
Transmitter antenna positioning
Almost all R/C Transmitters are equipped with so-called "whip" antennas. The antenna is a "stick" with the signal coming out of the antenna being the strongest at the sides and the weakest along the path of the antenna (top and bottom). This means that pointing your antenna directly at the plane will give you the least amount of range. As announced earlier, this is our recommended way of flying. If you have your antenna pointed vertically into the sky this will give you the best transmission range. When you point your antenna directly at your plane you artificially limit the range and you can raise the antenna to regain control when you lose the R/C signal. At that point you also know that you are at the limit of your R/C range. If you find yourself losing the link while holding the transmitter vertically, immediately raise the transmitter as high as you can into the air, while keeping the antenna vertical. This will also increase your transmission range once more. In short, it's a poor man's "high power button".
RSSI and OSDs
State of the art OSDs provide a port to connect an RSSI signal to. The RSSI - Relative Signal Strength Index - tells your OSD how much range you have left on your signal. This is possible both for video and for R/C, but is most commonly used for R/C signals. Not all receivers provide the RSSI signal out of the box. They require modification that will void the warranty. Searching the internet for guides on how to extract the RSSI signal from your receiver will usually yield good results. If you're purchasing a new receiver, check if there are detailed instructions available on how to obtain RSSI information. Some of the older OSDs require you to calibrate the RSSI percentage values. Be sure to set 0% to a link-quality where you can still control your plane, and if available have warning indicators on your RSSI signal to warn you before you reach 0%.
Boosting your R/C signal using either built-in booster switches, firmware updates or external amplifiers is recommended ONLY if the booster can be enabled and disabled during flight. State of the art FPV R/C systems come with an emergency booster button that roughly doubles the range of your R/C system for a short period of time. This allows you as pilot to regain control in the event that you have exceeded the maximum range or gives you more leverage to overpower any interfering sources. Use the boosted signal only until your plane is back in safe operating range. We advise against use of fixed-power boosters as they set your range to a fixed distance. Variable distance is always better, not in terms of absolute range but in terms of safety.