The receiver antenna is an end-fed long wire and there is an antenna matching circuit in the receiver designed to transfer maximum energy to this "tuned" antenna. THE LENGTH OF THE WIRE ANTENNA ON THE RECEIVER MUST NEVER BE CHANGED!  If it is ever shortened or lengthened, its sensitivity and therefore its range will be reduced. In the interest of "neatness" some modellers fold the excess wire back on itself so the loose end doesn't flop around. This is the same as snipping off that much wire AND SHOULD NOT BE DONE! If  by some freak accident the antenna gets broken off, make sure the new one installed is exactly the same length as the old one.

On large models the antenna is sometimes mounted inside the fuselage, often in a plastic tube mounted along the length. This is OK as long as there are no metal pushrods or other metal parts nearby, but for best and cleanest signal reception an outside location is preferable.

Unlike the receiver, the transmitter antenna is a ground-plane vertical and has characteristics that few flyers recognise unless they are familiar with verticals. Their energy radiation pattern in free space is omnidirectional, meaning in all directions parallel to the antenna ... unless being used near a large mass of metal such as a metal building, which can distort the pattern. The
antenna itself is only part of the system while your body becomes the rest. To prove this, if your transmitter has an RF output indicator, turn the transmitter on and set it alone on a non-metallic surface.  Note the output reading. Now pick it up and hold it as you do while flying and note the increase in RF output.

Also, there is a "cone of silence" directly off the tip in which far less radio energy is radiated. So when your model gets too low and far away and begins to lose the signal,  do not point the tip of the antenna at it! Rather, hold the transmitter above your head at arm's length with the antenna as nearly parallel to the receiver antenna as you call manage. This will sometimes re-establish radio contact, and save your model. It is also the reason why,  if you want to see your model's performance "hands-off", you point the tip of the antenna at your model.

During a "range check" (which must be done regularly) the transmitter antenna is not extended and should be pointing directly at the model to indicate the minimum range available.

One final reminder:  Always make certain the transmitting antenna is fully extended before taking off. It is an easily neglected step which de-tunes the antenna and can shorten the radio's range dramatically.  Like the strings on a musical  instrument, an antenna must be tuned to the proper electrical length to resonate at its intended operating frequency. To change its physical
length without retuning the loading circuit will throw it "off-key", as it were.

Substiture transmitter antennas need to be carefully selected otherwise signal radiation is inferior. Please be careful with maintenance of all antennas as if you have an accident it may be me that you injure!