1. Where the transmitter has a folding single antenna, ensure the antenna is folded optimally so that the aircraft is always bathed in the RF doughnut spread pattern, and never in the RF doughnut spread pattern's dead spot.

2. Where a transmitter has two antennae which are correctly polarised in the case, e.g. one in the stub aeriel enclosure on top of the Tx case, and one at right angles to this in the transmitter handle, the aircraft is bathed in a spherical RF spread pattern and so no orientation is need by the user.

3. Where a transmitter has one antenna mounted in a fixed stub enclosure which is non foldable, then the likelihood is that the flying aircraft will often be in the deadspot of the RF doughnut spread pattern, thus compromising the RF link and probably leading to occasional holds. The reason that this is the case is because the natural hand positions of the RC model pilot place his thumbs on the control sticks, thus orientating the dead spot of the RF spread pattern at about 30 to 45 degrees to the horizontal. Moreover the pilot will often rotate his upper body as he follows the aircraft. This combination of movements frequently points the dead spot at the aircraft. Such an arrangement can work depending on the strength of the RF. That said fixes to the problem are:

a.) Modify the Tx so that the antenna can be correctly orientated by the model pilot.

b.) Replace the Tx.

Equipment which passes the standard thirty yard range test can still fail in the air and issue occasional Holds. Running an Advanced Range Test, ART, before getting airborne lets you know you are really safe to fly. If this followed by a comparison flight test against known good equipment, the user will know if his equipment is marginal or otherwise. See the links below.

While a good SSFH system should be good for more than a mile of range, the RF link will not be as strong at that distance. This is because the intensity of RF energy is proportional to the inverse of the square of the two distances from the transmitter that are being considered., that is the inverse square law applies. Consider three increments of distance from the Tx. Call them x, 2x, and 3x.

If the RF intensity at distance x from the transmitter is I, then the RF intensity at twice this distance or 2x will be I * (1/2)^2 or I/4, similarly the intensity at three times the distance or 3x, will be I * (1/3)^2, or I/9, or one ninth of the original intensity.

This rapid fall off in RF intensity with range eventually leads to a failed RF link and the manifest on our 2.4 GHz SSFH systems is an increase in the rate of lost frames, until the criteria the designers use to determine when they should issue the failsafe command and bring the aircraft down, are met. 

While this may only be of remote academic interest to an RC modeller, the main point is clear, the further away you are from the model, the worse the RF link. So if the model pilot is flying a large model, at distances where the model is just resolvable visually, he could easily be at risk, even with a good RC system that is known to be performing well.

A final point on this if the pilot was flying away from himself when such a Hold was called at such extreme range, it might not be recoverable. i.e. as soon as the system's failsafe recovery time is reached and the receiver looks for restored RF, the aeroplane is even further away and so immediately clocks up another hold.