Radio Frequency or RF Link refers to the radio connection between transmitter and receiver. The link needs to be solid at all times if the pilot is to retain control of his aircraft and hence the following table.
Causes and Fixes of RF Link failure
You can see from the table below, that while the 30 yard range test is an important tool, on it’s own it is simply not able to guarantee a bullet proof RF link.
The majority of items on the list all require that the pilot does more work to ensure all is well before flying.
The good news is that all of the possible causes below can be checked out by the model pilot and the ways for doing this are briefly included in the article and developed further in associated articles; the links for which are at the bottom of the page.
If these methods are used, the user will very likely achieve two things.
1.) The user will establish whether his equipment and installation has a bullet proof RF link or not and so know whether it is safe to fly.
2.) In the event that equipment faults, hard or marginal, are discovered, he will have solid evidence of the problems encountered assisting his claim for replacement parts from his equipment manufacturer.
All that said, the means of testing our equipment thoroughly is available but as you might expect by now, it requires more than the thirty yard range test.
| No. | Cause | Detail | Fix | Will a 30 yard range test identify the RF Link failure ? |
| 1 | Non functioning receiver. (Rx) | e.g. caused by crash damage. | Replace the Rx | Yes |
| 2 | Non functioning transmitter. (Tx) | e.g. caused by dropping the Tx. | Replace the Tx | Yes |
| 3 | Partially functioning Rx | e.g. caused by Rx antenna damage. | Replace the Rx | Probably not |
| 4 | Partially functioning Tx | e.g. caused by Tx antenna damage. | Replace the Tx | Probably not |
| 5 | Bad Rx installation. | 1. Rx antennae not polarised. 2. In aircraft Rxs badly positioned giving poor diversity 3. Rx's antennae blocked by carbon fuselages or metal skinning. 4. Rxs exposed to in aircraft electromagnetic noise i.e. antennae buried in servo wiring. 5. In aircraft metallics, e.g. engine, batteries, too close to Rx antennae causing RF blocks and reflected signal fading. | 1. Correctly polarise the Rx's Antennae 2. Where radio systems use satellite receivers, correctly position in aircraft Rxs and satellites to give needed diversity. 3. Ensure Rx's antennae are mounted outside carbon or metal skinned fuselages. 4. Correctly separate Rx's antennae from servo wiring etc. 3 inches. 5. Correctly separate in aircraft metallic objects from Rx's antennae by 3 inches min. | Probably not |
| 6 | Radio signal blocking. | e.g. aircraft flies behind a substantial and solid object. | Avoid flying behind solid objects. Largely intuitive. | No. Note: This is not the Range Test's job, and is only included for completeness. |
| e.g. aircraft fuselage contains significant amounts of carbon. | Ensure Rx antennae are routed external to carbon fuselage, or fit a purpose designed Rx for this issue. | |||
| e.g. aircraft is metal skinned. | Ensure Rx antennae are routed external to metal skinned fuselage, or fit a purpose designed Rx for this issue. | |||
| 7 | Reflected signal fading. | e.g. metallic objects in the aircraft, e.g. engine exhaust, can cause duplicate reflected signals to arrive at the Rx at the same time. If these are exactly 180 degrees out of of phase then they cancel and the RF Link is broken. | Maintain good separation between Metallic objects in the aircraft and Rx antennae, 3 inches plus. | No. Note: This is not the Range Test's job, and is only included for completeness |
| 8 | Tx battery failure while airborne. | Always check battery levels | No. | |
| 9 | Rx battery failure while airborne. | Always check battery levels | No. | |
| 10 | Incorrect use of the Tx's antenna. | If the Tx antenna is pointed directly at the aircraft, the dead spot of the RF spread pattern, i.e. the axis of the doughnut spread, is pointed directly at the aeroplane, i.e. very weak signal strength. Do this long enough and the aircraft will throw a hold and the receiver will initiate the failsafe protocol. Note: this does not apply to Txs with stub antenna, i.e. where the Tx housing contains two polarised antennae. | Ensure single antenna transmitters are correctly folded so the aeroplane's Rx always sees maximum signal strength. | No |
| 11 | Rx battery supply brownouts | Caused by excessive electrical loading of in flight batteries. e.g. high power servos dragging the supply down to the point where the Rx shuts down. | Ensure Rx supplies can meet worst case supply needs in amperes and ampere hours and still have adequate margin in reserve. | No. |
Related Article Links:
2.4 gHz. RF link problems 1. New equipment failure.
2.4 gHz. RF link problems 2. Tx/Rx RF link principles.
2.4 gHz. RF link problems 3. Advanced Range Test Protocol.
2.4 gHz. RF link Problems 4. Causes and Fixes
2.4 gHz. RF Link Problems 5. Failsafe Triggered
2.4 gHz. RF link Problems. 6. Failsafe Strategies.
