By Stan Yeo

The reason for writing these notes are that we are very concerned about the possible consequences of modelers using inappropriate receivers for general flying i.e. using receivers which in our view should only be used for lightweight indoor models and small park flyers. Using a low performance receiver (Rx) will one day result in a serious accident with serious legal ramifications, particularly if the user was aware of the Rx's limitations or was advised by the retailer that it was 'full range' and suitable for general flying!

Below are some simple rules to determine if a receiver is 'full range' or not. If a receiver satisfies any of the rules then, in our view, it is NOT full range and does not have the necessary 'selectivity' and is only suitable for use in lightweight indoor models and small park flyers. The issue is not necessarily range (a number of modelers often tell me they have 'specked out' some of these Rxs) but one of selectivity i.e. the receiver's ability to separate your signal from other signals that are present on or near your frequency. The more radio frequency noise there is around your channel then the harder the Rx has to work and the shorter the range will be. It is worth noting that for selectivity reasons a number of clubs operating indoor / small park flyer models operate a 20 kHz channel spacing rule.

1. Any Rx that takes a half size crystal or weighs less than 15 grams. Indicates Rx has been built with strict weight limitations. Miniature components are less efficient than their larger sisters particularly tuning coils.
2. Is marketed as suitable for 35Mhz or 40Mhz simply by swapping crystals this indicates that the receiver has a wide bandwidth and hence poor selectivity.
3. Has a half length Rx aerial (normal aerial length is 900 - 1000mm).
4. Has less than 5 active filtering components i.e. tuning coils and ceramic filters. Tuning coils are normally housed in a metal 'can' whilst ceramic filters look like rectangular plastic blocks.

These notes are based on personal experience and technical knowledge gained during a number of years manufacturing radio control equipment in the 1970s and 80s and are not intended to denigrate any products currently on the market but to assist modelers in choosing the most suitable Rx for the model they are building. A golden rule is to match the quality of the radio equipment to the value of the model where the value of the model relates to time and money it cost to build. It is worth mentioning that in a recent article on receivers in the BMFA News the contributor commented show me a £20 Rx that performs as well as a £60 Rx and I will stop buying £60 Rxs, or words to that effect.