Radio Control History
Here's a brief history of what radio and radio frequency usage was like in the U.S. and Canada for the past 30 years or so. Originally, and for several decades, there was only one frequency band available for both aircraft and surface (cars, boats, etc.) models. This band was situated in the 27 MHz frequency range and only allowed 7 radio controls to be used simultaneously. The seven available frequency channel numbers [not to be confused with channels of control, like a 4-channel or 2-channel radio] were identified by a single colored flag, each color identifying a different frequency. In order to prevent two people from using the same frequency, you could visually 'see' what frequency each pilot was using by observing the color of the flag attached to the radio antenna.
The 27 MHz band quickly became unpopular in the late 1960s and 70s due to the growth of CB radio usage which transmitted on the same frequency range as the radio units. Interference from the CB radios was common, sometimes resulting in the lost of an aircraft.
A few years later the FCC allocated frequency ranges in the 72 and 75 MHz band to be used for modeling and at the same time the HAM operator frequency band (50/53 Mhz) became available for modeling use as long as the operator had a valid HAM radio operators license. The 72 MHz band was to be used for aircraft and the 75 MHz band for surface use. In the 72 MHz band there was only 6 available frequencies which were identified by two-color flags, one of them white, again each flag indicated what frequency the radio system was using. As in the 27 MHz band, conflicts between two or more pilots could be avoided by only having one transmitter in use with that color flag. In the 72 Mhz band, each frequency channel was separated by a 80 kHz margin. For example, the first frequency was known as 'brown and white' and was situated at 72.080 MHz, the next was 'blue and white' at 72.160 MHz, etc. The receivers that could 'listen' to these frequencies with this 80 kHz spacing are known as Hetrodyne receivers or 'wide-band'.
In 1988, the frequency spacing of the radio frequency channels was reduced to 20 kHz which turned the original 6 frequency channels into 50 channels. At this point in time, the frequency flag mechanism was abandoned and each frequency channel was assigned a number, starting at 11 (72.010 MHz) and running to channel 60 (72.990 MHz). What's important to note is that the original 6 frequencies fall in between the newer, assigned channel numbers, and are sometimes referred to as 'half-channels'. At first, only the even channel numbers were available. In 1991, the odd channel numbers were made available. Some flying fields have restrictions today, in that they only allow even numbers (and the newer spread-spectrum radios). This allowed the older, pre-1991 radio transmitter/receiver combinations to still function without interfering with the newer radios. In Canada, there are even fields that only allow every 4 channels, the older 80 kHz spacing, so that even the 'ancient' radios can operate. [in actuality, some of these fields actually use a 5 channel spacing due to the fact that the original channel numbers in Canada weren't always evenly spaced, between channels 32 & 46, and 54 & 58].
Radios that can handle the 1991 standard of 20 kHz spacing between channels are known as 1991 radios or 'narrow band' radios; the receivers are known as Super Hetrodyne receivers. The newer radio receivers are also equipped with dual conversion circuitry that greatly improves signal reception and reduces interference. Some of the cheaper AM radios from Futaba, JR, and some others (especially surface radios) still use a single conversion circuit with some proprietary add-on circuitry to act like dual conversion by blocking out interference somehow. Even with perfect, dual conversion circuitry and a 1991 transmitter at 20 kHz spacing, a 'wide-band' transmitter, on your frequency can interfere completely with the signal controlling your plane causing it to crash. This is why most flying fields or clubs require that everyone MUST use a post 1991, narrow band transmitter for control.
Don't bother buying or trying to use an older, 1991 or older radio systems to control your aircraft, it's just too risky and dangerous for others flying with you. If you've an old one that is pre-1991 but was created after 1988, you might be able to upgrade it to 1991 status, but it's still best if you just get a better radio. They're more reliable and most always have more features. If you've got some older servos, you can use these without problems. Even some of the servos that are 20 years old can and will still work with most modern radio systems. But, similarly to newer transmitters, newer servos are usually much better than anything older. Newer servos are CONSIDERABLY lighter, faster, consume less power, and usually have twice or more torque and speed comparable to any servo created in the 1970's or 80's.
I have personally used mostly Futaba radios over the years and I have found them to be trouble free. I have also tried Airtronics and HiTec which I feel are quality brands as well. Years ago, I used brands such as EK Logitrol and Kraft, of which neither are still in business. As it turns out, most servos from different manufacturers work with most major brand radio systems. The key difference in radio systems are the connectors and wiring used to connect to the receiver in the plane. Most of my planes have a mix of different branded servos and receivers from many different companies, but be careful, especially when connecting different servos and receiver manufacturers together as some of the wiring might be incompatible. If you incorrectly reverse the polarity (+/-) of the wiring, a servo's electronics can be damaged permanently, so be careful when connecting different brands of servos to your receivers.
Recently I have been experimenting with the newer brands, FrSky, Tactic, and Spectrum and I have found that they are very reliable, lightweight, and best of all, some of the code that is internal to these brand's transmitters is open-source and can be modified to change or add features.
