The correct FM receiver antenna length

The antenna length of your receiver is important for best range and for better quality of the reception.

There is a mathematical formula to determine this length:

t=c/l

where:

t=antenna length

c= light speed (for this purpose considered to be 300.000km/s, equivalent to 300.000.000 m/s)

l=transmitter frequency

The most usual frequency in R/C boating is 75 MHz. Within this frequency there are 30 available channels, with frequencies between 75.410 MHz and 75.990 MHz. As you can easily see in the formula, the higher the frequency the shorter the antenna length. Let's check the right lengths for our
receivers, considering the available frequencies.

For the shorter frequency of the range (75.410 MHz)

·             t=300.000.000/75.410=3.97 meters =156 inches

For the higher frequency (75.990 MHz)

·             t=300.000.000/75.990=3.94 meters =155 inches

From this formula, two observations arise:

·             the difference in length from the higher to the shorter frequency is negligible - 1 inch in 156";

·             it's impossible use in a boat the antenna length calculated by the formula.

And so, should we forget the ideal length idea?

Not necessarily. Scientists discovered that sub multiples from the ideal length can be used with almost no loss. So, 1/2, 1/4 or 1/8 of the calculated length are almost as efficient as the original. So:

·             156/8=19 1/2" 

·             155/8=19 3/8"

19 inches and fraction, close to the length we find in our receivers.

And how about the 27 MHz frequency?

Using the same formula, you get 54 inches for 1/8 wave or 27 for 1/16.

Science has a solution for (almost) everything.