Course › Signals and problems
Harmonics and unwanted signals
How to calculate harmonics, and the causes of spurious emissions, splatter and FM over-deviation.
What you will be able to do
- Define harmonics and calculate them
- Diagnose a signal heard on a harmonic frequency
- Define spurious emissions and name two causes
- Define splatter and name the causes for SSB and FM
Why is my signal turning up where it should not be?
Your transmitter should put its power on one frequency. When it leaks onto others, you cause
interference.
Harmonics
Harmonics are signals at integer multiples of the fundamental transmitting frequency.
fn=n×ffundamental
A fundamental of 7.075 MHz with harmonics at 14.15, 21.225 and 28.3 MHz
Diagnosing a harmonic
Spurious emissions
Spurious emissions are unwanted RF emissions outside the necessary bandwidth of a
transmission. Two causes:
- operating a radio without its cover or shielding,
- improper neutralization of a tube-type amplifier.
Splatter
Splatter is when the transmitted signal occupies more bandwidth than necessary, interfering
with stations on nearby frequencies.
- Causes of SSB splatter: excessive speech processing, or microphone gain set too high.
- Cause of FM interference to nearby frequencies: microphone gain or deviation control set
too high. Over-deviation widens the signal.
You now know
- Harmonics are whole-number multiples of the fundamental: the 4th harmonic of 7,160 kHz is 28,640 kHz.
- A signal heard at 21.225 MHz when you transmit on 7.075 MHz is the 3rd harmonic.
- Spurious emissions come from missing shielding or improper neutralization of a tube amplifier.
- Splatter comes from excess speech processing or high mic gain (SSB), or high mic gain or deviation (FM).
Source: RSK Foundation tutorial, KARE 07 §4