Signal Dynamic Range: The difference ( as heard by the receiving
station ) between no modulation during key down ( noise floor )
and your modulation peak in dB.
10 dB, very harsh and tiring to listen too. High (noise floor)
including fans, children playing, the tv and in general background clutter
noise.
The other station will ask you to repeat a lot and in general your
contacts will be short lived.
20 dB, decent audio range with very little audio background noise (noise
floor).
This is the minimum you should have and is possible on virtually all
rigs.
30 dB, your contacts will complement you on you audio, sounds smooth
and clear.
Communications in weak conditions will be generally more successful.
40 dB, broadcast quality transmissions. Do NOT confuse this
with the audiophile perception of broadcast quality audio! I won't even
go there.
Do the math on this to see what your no modulation key down power
out will need to be verses 100 watts out modulated peak power.
50 dB, this is where you need to be if you plan on running a Linear
Amplifier.
Poor dynamic range (high noise floor) is the reason most people ask
if you are running a linear amplifier.
Have you ever done the math on a 1500 watt amp verses a 100 watt rig to see what the dB gain is? Just a thought.
The formula for power is dB = 10 Log 10(max power / min power)
example: 10 Log10 (100 watts / 1 watt) = 20 dB
So if you have 1 watt out dead key and 100 watts out on peaks when
you speak into the
mike you have 'just' met the minimum dynamic range you should
have.
Use a good quality power meter designed to cover the frequency you are using to measure your power output.
A few short definitions of dynamic range is probably in order at this point.
(1) Audio Dynamic Range (DR) is best described as
the ratio of the largest signal to the smallest signal in volts peak to
peak, measured at
a given single frequency. The largest signal would be
determined by applying a signal to the unit and increasing the input to
the unit until the unit's
specified total harmonic distortion (THD+N) is surpassed.
The smallest signal would be determined by applying a signal of the same
frequency and
reducing the input until the output of the unit can no
longer be distinguished from the noise floor. This methodology works for
either analog
or digital systems and by measuring either the input swing
required or the output swing given specifies input or output dynamic range
(IDR or ODR)
respectively.
(2) The dynamic range of an audio signal is the difference between the
quietest discernible part of the signal and the loudest undistorted part
of the
signal. It is normally expressed in decibels (dB).
(3) Dynamic range is the ratio of maximum undistorted signal (full-scale
or onset of clipping) to residual noise (noise floor). Dynamic range in
generally measured in decibels (dB).
Note: number (3) This is what I am speaking about when I say Signal Dynamic range.
The formula for voltage is dB = 20 Log10 (max voltage
/ min voltage)
The formula for power is dB = 10 Log10 (max
power / min power)
In looking at all these definitions clearly the concept of the decibel
is very important.
The primary need is in dealing with exponential phenomena. Intervals,
differences or ranges are always ratios and decibels always take the log
of the ratio to make a linear representation of those intervals, differences
or range. In fact using decibels to measure Dynamic Range implicitly shows
that Dynamic Range must be a range from minimum to maximum signal.
What to do:
Use the minimum microphone gain required to drive your rig.
Speak close to the microphone ( 4 inches or less ). Just remember if you can hear it, the mic will hear it.
Use a wind screen or pop filter as it is sometimes called.
If you are going to use a desk or boom mic look for one with good mass ( heavy ) body, use isolation between the mic and the desk or boom.
A note on isolation: For the desk mic the felt pad made for the typewriter
is a good choice. For the boom mic use the rubber isolation mount
not springs which can sometimes cause problems due to resonance.
Be aware of your home station and mobile environment, ambient (noise floor).
Call a local ham on the phone and have them let you listen to your station over the phone or have them record your transmission for you to listen to.
Work with other hams look for a critical ear.
Do not be worried with tonal quality until you have gotten rid of the
background noise.
Ben
KE4TFI