Heathkit HW-101 Troubleshooting

this ratio, the input signal level must be given. This is usually expressed in microvolts.
Typically a certain input level required to give a 10 dB signal to noise ratio is specified.
It is more usual to see a signal to noise ratio expressed in a logarithmic basis using
decibels:
If all levels are expressed in decibels, then the formula can be simplified to:
The power levels may be expressed in levels such as dBm (decibels relative to a
milliwatt, or to some other standard by which the levels can be compared.
w.1.3. Effect of bandwidth on SNR
A number of other factors apart from the basic performance of the set can affect the
signal to noise ratio, SNR specification. The first is the actual bandwidth of the receiver.
As the noise spreads out over all frequencies, it is found that the wider the bandwidth of
the receiver, the greater the level of the noise. Accordingly the receiver bandwidth
needs to be stated.
Additionally it is found that when using AM the level of modulation has an effect. The
greater the level of modulation, the higher the audio output from the receiver. When
measuring the noise performance the audio output from the receiver is measured and
accordingly the modulation level of the AM has an effect. Usually a modulation level of
30% is chosen for this measurement.
w.1.4. Signal to noise ratio specifications
This method of measuring the performance is most commonly used for HF
communications receivers. Typically one might expect to see a figure in the region of
0.5 microvolts for a 10 dB S/N in a 3 kHz bandwidth for SSB or Morse. For AM a figure
of 1.5 microvolts for a 10 dB S/N in a 6 kHz bandwidth at 30% modulation for AM might
be seen.
Points to note when measuring signal to noise ratio:
SNR is a very convenient method of quantifying the sensitivity of a receiver, but
there are some points to note when interpreting and measuring signal to noise ratio.
To investigate these it is necessary to look at the way the measurements of signal to
Signal to Noise Ratio (SNR) Page 53

Heathkit HW-101 Specifications

General

Brand	Heathkit
Model	HW-101
Category	Transceiver
Language	English