Sunday, October 9, 2011


Fact or Fiction


This Info was obtained from the HF Pack Users Group

Bonnie Crystal KQ6XA, VR2KQ6XA

KQ6XA Rule of Thumb: CW v. SSB Power Effectiveness Comparison

CW -vs- SSB Power Effectiveness Comparison
KQ6XA Rule of Thumb:
5 Watts on CW gets out like 100 Watts SSB.
1 Watt on CW gets out like 20 Watts SSB.
250mW on CW gets out like 5 Watts SSB.

For those who are interested, here is the background
of RF engineering/guestimation/field experience behind
this Rule of Thumb, and the given conditions:

Operators = skilled, talented operators
Language = American English
CW Speed = 15WPM
Bandwidth CW = 1kHz
Bandwidth SSB = 2.7kHz
Signal/Noise Ratio CW = -1dB SNR a Talented CW Ops
Signal/oise Ratio SSB = +12dB SNR a Skilled SSB Ops
5 Watts Power CW = 37dBm
100 Watts Power SSB = 50dBm
Difference = 13dB

Note: Some tricks can be played with CW or SSB to
skew this comparison. Things like bandwidth and
super-operator talent (contest ops), language
(Japanese is 3dB better than American English),
speech compression, morse speed (coherent CW is better),
and types of noise or fading present. For those
wondering about DSP noise reduction... most of the
super-ops who can copy either CW or SSB at abnormally
bad noise levels, don't use DSP noise reduction to do it!

I would love to hear some comments on this comparison
73 de N4LA

1 comment:

Sverre Holm said...

I think this comparison is fair. I wrote some time ago on my web site:

"The gain over speech (SSB) is due to an increased signal to noise ratio. First the noise falls since the bandwidth is reduced from about 2500 to about 250 Hz (conservative estimate) or 10log(2500/250) = 10 dB. Second, CW is either on or off, but SSB has a peak-average ratio of 6 dB or more depending on compression, so this gives a corresponding loss in signal level. Combined this may give a gain of at least 10 dB and probably closer to 18 dB which is 2-3 S-units or a factor of between 16 and 40 in power."

This is not an exact science so your factor of 20 is more or less the same as my estimate of 16-40.

Sverre, LA3ZA