[UK-CONTEST] CW in V/UHF contests

[David G3YYD]

I have tried to work this out before and below is how I thought about it.

Assume just noise, no QRM and for reasonable copy both SSB and CW 
require the same signal to noise ratio. Previous studies have shown that 
an experienced CW op has an ear brain bandwidth of 50Hz.  Lets assume 
2KHz bandwidth for SSB as being representative of a typical V/UHF RX. 
The CW op will experience 40 times less noise power than the SSB Op 
which is a 16dB advantage to CW. Average power output on CW is about 60% 
of PEP while RF Clipped SSB is about 30%, however dedicated VHF/UHF TXs 
do not use RF Clipping in which case average power is 10% or less. On 
transmit power there is at least 3dB advantage to CW. Sabin in his RF 
Systems book says for no dynamic range compression a male voices average 
power is -11.5dB of peak power with it being 15dB after pre-emphasis is 
added.

The above shows that CW is around 20dB better than SSB and may be more. 
On 2m once the range of a pair of stations is greater than 300kM  it 
requires a system gain increase of 11dB to increase tropo range by 
100KM.  In which case CW tropo range should be 200Km greater than SSB. 
If your SSB station has a range of say 600KM then CW should be reaching 
out to 800KM on 2m. An added benefit is that probability of QRM on CW 
with proper narrow filters in the RX is way down on that for SSB.

To see what this means to you. On a western EU map draw a range circle 
at your normal SSB tropo range and then another 200KM further out. This 
will give a true idea of what becomes workable on CW compared to SSB.

73 David G3YYD


On 28/05/2011 07:53, Chris G3SVL wrote:
> What is the>  estimated>  'gain' of a CW signal over a SSB signal ? 10dB 20db ?
>   >  Robert F5VHN G0HGW
>
> At 08:25 28/05/2011, cris at gm4fam.plus.com wrote:
>> That is an interesting question Robert!
> Cris, Robert,
>
> There was an article on that very subject in a mag last year.  Can't
> find it in QST archives so maybe I saw it in someone's CQ mag.  Any
> CQ mag subscribers remember it?
>
> 73 Chris, G3SVL
>
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