[UK-CONTEST] CW in V/UHF contests

[Robert Chipperfield]

Hi David (and others),

A nice analysis! I'd certainly agree with you in terms of improving 
"best DX", but of course, that's not what the contest is scored on.

At the moment, I would suggest that the majority of stations active in 
the UKACs aren't equipped for (or at least readily able to operate) CW. 
So, if I can run at three times the rate on SSB as CW, even if my 
potential contact area is reduced by 40%, I end up with a better score 
sticking to SSB, at least until I've exhausted all those stations I can 
work, which typically doesn't happen at least in 2m or 70cm UKACs in the 
available time. This is a simplistic analysis, of course, particularly 
with respect to multipliers, but I think the logic holds, if not the 
exact numbers.

It's a self-fulfilling prophecy: all the while significantly better 
rates (and thus scores, within reason) are to be had on SSB, there's no 
incentive to ensure you're always ready to go on CW (more of a 
consideration for those who operate /P) or even to improve our CW for 
those of us who definitely aren't able to claim the 50Hz brain 
bandwidth. If CW did become the norm, or at least a substantial 
proportion of QSOs, then I suspect the balance would shift further in 
its favour as a result.

Now, the above may not apply in the more European-oriented contests, or 
indeed in contests significantly longer than the UKACs, where rate may 
be less of a factor, but at least one of the earlier posts made 
reference to UKACs, so that's what I've considered here.

Cheers,
Rob

On 28/05/2011 11:01, David G3YYD wrote:
> 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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