[TowerTalk] perspective

[Tom Rauch]

Hi Brian,

> It went like this.  If it takes a certain power to make a given path and
> you only have half that level, you won't make it.  If you increase 3db you
> will--ignoring the abilities of the hardware or operator to copy signals
> beneath the noise.  The moonbounce guys used this accounting method all
> the time to judge their chance of success.  

That's works well if noise is the limiting floor, the path is well know 
in all characteristics, and fading is well known. All parameters have 
to be very well known. 

Outside of those conditions, it doesn't work at all for predicting 
who... or how many "who's".... you can work.

Yuri touched on that pretty well. What happens with earthbound 
contacts is a bit less ERP might mean it would take a bit longer to 
work a few stations, and on a rare occasion you might even 
randomly miss someone.

Unlike moonbounce, it wouldn't apply at all for receiving. When 
receiving at HF, gain doesn't matter. The antenna pattern and the 
direction of unwanted and wanted signals is all that matters.

At HF, the optimum receiving antenna is commonly not the highest 
gain antenna. Not so with the moon.

> The contester who is serious is trying to stack the odds in his favor. If
> 1 or 2 db will more than likely produce a few contacts or multipliers
> more, he will probably go for it.  Many contests are decided by a few
> contacts.  For what it is worth, August QST shows W4MR and K3KO with a
> score of 101,634 points in the last 160M contest.  The number of QSO's and
> multipliers were identical. (It is just a friendly cross town rivalry). I
> can't say that 1 or 2 db would absolutely have helped either one of us. 
> It MIGHT have resulted in another multiplier or QSO which would have
> broken the tie.

....and you might have lost a multiplier or a few QSO's by having 
too much directivity at the wrong time! 

(On 160 meters) We can get 6 dB or so gain by using a phased 
array, yet we almost always use an omni-vertical to avoid losing 
contacts.

The only time we use the maximum directivity available is when we 
do a run of Europeans or Japanese, and even then it only works 
really well when conditions are stable and we can focus everything 
on the DX in one area.

Big antennas really help me work a pileup or a single station IF I 
know what direction to listen, yet they often are not best for a 
contest!

Now if I was working moonbounce, focusing would be everything. I'd 
know exactly where all the signals and all the noise was coming 
from and how loud each should be and could predict how many 
more stations are available for a given gain increase.

The problem is know how much. Mike had a good suggestion, vary 
power in fixed short intervals without telling the operators what is 
going on, and look at the rate and multiplier change in each short 
period. That should work.


73, Tom W8JI
w8ji@contesting.com

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