What Is A Weak Signal?

Here is a 0.001w spot made using the 0dbm transverter port on the Flex 1500 without a transverter on 20m:

2012-07-24 13:00 G0MJI 14.097085 -25 0 IO83ni +0 0.001 F5MUX IN78qb 601 373

So what is a weak signal?

Is it 1Mw, 0.1W, 1w, 10w, 100w, 1000w?

Perhaps a different way to look at this might be:

If the signal at the receiving station is weak, then it is a weak signal.

Obviously this presupposes the receiving station has made every effort to be as efficient as possible. I know many might disagree. It is true on, say, 30m that 1w could will easily radiate across the whole world.  Yet it is also the case on 70mhz 100w sometimes wouldn't be detectable 100 miles away.

Does this mean then that every 4m Wspr station should run a kilowatt to ensure they give spotters the best chance? No, obviously this would be a ludicrous suggestion. It would also cause problems for other users on the band. However it is probably the case that on 4m 5-10w is required most of the time.  Sometimes more will get you spotted, often it will not. Also there are days (rare) when milliwatts will make it through.

On HF I usually ran much less than 5W. On 70mhz, 5w is a minimum.

A point to consider
: Given the nature of much of the equipment put to use on 4m, more power often means more heat. More heat means more likelihood of drift. Drift stops you from being spotted. One needs to be balanced against the other.