**Previous message:**lbrunson@rodgers.rain.com: "How do rigs degrade with degradation of supply voltage"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

I've often been asked questions like "How much will .5 dB in coax

losses hurt me?" or, "What can I work with two watts into a dipole?".

There are a lot of anecdotal answers floating around but I think many of

them are wrong.

To try to get some better answers I did a little data analysis

exercise using results from the recent CQWW cw contest. Whether or not

you're interested in contests, a contest is a good place to get data;

lots of stations with different configurations making lots of QSOs.

Results and station descriptions are usually posted to Internet so I

had lots of information to play with. I made a graph with one axis (x)

as the effective radiated power (in dB relative to 1 watt into an

arbitrary dipole), ERPd. The other axis (y) is the total number of

QSOs made. Both scales are logarithmic. On this graph I plotted four

points -- representing the winners in each of three categories: high

power, low power (150W), and QRP, and the results for my station. I

assumed the three winners used the maximum power allowed in their

class. I estimated their average antenna gain by taking the gains of

their antennas on each band and weighting them based on what percentage

of the total contacts that band accounted for. For example, AA2U has

stacked 6-element tribanders on the upper bands, a 2-el on 40, and a

loop for 80/160. I estimated that this averages out to 10 dBd gain.

The resulting data points were:

Call QSOs Effective Power

(ERPd watts)

------------------------------

K1KI 2927 24000 high power

K2ZJ 1292 2000 low power

AA2U 734 50 QRP

WB2CPU 234 3 me

The points are surprisingly colinear. The only anomaly was that

AA2U, the QRP winner, was a bit over the line that connects the other

three. Since Randy often places in the top ten in the LOW POWER category

while running QRP, this is not unexpected. The line that resulted had a

slope of about 4 log power/log QSOs, i.e., it takes 4 dB of effective

power increase to increase your QSOs by 1 dB's worth. I won't try to

draw it here using ASCII characters, but you can start with a point

representing 1 watt, 300 Q's and draw the line to the right from there

with a slope of four.

From this data I'm concluding the following:

a. Getting rid of losses in coax, antenna switches, etc.

improves things somewhat, but not that dramatically. The line's slope

of 4 dB power per 'QSOs dB' says that reducing your power loss by 1 dB

would have increased your QSO total by about 10 ** .025 ==> 6%. A 2 dB

increase would give 12% more Qs, a 4 dB increase 26%, etc. While the

numbers are only specifically applicable for this contest, they

probably can be generalized to imply a success rate for working

non-contest DX or making readable contacts in general.

b. While you're not going to be competitive with the big guns,

you can make a reasonable number of DX contest QSOs with QRP power and

simple antennas. In this contest the graph suggests that you could have

made over 400 QSOs with five watts and dipoles, and, 300 QSOs with just

one watt and dipoles. Since these numbers were derived mostly by

analyzing the contest winners, they represent the upper bound of what

could be done.

It might be surprising that the line was linear over a very wide

power range, about 5 decades; from about 1 watt to tens of kilowatts.

Actually, my experience indicates that it may be valid even lower than

that, say down to .1 watt effective power.

I hope this information provides a way of estimating the

performance effects of changing station characteristics and encourages

people to try working QRP. To save bandwidth here, I've described

things quickly. I'd be glad to elaborate or discuss other people's

thoughts on the subject.

73,

howie, wb2cpu

howi@world.std.com

**Previous message:**lbrunson@rodgers.rain.com: "How do rigs degrade with degradation of supply voltage"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

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