"Peter Barbella" wrote in message
news:2xkTd.30756$ya6.20070@trndny01...
I've built a little 80 meter transmitter that seems to be putting out
about 7 milliwatts. By my caculation, that should be good for about 40
miles. Anyone have any experience with low a power output?

Pete
KB1LZH


Guys,

With this post, I have received several useful suggestions and comments.
Thank you very much.

Many of you are curious about the assumptions I made when I made my
calculation of 40 miles. I simply went with something I know: the radar
equation. I made a simple adaptation to the radar equation.

It starts with a simple premise that the power in my transmitter will be
radiated equally in all directions. That is equivalent to a zero DB gain
antenna. I assumed that the receiver will have a sensitivity of -80 dBm. I
then, simply applied the basic fact that power diminishes as the square of
the range. That leaves a power density at any given range of P divided by 4
pie R*2. (Forgive the lack of an equation editor)

The next assumption involved the capture area of the receiving antenna. In
radar, the capture area of an antenna is proportional to the wavelength
squared. With a zero DB receiving antenna, the capture area would be simply
lambda squared divided by four pie.

With those simple assumptions you can determine the amount of power
available for a receiver. Since my little transmitter is a simple
breadboard with three transistors and a wire that runs out of my house and
up a maple tree, I made a further assumption that I have about 10 DB of loss
delivering my transmitter power to the antenna.

That 10 DB loss along with the assumption of only minus 80 dBm sensitivity
in the receiver seemed pretty conservative to me. Most receivers can
probably do much better, especially with CW operation.

Of course, as RegEdwards has pointed out, what is really needed is a good
benchmark. Several of you provided me with some interesting benchmarks.
Thank you very much for your replies.

Regards,
Peter Barbella
KB1LZH




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