Unless you have an incredibly poor antenna or an incredibly poor
receiver, you'll never hear the receiver noise on 80 meters because the
atmospheric noise is much greater. There are a number of sources of this
noise, man-made and natural, and its level varies a great deal. It's not
the same as loss, and although it's a "receive end" problem as you say,
it's nothing you can improve by altering the receiver. There's just a
little about it in the ARRL Handbook, but I'm sure a web search will
reveal a great deal of additional information.

Apparently you assumed that the atmospheric noise is zero. That's not a
valid assumption at HF.

I still wouldn't be surprised at a 40 mile contact with 7 mW however.

Roy Lewallen, W7EL

Peter Barbella wrote:
Hi Roy,

I made no assumptions about the atmosphere, neither loss, nor noise.

I did assume that my antenna is about 0 dB gain and I further assumed about
10 dB loss for the temporary wire running through the wall of my house to
the antenna (just a simple piece of wire running up a maple tree). I
thought the 10 dB would be generous.

I assumed that the antenna of the person receiving was also 0 dB and I
assumed that his receiver would have a sensitivity of about -80 dBm. I
think that's pretty conservative. I would guess that modern receivers go
well under -100 dBm for sensitivity; especially for CW operation.

As I said, I assumed nothing about atmospheric loss. I'm not quite sure
what atmospheric "noise" is. Where does that come from? Is it what you
call atmospheric loss, or is it something else? In any event, I would
consider that to be a "receive end" problem.

I got a not from someone who worked a 500 mile contact with another QRP
crazy who was using 50 micro (not milli, micro) watts. That's amazing. It
gives me hope that I'll get my first contact soon.

Thanks for the reply.

Peter Barbella
KB1LZH


"Roy Lewallen" wrote in message
...

I don't have experience with a power level that low, but I'm curious about
what assumptions you made about atmospheric noise and antenna gain to
arrive at the 40 mile figure.

Roy Lewallen, W7EL

Peter Barbella wrote:

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