"Spajky" wrote in message
...

with just probably 40mW IMHO (not 40 microW)

Yeah, 40 microwatts, really.

I probably should hasten to add that this was not a random QSO. The
transmitting station has been sending a beacon at various times,
frequencies, and power levels for several weeks. There have probably been
several hundred stations listening for that beacon. While this particular
one was the best on 80 meters, it really isn't all that much of an outlier.
Plenty of other stations were in the same general neighborhood on other
nights.

It did surprise me to see this on 80, though. As Roy points out, the
absence of atmospheric noise is not a valid assumption on HF, and noise does
increase with decreasing frequency. This is exactly the opposite to your
radar experience where it is all about receivernoise. Even at 10 MHz, the
most basic receiver will be sufficiently sensitive that it is limited by
atmospheric noise. This seems to be a particularly bad winter for noise on
80, although there have been occasional evenings when the conditions have
been pretty astonishing.

Also, the noise causes in the lower HF region tend to be somewhat different
than those in the upper HF. Paul Harden made a couple of nice postings to
QRP-L explaining some of that after that quasar whacked us back in December
I think it was. Interesting to note that the news media only picked up on
that event last week. Pretty astonishing, though, that something millions
of light years away could be so energetic as to shut down 80 meters for a
couple of days!

By the way, I see that Paul will be speaking at Dayton (FDIM) this year. I
was planning to go anyway, but it would be worth the trip just to hear him.
This guy *really* understands what space weather does to our propagation.

...

On Sat, 26 Feb 2005 10:29:29 -0500, "xpyttl"
wrote:

It did surprise me to see this on 80, though. As Roy points out, the
absence of atmospheric noise is not a valid assumption on HF, and noise does
increase with decreasing frequency.

However, the noise power is proportional to bandwidth, so if the
throughput rate is not defined, slow down the bit rate to reduce the
required receiver bandwidth, until the noise is weaker than the
signal. While the lower HF noise is not pure white noise, this
principle can still be applied.

For instance on the 135 kHz LF band, it is quite common to use QRSS
with a dot time of several seconds or even a minute and the reception
is done visually on the "Waterfall" (spectrogram) display. Although
the LF transmitter power might be several hundred watts, the
transmitter antenna efficiency is usually much worse than -30 dB, so
the radiated power is well below 1 Werp and the noise level is much
higher than on HF.

Paul OH3LWR

On Sat, 26 Feb 2005 10:29:29 -0500, "xpyttl"
wrote:

Yeah, 40 microwatts, really.

I probably should hasten to add that this was not a random QSO. The
transmitting station has been sending a beacon at various times,
frequencies, and power levels for several weeks. There have probably been
several hundred stations listening for that beacon.

oh, that was the case ...

.... well, I recalculated reached distance for usuable everydays
connection in real normal conditions with average equipment
/forgetting the extremes!/ (after some additional thinking reading
these posts) to even simplier formula than before & more realistic (a
bit larger distances reached) as follows:

to reach the distance of ONE full wavelenght (ex.80m for 3,75MHz) you
approx. need Rf RMS voltage on TX out for antenna (50ohm) :

1mV - for narrowBand unmod.carr.CW
3,16mV - for ordinary CW & SSB (+10dB)
10mV !! - for ordinary FM & AM or other (another +10dB = +20dB)
30mV - for PacketRadio - for no data loss (+ another 10dB)

.... so original poster (Peter) could get out of his set normally 5Km
for sure (more than 3 miles with his 7mW-atts).

IMHO this is some kind of reasonable expectations about recieving
range ... bye .. :-)
--
Regards , SPAJKY ®
& visit my site @ http://www.spajky.vze.com
"Tualatin OC-ed / BX-Slot1 / inaudible setup!"
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