Keith:
As you have no doubt seen from the other posts, you can do a lot with
QRP on the low bands. As is clear from such feats as working
intercontinental DX with 5 W on 160 m, QRP is limiting, but not severely so.
I've done some NVIS calculations for New England. If you're
interested in working stations within 200 miles, you can do so
practically every night on 80 meters with 5 Watts to an inverted-V 20
feet high at the apex.
If you're interested in DX, it is slightly more difficult, but far
from impossible. If you could get up a full-size 40m dipole 30 feet
or more off the ground, you'd be able to work Europe on 40 m QRP most
(but not all) evenings. (Caution: 40 has a tendency to go dead
between about midnight and sunrise. The flux is presently so low that
the MUF to most locations drops below 7 MHz late at night. In that
case you cannot work DX on 40 no matter how much power you run.)
On 80 meters I have a dipole up about 40 feet. My experience this
winter is that about two nights out of a week, the 80 meter DX
opening at sunrise in Europe is strong enough that I can make
contacts with 5 Watts.
A couple of practical thoughts:
Back when I worked in the RF Group at Oak Ridge National lab, we had
a sign on the wall that said, "A dB is a dB is a dB, and every one is
just as good as all the others, no matter where they come from." With
that in mind, and considering that you're giving up 13 dB by reducing
transmitter power from 100 to 5 Watts, you need to think about were
else you can pick up some extra dBs. For example:
1) Put up the biggest highest antenna that you can. If you have a 20
foot high antenna, but could raise it to 25 feet, do so. It is worth
the trouble doing.
2) If you cannot make your antenna system work for you, at least try
to get it where it does not work against you. Avoid wave traps and
tuning networks if possible. If you must use a Tuner or a matching
network, make it out of the heaviest components you can; you want to
minimize losses. Use the biggest transmission line you can afford and
run it with the lowest SWR you can achieve. Make as direct a run from
the transmitter to the antenna as possible, with as few breaks in the
line and as few items inserted into the line (filters, directional
couplers, ferrite baluns/isolators, etc.) as you can get away with.
3) In keeping with the above principle, you might want to try to set
up dedicated 80 and 40 meter antennas and not worry about the high
bands for the next couple of years. Multiband antennas will always be
lossier than single band antennas.
4) Listen for the very loudest DX signal you can find and call that
one. If one DX station is is markedly louder than the other DX, he's
likely using a high gain antenna. One of the best tricks in QRP DX is
making the other guy's high gain antenna work for you.
5) Your biggest source of extra dBs is the ionosphere. Use VOACAP to
compute when the strongest openings from your location will occur,
and operate at those times. (VOACAP is downloadable for free. It is
well documented and easy to learn. To find out more, simply Google VOACAP.)
73,
Steve
AA4AK
At 12:19 PM 1/11/2006, Darwin, Keith wrote:
K1 or K2. Hmmm, the debate continues. But wait, we're approaching a
sunspot min. My antennas are pretty limited. I have a 28 foot vertical
(fed with a tuner near the base) for 40 thru 15 and a dipole at 25 feet
but that is about it. No towers, no high wires, no yagis.
How limiting will 5 or 10 watts (even with that Elecraft Mojo) be under
current conditions? Are we entering into conditions where QRP with
simple antennas will become rather frustrating? Is it K2/100 time?
- Keith KD1E -
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