ARRL Propagation Bulletin ARLP034 (2006)

ARLP034 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 34  ARLP034
From Tad Cook, K7RA
Seattle, WA  August 18, 2006
To all radio amateurs 

ARLP034 Propagation de K7RA

Solar flux and sunspot numbers were up a bit this week, with the
average daily sunspot number rising 25 points to 33.6.  Friday,
August 11 had a daily sunspot number of 39.  With more sunspots, the
higher HF bands have better propagation than they did nearly two
weeks ago when the sunspot number was zero on four days in a row.

A coronal mass ejection from the sun was pushed out on August 16.
The result could be geomagnetic disturbances this weekend.  The
predicted planetary A index for August 18-21 is 10, 25, 15 and 8.

We are still anticipating the upcoming solar minimum, but a large
amount of email arrived this week with the news of the first spot of
cycle 24.  It only appeared briefly, then disappeared.  The clue was
the magnetic polarity of the spot, opposite of sunspots from the
current cycle 23.  As time goes on, there will be more cycle 24
spots, and eventually fewer cycle 23 spots.  See the announcement at  A
thanks for the heads-up goes to KO4WX, WD4DUG, WG4R, VK4AAR, K8MP,
N4JA, N2JTX, CT1BOH, and others.

The extra propagation bulletin earlier this week (see if you missed it)
concerning a proposed DARPA project which could disrupt HF radio
communications generated a huge boatload of e-mail.  After sifting
through it all, some of it from retired military or defense
engineers familiar with the VLF transmitters mentioned by Dr.
Rodger, it may be that Ward Silver, N0AX had the right idea when he
wondered how it could be done, when ''the sheer energy required from
the start would tend to rule it out''.

When Dr. Rodger said that ''two of the US Navy transmitters radiate
1 megawatt'', he probably didn't realize that this is the input
power (before inefficiencies are factored in) to the transmitter,
and doesn't reflect the efficiency of the antenna.

David Olsen, W6PSS pointed out that a 2-megawatt Navy VLF
transmitter in Michigan only radiates 1 watt, and the efficiency is
around .00005%.  He wrote, ''As I understand it, the limitation in
achieving efficiency is the coupling factor.  As the operating
frequency is lowered, there's an exponential increase in reactances
such that it becomes nearly impossible to couple energy to an

Ed Bruette, N7NVP mentioned an article about a more efficient VLF
antenna at, but Ed is also
skeptical of the article about Dr. Rodger.

Don Rice, AC7ZB wrote, ''. . . the radiation belts have to be
heavily loaded due to an extremely large solar storm or a nuclear
detonation.  In either case, communications are going to be
disrupted whether or not somebody tries to 'remediate' the radiation
belts.  So the question is whether fooling with the radiation belts
will make a bad situation worse, not whether Dr. Strangelove is
going to push a button and turn off the ionosphere on a whim''.

''Scientists have been poking the ionosphere for many decades trying
to get it to do something, and short of setting off an ionospheric
nuclear explosion forty some years ago they haven't had much

''From the amateur radio standpoint, I think the greatest threat is
that hams will get cranked up and make statements that will get us
branded as a bunch of alarmist loonies.  That could be very damaging
to our efforts to curb BPL and other spectrum pollution''.

John Kelley, K4WY wrote (from his wireless pager), ''. . . space is
a big place, to shield the LEO birds with this technique would
require incredible energy levels over a global spectra of satellites
at varying orbits and ephemeris.  I think of the Northern lights as
an example of energy and ionized particles that at its peak can only
cover upper/mid latitudes.  Our current and near term future
technologies are still wrestling with IP in space environments,
autonomous control, investigating things like how to maintain a
human presence on the moon, so when taken in that perspective I
think we need a  reality check.  That said, every so often somebody
comes up with the ideas like beaming nuclear power back to earth and
other sci-fi ideas''.

If you would like to make a comment or have a tip for our readers,
email the author at,

For more information concerning radio propagation, see the ARRL
Technical Information Service at  For a detailed
explanation of the numbers used in this bulletin, see  An archive of past
propagation bulletins is at .

Sunspot numbers for August 10 through 16 were 37, 39, 27, 26, 45, 32
and 29 with a mean of 33.6. 10.7 cm flux was 80.3, 83.9, 84.7, 85.9,
86.4, 85.6, and 86, with a mean of 84.7. Estimated planetary A
indices were 5, 6, 8, 2, 4, 3 and 3 with a mean of 4.4. Estimated
mid-latitude A indices were 4, 3, 4, 2, 2, 2 and 2, with a mean of