[PPRAANet] Propagation 1/7/05

[W0rw at aol.com]

Paul  NA5N makes propagation simple...
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Gang,

For those of you who haven't been keeping up with current events,

we are no longer in the active sun :-)  Remember 2 years ago when we

were running solar fluxes skirting 200?  And 10M was open?  And 20M

was there 24/7?  Those days are over. 


This post will address the crummy current conditions, and also an

overall look at propagation with our solar fluxes less than 100 and

this time of the year, particularly for those new to the list. 


On January 4-5 UTC, inspite of the so-called "quiet sun," there were two

solar flares. Small by the standards in the past few years, only a

C2 and a C8.  But, they came from a sunspot region that was almost in

the center of the sun, such that all the hot plasma gasses and electrons

hurled out by the flare was directed at earth. Had the flares occured

near one of the limbs (edges) of the sun, things would have been hurled

out into the solar system away from the earth. Of course, when this

solar mass is ejected into space it's called a Coronal Mass Ejection, or

CME.  It takes several days for the shockwave of the CME to hit earth,

which it did today (Friday) this afternoon. As the shockwave hit earth,

it compressed our magnetic field and triggered a geomagnetic storm.

Also, the magnetic orientation of the CME shockwave was such that it

caused some of the magnetic field lines to point southward. This is

what really fuels a geomagnetic storm. If you look at the space data

on the NOAA site, this is indicated by the negative Bz (-Bz) term. 


There will be enhanced auroral activity this evening for our friends

in the northern latitudes. 


As a result, we are now in a MAJOR GEOMAGNETIC STORM running K=6

(out of K1 to K9). NOAA has also issued a K=7 or greater alert for

7 Jan. 2300 (like now) to 8 Jan 0800 (after midnite friday). 


That means that tonight conditions will be pretty cruddy. Very noisy

and HF signals will be highly attenuated, gobbling up QRP signals pretty

fast. The A-index is expected to be 40+. Tomorrow midday and beyond,

conditions should return to normal. 


Solar activity is very low with the solar flux only being 84. This is

insufficient to highly ionize the E and F layers during daylight hours,

lowering the MUF to barely above 20M during the day. Recent midday MUF's

are running about 15 MHz.  Bouncing a signal off the E/F layers with a

good angle (longer the better) will extend the realizable MUF a bit, to

about 18 MHz or so. 


If you look at a map showing the MUF, you will notice the contour lines

run almost north and south, or northwest to eastwest. This means if you

are working 18 MHz when the MUF is dropping, the band can go out very

quickly as the contour lines to lower MUF's travels from east to west.

It will go right over your heads in minutes.  The same is true later in

the evening when 20M drops out. It will die quickly - like in the middle

of a QSO. This condition also causes strong QSB. 


Right now, the Critical F2 frequency during daylight hours is only

7-9 MHz. This means if you squirt a signal straight up, 9 MHz will be

bounced back at you, while 10 MHz will pass right through the ionosphere

into space. However, most of us use an antenna system that does not send

signals straight up, but off at an angle. The MUF will be higher as a

function of the take-off angle of your antenna. 


A few pointers for the quiet-sun Winter propagation: 


FOR DAYLIGHT HOURS, you want an antenna with a low takeoff angle to

extend the MUF above the critical F2 frequency. This means a vertical

antenna. If you want to work DX on 20M, or whatever is open higher than

that DURING THE DAY, use a vertical for the low takeoff angle for the

longer skip paths and get your signal to bounce back well above the

critical F2 frequency. 


FOR EVENING HOURS, you want to use a dipole antenna with a higher

takeoff angle. In this case, you are not trying to extend the MUF, I

mean 20M is dead anyway, right? You're pretty well limited to 30M, 40M

or 80M. What you ARE trying to do is get your QRP signals through our

atmosphere (you know, clouds, rain, snow, cold dense air) as quickly as

possible. In fact, straight up ain't a bad idea right now at night :-)

The higher takeoff angle will allow your signals to bounce back to earth

closer to you, working nearby states.  Low take off signals means your

bounce will fall out in the Atlantic or Pacific Ocean on 40M ... well,

at least a long ways away. While that may be DX, the longer your signal

path, the more of it is getting gobbled up.  So right now at night, the

trick is to get your signals up to the E layer and back to earth in a

relatively short path, which means a shorter ABSORPTION path too. You'll

be working stations closer, but at least your QRP signals will have the

least attenuation for a more enjoyable QSO. 


I'm not an antenna guru and I know some people think vertical antennas

are a joke and worthless (never mind that most commercial broadcast

stations use them! Must be a reason).  But I will tell you, I believe a

good, modest home QRP station is one with a dipole AND a vertical antenna

system that you can easily switch between. There are times when the

characteristics of the low takeoff angle of a vertical will clearly

outperform your dipole. And, for the night time reasons given above,

there are times when the dipole will be the better antenna. 


For those of you with both a horizontal dipole and vertical, what are

your experiences right now between daylight and nighttime operating

with both antennas?  Or, if you've never given it much thought, hopefully

the above will inspire you to do a little playing around and see for

yourself. 


Sorry about the conditions right now into early tomorrow (saturday), but

beyond that, it should be a good weekend for QRPing on the air.

Have a great weekend. 


72, Paul NA5N 


via w0rw