Sunspots and Propagation on "Low Bands"

[KX5JT]

Here comes another "newbie" question.  I am guessing it belongs here.  I'm seeking a discourse from the more experienced and knowledgeable concerning what low sunspots mean for AM.  I understand more sunspots helps DX on higher bands.  I thought I read somewhere that indeed the opposite may hold true for the low bands.  I know *most* AM operation (except when 10m or higher is actually open) occurs on 160, 80 and 40, the so-called "Low Bands".

I think I understand there is a relationship between number of sunspots and the MUF for propagation.  Doesn't the MUF rarely come down below 40 meter even with no sunspots?  Does a higher MUF indicated stronger overall propagation on the Low Bands, which may include the static and noise floor levels too? 

What does it all mean for us AMers?  I seem to see some people in the forums (and other places) hope for more sunspots and others hope for the quieter conditions of less sunspots.  This confuses me a little bit. 

John KX5JT

[KA1ZGC]

Angle of ionospheric refraction is the key here, that is to say the angle relative to the horizon where you get the most refraction at a given frequency. That angle gets lower as you increase in frequency, and higher as you decrease in frequency.

The relationship between frequency and refraction angle is determined by sunspot levels. The higher the sunspot levels, the higher the refraction angle at a given frequency.

When sunspot activity is high, the higher bands are open at low angles, meaning long skip zones and good DX, while the lower bands are open at high angles, meaning good consistent coverage for hundreds of miles with no skip zones.

This of course varies according to time of day, but when sunspots are high, 75 and 160 are very reliable regional bands.

When sunspot activity is low, the higher bands may not open at all, and the lower bands are opening to more medium- and low-angle paths. These days you can work coast-to-coast on 75 meters on a quiet night. The downside is that skip zones now form because the angles are so low.

What people are lamenting is a lack of skip zones forming on 75 and 160. The levels are so low that 75 and 160 are behaving somewhat like 20 and 40 do during a sunspot high.

It's harder to work the locals at night on the lower bands these days, which is why you hear a lot of pining for higher sunspot numbers.

[Steve - WB3HUZ]

Conditions on 80 and 40 lately are mostly driven by less D layer absorbtion and the F layer being generally higher (thus the lower angles you mentioned Thom). Sunspot activity has little or no effect on 160 as the D-layer is driven by sources other than the sun once the SSN drops below 80-100.

The thing is that these same "conditions" exist on 80 and 40 even when the SSN is much higher. Most people don't know it because you need a good low-angle antenna to take advantage of them.

[K1JJ]

Yes, the "optimum" take-off angle for a given time is the key.  Like a boiling mass of turdlets, the ionosphere is always changing and matching your antenna to this "optimum"  refraction angle can be a task.  There is usually a best range of TO angles for a given time of day, sunspot activity and frequency.

A number of years ago an antenna guru told me an interesting relationship.... once you find the optimum TO angle for a given frequency, just double the freq and halve the TO angle to find the next one.

For example, we will use some real world numbers and assume the bands are open from 10M-75M:

If the optimum take-off angle from east coast USA to Europe on 3.8 mhz is about 40 degrees, then the optimum angle on 40M will be about 20 degrees, and the optimum TO angle on 20M will be about 10 degrees  and 10M will be about 5 degrees. It will vary from this of course, but this is a good guideline for DXing. I believe this relationship breaks down on 160M because of the Geo-HuzMan disco duck effect.  Optimum angles for 160 to Eur are probably down around 20 degrees, considering how well the verticals do there.

I find this generally to be the case and have designed my antenna systems to reflect this relationship. It's fortunate it works this way, cuz we naturally can vertically stack antennas at a  higher wavelength above ground as the freq increases, giving us this lower angle.   God thinks ahead for us puny humans sometimes...


T

[KA1ZGC]

The thing is that these same "conditions" exist on 80 and 40 even when the SSN is much higher. Most people don't know it because you need a good low-angle antenna to take advantage of them.

Absolutely, and it's the ones who don't have good low-angle ants that are mostly lamenting the skip zones forming on 75 at night these days. Pretty much "game over" for them when that happens.

[KB2WIG]

"  If the optimum take-off angle from east coast USA to Europe on 3.8 mhz is about 40 degrees, then the optimum angle on 40M will be about 20 degrees, and the optimum TO angle on 20M will be about 10 degrees  and 10M will be about 5 degrees. It will vary from this of course, but this is a good guideline for DXing. I believe this relationship breaks down on 160M because of the Geo-HuzMan disco duck effect.  Optimum angles for 160 to Eur are probably down around 20 degrees, considering how well the verticals do there. "

[DD - Donald Duck voice]
[BS - background singers]
[EP - Elvis voice]

All of a sudden I began to change
I was on the dance floor acting strange
Flapping my arms I began to cluck
Look at me..
I'm the disco duck

[DD:] Ah, get down, mama
I've got to have me a woman, ha, ha, ha, ha, ha
[BS:] Disco, disco duck
[DD:] Got to have me a woman
[BS:] Disco, disco duck
[DD:] Oh, get down, mama
[BS:] Try your luck, don't be a cluck, disco
[DD:] Disco
[BS:] Disco
[DD:] Disco
[BS:] Disco
[DD+BS] Disco
[BS:] Disco, disco duck
[DD:] All right
[BS:] Disco, disco duck
[DD:] Ah, get down mama,
Oh mama, shake your tail feather, ha, ha, ha, ha, ha 

Tom Vu, I blame you for this memory. It has been awakened. Disco sucks. I hope you are happy with this.


klc

[Steve - WB3HUZ]

Or head to 160.

The thing is that these same "conditions" exist on 80 and 40 even when the SSN is much higher. Most people don't know it because you need a good low-angle antenna to take advantage of them.

Absolutely, and it's the ones who don't have good low-angle ants that are mostly lamenting the skip zones forming on 75 at night these days. Pretty much "game over" for them when that happens.

[K1JJ]

Tom Vu, I blame you for this memory. It has been awakened. Disco sucks. I hope you are happy with this.

hehehehe  Ya never know what will trigger deep dark memories.

Actually I really liked the disco era. It was the best chick hustling time in history.

Before that, in the late 60's and early 70's during the hippie/freak era, most of us sat on our asses and listened to bands and singers. It wasn't cool to go around the crowd hustling chicks cuz we were supposed to act like farmers... :-)  Elvis and hustling was out.

But when Disco dancing came in the first few years, all hell broke loose and it was a free for all. Babes everywhere all dressed up in those tight pants. Then came disco roller skating - wow. You could check the babes out really well, skate-dance with them and go home with five phone numbers a night ready for future action.  Yep, disco was my favorite time - a good 7 years or so.  When punk rock took over next, and it was gone... sigh.

T 

[w4bfs]

Tom Vu said " like a boiling mass of turdlets " .... goes far to explain shitty conditions ...73...John