Topband: 160-Meter propagation

[k9la at frontier.com]

Topbander enthusiasts,

On Dec 5 Brian VE7JKZ asked about solar flux in relation to 160-Meter propagation and wondered about solar min versus solar max.

On Dec 6 Bob W7RH wondered if anyone has looked at space weather data with respect to propagation during ARRL 160.

Also on Dec 6, George W8UVZ commented that the band isn't as poor as some would suggest.

Those are three interesting comments, and they indicate that we struggle to understand propagation on 160-Meters, especially on a day-to-day basis. Propagation on 160-Meters is absorption-driven, meaning we usually don't have to worry about MUF as it is usually high enough to get a signal from A to B. The real problem is our lack of understanding of what's going on down in the lower E region (where absorption occurs at night since the D region is for all intents and purposes out of the picture for 160-Meter considerations).

Efforts to correlate space weather (solar flux and K index) to the day-to-day propagation on 160-Meters usually don't give good results, as there's an important variable that's left out – events in the lower atmosphere coupling up to the ionosphere. This appears to play a big part in what's going on in the lower E region, but we have no parameter to measure this effect. Perhaps we will in the future, as scientists are developing physical models of the ionosphere (for example, GAIM out of Utah State University, which stands for Global Assimilation of Ionospheric Measurements) and they'll have to address this. Indeed, we're seeing more and more attention in the scientific literature paid to events in the lower atmosphere and how they affect the ionosphere.

With respect to solar min versus solar max, the old adage that 160-Meters is best at solar min is somewhat of a self-fulfilling prophecy. We've heard 160 is worse at solar maximum, so we don't get on much then. Anyway it's easier to work the world on 10-Meters with S9 signals at solar max rather than signals at our noise level on 160. If you dig into the physics of the nighttime ionosphere at solar min and solar max, you won't find a huge difference. In my opinion, based on this and on log data by those who hang around on 160 during solar max, there's lots of DX to be worked at solar max, too. I remember W8JI worked over 200 countries and all 40 zones at solar max of Cycle 23 around 2000. Sure, he's got a great station and locale, but much of that effort was just being there day after day.

In summary, I don't think we can predict propagation on 160 (interestingly, we can't precisely predict it on a day-to-day basis on HF, either). Also I don't think solar max on 160 is as bad as we think. And with signals near our noise level, small changes in the ionosphere in key places will contribute to some people saying 160 was wonderful last night while others will say we didn't hear a thing.

For discussions of many of these issues, visit http://myplace.frontier.com/~k9la.

Carl K9LA