[Lowfer] W7IUV in EN90xn

[N1BUG]

I think I know that headache. I have spent two winters trying to 
understand what drives trans-Atlantic propagation variation. Some 
say it is primarily geomagnetic activity. I agree that often appears 
to influence propagation changes, but...

Conditions often peak just prior to onset of a disturbance. I have 
observed no clear evidence that this is related to the length of the 
preceding calm, i. e. that it is simply the result of prolonged quiet.

When a disturbance hits, one of the following is likely. I have seen 
each of them more than once.

* Immediate depression of TA propagation

* Initial enhancement of TA propagation followed by depression

* No apparent affect

* One of the above with near immediate rebound after the disturbance 
subsides

* One of the above taking several days to recover

* One of the above but propagation continues to decline for up to 
several days after the disturbance subsides

Sometimes propagation goes from very good to very poor and vice 
versa during quiet conditions with no apparent precipitating factor.

So what really drives variation in TA propagation at 2200 meters? 
Darned if I know!

I have noted some interesting things with longwave broadcast 
reception as well.

There are nights when all TA LW BC paths are good, but these nights 
are few and far between.

There are nights when the highest latitude path (Iceland) and the 
lowest latitude path (Morocco) are very good but everything in 
between is weak or nonexistent. This, in fact, is a very common pattern.

There are nights when neither the highest nor lowest latitude path 
are working but those in between are good.

There are nights when either the highest or lowest latitude path is 
working along with those in between, but the other extreme is not there.

There are nights when only the lowest latitude path is good. These 
do tend to occur during or just after geomagnetic disturbances.

There are nights (common) when one or two stations are in very well 
while all others are weak.

Given two years of observing 2200 meters, LW BC and the utility 
stations DCF49, HGA22, and DCF39 I have a theory that propagation is 
just very spotty. There are times that one specific location is 
strongly favored. There are times when a few or several locations 
are favored; the pattern varies. There are times (rare) when all 
locations seem to be favored. There are times when no locations seem 
to be favored (does this mean there is no TA propagation or only 
that it is favoring some location which lacks a transmitting station?)

What have I learned from two years of observation? Only this: LF 
trans-Atlantic propagation is highly variable with seemingly complex 
patterns which are not at all understood by me.

Paul N1BUG




On 03/07/2018 05:59 PM, Larry Molitor via Lowfer wrote:
> When you come right down to it, it's kinda ridiculous to try to compare stations that are more than a mile or two apart.
> Ignoring propagation for a moment, the signal level at a distant point is more dependent on far field ground and "take off angle" (which is dependent on both antenna design and far field ground) than it is on EIRP.
> I have personally seen signal strength differences as much as 20 dB between nearly identical stations a few miles apart  where the only difference was the dirt within 20-30 wavelengths from the antenna.
> Ignoring the dirt for a moment, the differences between a "low latitude" path (Ward to Mike) and  high latitude path (Larry to Mike) are not only huge but completely unpredictable. The hi-lat path between Larry and Mike is through the Auroral Influence Zone. Mostly this means a  lot more attenuation than a more southerly path but it can also mean more "spotlight prop".
> When you combine both of the above, there are too many variables in the equation for me to be comfortable making any conclusions.
> Now having said all that, I am a novice when it comes to 137 kHz prop. It seems to , more or less, follow most of the rules I've come to accept for 160m and even 630m. But the "more or less" part is admittedly giving me a lot of trouble. After a couple years of watching Ron and Ward, I can pretty much predict the path between WA and AZ. But the path from here to the east side is giving me a headache.
> Better, I think, to just note the results and be happy rather than try to analyze it!
> Larry - W7IUV