Sunday, 19 September 2010

WSPR Stats with the "Runt Dipole"

I have now collected a week's worth of WSPR reception reports from the multi-mode beacon running with the new dedicated antenna, which I've named the "runt dipole".

The first night's operation suggested that the new antenna compares reasonably with the g5rv - but the week-long averages reveal a more complicated story...

Here's the average of the reception rates for the g5rv (in blue, as previously reported) and the new antenna (in red):

The performance of both antennae throughout the "Quiet Nights" average out similarly and the new antenna is pretty close to matching the rate at which emissions from the g5rv are spotted during the morning. However, the average performance with the new antenna is poorer in the evening - the spot rate is less than half that achieved with the g5rv.

The new "runt dipole" is - as its name suggests - nowhere near as effective a radiator as the g5rv, yet the overall reception rates are really quite reasonable. So what's going on?

I believe the answer lies in the directionality of the new antenna.

I explained previously that the g5rv lies approximately N-S, whereas the new antenna is close to NW-SE. I predicted that this would direct my beacon signals to a different set of potential receiving stations and this prediction is borne out by the reception reports.

If I look at the azimuth angle in all the reception reports and count them in angular
bins "around the compass" - effectively making a probability density estimate of reception rate against angle - the following results...

The very great majority of the reception reports associated with the g5rv were at an angle of 110 - 120 degrees from my QTH, taking the signal to Germany, Switzerland, Italy, etc. This is seen by the clear "lobe" in the g5rv data, above left.

In contrast, the reception reports associated with the new "runt dipole" are seen in the figure above right to be more uniformly distributed around the compass - the NW-SE orientation of the antenna gives better performance North and South, taking me to Spain (lots of spots from Javier, ea1jl), Iceland (the little spike pointing broadly NW shows how I reached Halldor, tf3hz) and into Scandinavia (solid, reliable propagation to Jon Ove, la3jj) as well as continuing propagation into Germany etc..

The ESE lobe in the g5rv data broadly pointing towards Germany is preserved in the "runt dipole" data - but I believe this is a reflection of the higher receiving station density (and, hence the increased probability of reception) in this direction, rather than anything to do with the radiation patterns of either antenna. This irregular location of the receiving stations is, of course, one of the charms(/frustrations) of WSPR!

All-in-all, I consider the "runt dipole" to be a success. It isn't up to the absolute performance of the g5rv (naturally), but its different orientation makes possible a satisfying range of beacon spots and succeeds in the original aim of freeing up the main station antenna. Not bad for a pair of inexpensive mono-band whips!

I'll be leaving the beacon running 24/7 and posting more stats/observations when there is something interesting to say.

...-.- de m0xpd

1 comment:

  1. Excellent comparisation. Would it be a idea to test also with a vertical? 73, Bas