Wednesday, April 30, 2008

WSPR - 160m spots analysis, or how to evaluate a station performance.

For a contester it is always interesting to know how good is the site he is using, what kind of handicap or bonus he has vs a direct competitor, or what is the real impact of an antenna improvement (ie adding more radials on a vertical). Everybody knows how difficult it is to base and antenna evaluation on a few subjective S-meter reports, affected by QSB. Providing a uniform and objective reporting system (Signal to Noise Ratio), WSPR is the ideal tool, capable of providing near to the dB accuracy when enough spots are averaged. Furthermore it allows to evaluate antenna and site, accross a full window from band opening to band closure, this function of the direction and distance.Following are a few examples. Above is the plot of the spots reported by DF1VB on 160m for F1VS and F6IRF stations. As usual all reports have been adjusted taking into account the TX-power (all reports are matched as if the TX was always 1W). Of course the distance being shorter for my station(896 vs 631 kms), it is quite normal to see such a difference. GI8HXY having provided a significative number of spots for F1VS and my station during two 160m recent nights, I repeated the experience. This time the distance difference is not that important, and in favour of F1VS, but the signal difference is slightly higher in my favour. This may be due to my house obstruction in DF1VB direction, while the path to GI8HXY is perfectly clear with just a 3 degrees horizon blocking due to the mountains (which has no effect on such a path on 160m). Of course there are many more parameters which may explain this offset (I don't even know what kind of antenna F1VS is using...)Looking at VE1VDM reports, the difference is this time minimal over time, but we see clearly the effect of the later sunrise at F1VS location. It would have been interesting to see earlier reports, but I was running too low power until 2:00 to get my signal decoded on VE1VDM side, and unfortunately Vern was not QRV last night.Back to GI8HXY reports, I plotted the most spotted 4 stations (data only for last night). On the above plots the SNR's are just corrected for power levels. Despite different data time-range, the difference between F1VS and my reports is still the same (about 6dB). OH3XR stoppped transmitting around 3:30, which explains the abrupt and early signal drop.On the above plot I have tried to correct the distance effect. For this I used VOACAP path-loss model as a function of the distance (the propagation mode being identical for the 4 stations: 1F2) and deducted a correction factor proportionnal to the distance from Transmitter to Receiver. It is amazing to see the performance of OH3XR station vs all others (to be honnest I did not remember who OH3XR was, when I did that... I just selected the 4 more spotted stations, and Marko was transmitting 500mW, so is signal level did not alert me before I plotted the above !).
I just looked at Google, and quickly found that OH3XR aka OH9XX is a famous topbander and contester and owner of an exceptionnal contest site. I have no idea what antenna Marko was using last night, but it is interesting, isn't it ?

1 comment:

Anonymous said...

Thanks for the nice work on antenna comparison.

I'm using a different method, which reduces the effects of rapid ionospheric changes by simultaneous transmitting and receiving.

Charles Preston