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| Propagation predictions for the International Beacon Chain for the UK, May 2018. |
Previously I had been calculating the field strength of each beacon and then converting that to an S point level. It was pointed out that this isn't the best way and that calculating the signal strength in dBm and then converting it would be better.
They are based on 100W to a dipole at 10m - we know that the IBP chain use a Cushcraft R5 antenna.
I then hit the problem as to what antenna gain do you use. This may sound simplistic, but in fact it isn't as the actual gain off a dipole will depend upon its height, its orientation and the required take-off angle.
Now, the take-off angle will depend upon what ionospheric mode is dominant at that point in time. That is, is it one F-layer hop, two F-layer hops or a combination of E and F-layer hops.
After a lot of thought and discussion I settled on setting the gain at both ends at 0dBi, which appears to give reasonable results - setting it at 2.15dBi gave over-optimistic results
Anyway, attached is the plot of predictions for the beacon chain for May 2018. I'll check to see how accurate it is and adjust the input files accordingly. The ultimate goal is to the transfer these settings to other HF predictions.
If anyone wants to report on whether they find these accurate or not please let me know. They are median predictions, which means some days may be better, some days worse.
Just click on the chart to enlarge it.
My take as a regular 12m operator is that the predictions are unduly pessimistic.
ReplyDeleteAnother observation I would make, on both this and many other predictions, is to ask: is an 'S' metet reading meaningful for the digimode-using masses? Is a SNR 'cutoff' of 0dB that is depicted by others as not worth the bother, similarly just totally out of date? I genuinely applaud the attempts to predict propagation, but generally find it of little use, partly for the reasons identified above. 'Just operate!' is a good motto.
Hi, The RSGB Propagation Studies Committee are looking at a number of different options, from using the required SNR for CW and FT8, to looking at all modes. There is really no "one size fits all" approach, and I would encourage people to use VOACAP, Predtest or Proppy for their actual working conditions. Or, as you say, get on the bands!
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