Tuesday, October 21, 2008

VOACAP reliability, the end of the myth ? part2

Following are a few more plots concerning the F to ZL2 path. The above plot shows the signal levels reported by ZL2TLD over a longer period than the earlier published one. You can see that the delta between the lower and higher reported levels, is around 10dB, which can be explained by day to day propagation variation, but also by some punctual intereferences (we are not alone on this part of the band). The long path "average" is around -22dB for 1W TX power in a -1dBi gain antenna (simulated gain of my vertical at 10degrees). The short path average, under the same conditions, is some 2.5dB higher. Now here are the VOACAP simulations for the short and long path. This time I used method 30, CCIR monthly coefficients (and NOAA monthly SSN smoothed indexes). I used "isotropic antennas" (both antennas have negative gain at considered 10degrees angle) and switched the multipath "off". I used -150dBW/Hz noise level at 3Mhz (5dB quieter than the average recommended -145dBW), and pushed the required SNR to 12dB (-22dB observed +34dB for BW relation). The result is about the same... 50dB are missing to make the link possible...

Above is the short path... about 40dB are still missing to match the observed -20dB average level in 2500Hz, to the VOACAP simulation (forgetting that both antennas have negative gain, when compared to the isotropic used in the models.)
It is not all, but of course I kept the best for the end... stay tuned !!!

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