Wednesday, April 30, 2008
WSPR: Evaluation of two160m RX-antennas using WSPR reports
The following examples focus on the 160m band, where the WSPR activity is increasing. Last night more than 30 stations were active on the band, which was in excellent shape, with very low level of statics. The EU map show the active stations between 21 and 22z, while the map covering EU and USA show the active stations between 2:30 and 3:30Z. Using the automatic antenna switching described in the previous posts, I took this opportunity to try to evaluate the performance of my two RX antennas. Although the number of spots considered is somewhat limited it already gives interesting indications. For the following plots, all reports have been normalized to 1W (deducting/adding the corresponding dB's when more or less power was used).The above graph shows the performance of my RX magnetic loop (in red) vs my K9AY (in blue) for a 850 kms circuit. Both antennas are pointing north (direction where my power line noise is minimal). Both antennas have a broad pattern, with a min E/W for the loop, and a min to South for the K9AY. For this direction/distance the magnetic loop is about 2dB better than the K9AY.As shown on the above, increasing the distance, tends to reduce the difference (the above plot is for a 2000 kms path) . Due to the limited number of spots from USA (especially on the loop), the plot would be meaningless, but it seems that the K9AY is working better at a longer distance, as more than 2/3 of the US spots were obtained using the K9AY. Will come back, on this when enough data is available. The above graph, shows the directivity of the loop, as F1VS is moreless located on the deep of the loop pattern and at a distance of 450kms. I was wondering if the directivity of the loop was still good for signals arriving quite high above the horizon... the answer is obviouly yes! (the K9AY has about 3dB front to side), in this direction the K9AY is obviously better (btw I have no idea how to explain the sinusoidal shape of the loop curve... but considering the limited number of spots, it may just be a random effect...). Those results are obviously only valid for my location, where my main problem is to eliminate the noise generated by the very High Voltage power line... The moon before moonset. The line is running East-West and located in my South. On 160m, the minimum noise is obtained with the magnetic-loop perpendicular to the power line (N/S). The noise floor increases by some 10dB when the loop is oriented E/W.