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| Figure 1 - Three Band Overlay Noise Monitoring |
Greg Ordy
My first round of monitoring took place in July, of 2003, which is my local summer. The 160 meter, 80 meter, and 40 meter results are presented on other pages. I monitored each band on successive weeks. Even though sunrise and sunset times are changing, it's interesting to overlay the three different bands on one graph.
Fig. 1 shows the noise level of the 160 meter, 80 meter, and 40 meter band on a single graph. Due to changes in the day length across the two week monitoring period it's difficult (without massaging the data) to overlay all three days, some only the first day of each period is shown.
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| Figure 1 - Three Band Overlay Noise Monitoring |
The general sense I got from looking at this data, and the data on the individual band pages, was that 80 meter and 160 meter noise tends to move between their day and night values in relatively rapid transitions. On 160 meters, the transition seem closely tied to actual sunrise and sunset times. On 80 meters, at least during this monitoring period, the noise level would sometimes rise in the middle of the day, which is a little unexpected. 40 meters did show a difference between day and night noise levels, but the transitions took much more time. It seemed as if the 160 meter band was like a square wave, moving quickly between day and night noise levels. As the frequency went up, the shape of the transition went from square wave to more like a sine wave. It took many hours to move between the day and night noise levels.
The noise level was also lower on 40 meters, averaging 10 to 15 dB lower than on 160 meters or 80 meters.
On all three bands, sunrise appeared to have more influence as compared to sunset. Sunrise really shut off the noise. In some cases, the noise ramped up to night levels across several hours before sunset. It seemed as if the quietest time of day was within a few hours of sunrise.
Finally, on 80 meters, the (average) noise level would bottom out during the day. This did not happen on 160 and 40 meters. In all cases, the radio was set to the same preamp position, preamp #2 (maximum gain). I realized that on 80 meters the antenna was an inverted vee with the apex at 50', and on 160 and 40 meters, the antenna was a vertical. I have no doubt that the radiation angle is much lower on 160 and 40 meters. The 80 meter vee is low enough to the ground that it will be largely shooting straight up (NVIS). Perhaps that has impacted the relative noise strength between the two antenna types.
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