[HamWAN PSDR] HamWAN over tideflats

[Tom Hayward]

Last weekend I had the chance to play with my HamWAN portable setup
(this is the Poynting dish, RouterBoard Metal 5SHPn, 11.1V battery,
and tripod combo you see on http://hamwan.org/ homepage). I set up at
the Camano Island survey location shown on the map. It's right at
water level with a clear view toward Everett.

When I first set up, I got a signal level of about -58 dBm. Wow! This
is great for 21 miles at 5.9 GHz. As the tide went out, I saw the
signal dip to around -76 dBm. This was over about 250 yards of
mudflats. As the tide came back in, I saw the signal climb until the
water reached the bulkhead (about 5 ft from antenna), and the signal
level hit -54 dBm.

The computer model predicts a path loss of 145 dB, which would put my
signal level at -71 dBm. You can see from the numbers that the water
improves the signal level. This was not predicted. What causes it?

Kenny linked me to an interesting paper on the topic, although my
observations differed from theirs:
http://www.researchgate.net/publication/224138836_Slow_Frequency_Hopping_for_Mitigating_Tidal_Fading_on_Rural_Long_Distance_Over-Water_Wireless_Links

I find the effect of tides on signal level very intriguing. This is
the sort of effect that makes 5.9 GHz microwave interesting to me.

Tom KD7LXL