[HamWAN PSDR] HamWAN over tideflats

[Bart Kus]

That's a cool observation.  I would caution against equating correlation 
with causation though.  "The effect of tides on signal level" may indeed 
be an effect of temperature changes (ducting?) or something else.  If I 
recall correctly, you were seeing very large (10dB?) high frequency (1s 
period?) signal swings.  It'd be fun to understand that phenomenon as 
well as the slower one you're reporting here.  Perhaps you were just 
being slowly moved through an interference node with the water level, 
and an antenna mounted +/- 2ft from your antenna's elevation might have 
reported the opposite power behavior?  I also wonder if there is any 
polarization rotation happening here.

--Bart


On 5/6/2014 9:05 AM, Tom Hayward wrote:
> 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
>
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