[HamWAN PSDR] HamWAN over tideflats

[Matthew Lawson]

Its called tidal multipath. you are getting a reflected signal that is
causing cancellation or attenuation from the AP (source). take for example
a sign wave and mix it with another sign wave at the same frequency but
change the phase a little or a lot you will get addition or subtraction,
depending on the phase.  when the waves are 180 degrees* out of phase* they
will cancel each other, but as you shift phase they will attenuate or add
to each other. when both waves are *in phase* with each other you will have
a stronger signal. I am not a very good typist or writer, so I hope this
makes sense. I have in the past plotted (graphed) RSL vs tidal height for
microwave links over water. Its pretty neat to see the correlation of tide
versus RSL.

Another great example of multipath was when TV was analog you would get
ghosting. This is a great visual of multipath. As you receive a direct
signal at a given point in time you are also receiving the same signal at a
slightly delayed point in time. Thus a ghost image would appear due to the
time delay. You also used to be able see the picture flutter due to Doppler
shift mixed with multipath as an airplane would fly over at the right path.

Hope this helps in understanding on what going on.

73
Matthew Lawson
KC7EQO
442.100 Blyn Mt Repeater


On Tue, May 6, 2014 at 1:41 PM, Benjamin Krueger <ben.krueger at gmail.com>wrote:

> It would also be interesting to see two of these test setups, some
> reasonable distance apart, using one as the control and doing adjustments
> on the other.
>
> Tom, fwiw, I have all the same gear you do. We could set mine up for this
> kind of thing.
>
>
> On Tue, May 6, 2014 at 11:08 AM, Mike Culver <mculver at extencia.com> wrote:
>
>> So signal strength is clearly correlated to the moon :)
>> ________________________________________
>> From: PSDR <psdr-bounces at hamwan.org> on behalf of Tom Hayward <
>> esarfl at gmail.com>
>> Sent: Tuesday, May 6, 2014 10:59 AM
>> To: Puget Sound Data Ring
>> Subject: Re: [HamWAN PSDR] HamWAN over tideflats
>>
>> On Tue, May 6, 2014 at 10:53 AM, Bart Kus <me at bartk.us> wrote:
>> >
>> > That's a cool observation.  I would caution against equating
>> correlation with causation though.
>>
>> Agreed.
>>
>> > "The effect of tides on signal level" may indeed be an effect of
>> temperature changes (ducting?) or something else.
>>
>> Temperature didn't change much all day.
>>
>> > If I recall correctly, you were seeing very large (10dB?) high
>> frequency (1s period?) signal swings.
>>
>> Nope. I never saw more than 1 dB change during a 10 second period
>> (never really watched it for longer periods than that). The signal
>> very smoothly increased as the tide came in from the minimum to the
>> maximum I shared earlier. As it rose, I never saw it dip again by more
>> than 1 dB.
>>
>> > 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.
>>
>> Maybe I should try the same location with a MIMO modem.
>>
>> Tom KD7LXL
>>
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>
>
>
> --
> Benjamin
>
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