[HamWAN PSDR] dBm musings [was 8 ft horizontally = 9dB increase]

[Bart Kus]

Yeah, signal levels bounce around quite a lot.  I see swings much larger 
than 5dB on my link, and I attribute that to the trees I'm shooting through.

We did a few calibrated signal level measures once, from Cougar to a 
couple remote spots.  The levels did not match theory.  We didn't use 
the modems, but a proper sine wave signal source and spectrum analyzer 
on the receive.  To this day, I don't have an explanation for the 
deviation from theory.  It would be good to graph your signal levels and 
see if they're related to anything. Wind, traffic, temperature, time of 
day, etc.

If you wanna get really fancy, you can find a 2nd spot that's workable 
somewhere on your property, install a 2nd dish, replace the modem with a 
2-channel one, and start doing spatial diversity.  I don't think 
anyone's done that yet, although we have done polarity diversity.  You 
can log the signal strengths from each channel independently with such a 
setup, and see if there's some correlation over time.

Science!

--Bart


On 04/18/2014 03:19 PM, Dean Gibson AE7Q wrote:
> Prior details in the eMails below ...
>
> Shortly after the -75dBm report below, I started to see the value drop 
> to a usual range of -77-80dBm, with occasional excursions down to 
> -83dBm.  I spent three long sessions (one getting wet) out on the 
> roof, to no avail (I carry an Android tablet logged into the MikroTik 
> radio, to observe the effects of small adjustments). The variations 
> did not seem related to rain, although a wet antenna seems to drop the 
> signal about 2dB.  Interestingly, during the night there was little 
> change, but the commute hours seemed to generate the most 
> fluctuations.  I think that's because the line-of-sight path runs 
> about 20ft above 132nd St SE, a busy street connecting I-5 and Highway 
> 9 at the north end of Mill Creek.  Perhaps the signal is bouncing off 
> of vehicles?
>
> I originally thought that perhaps the decrease from the initial -75dBm 
> to -78dBm was perhaps due to foliage growth (this is Spring, after 
> all).  However, in the last week I've seen a very slight increase 
> (1-2dB) in the average signal level, so I don't know what to make of 
> that.  Perhaps someone has been picking flowers, or Bart has been 
> climbing the SnoCo DEM antenna tower and making adjustments (just joking)?
>
> Anyway, the reason for this idle posting is just to record my 
> observations for others to consider.  I have thought of raising my 
> antenna a couple feet using a similar gutter mount.  I then considered 
> that would probably place the center-of-mass above the gutter, which 
> would make the whole thing unstable in a strong wind without a 3rd 
> attachment point.  What appears to be the lower "attachment point" in 
> the images, is in fact just contact bracing, with gravity providing a 
> constant contact.  That's nice when the whole thing is stable with 
> regard to pivoting around the gutter axis (as it is now), not so nice 
> otherwise.  Yes, I could weight the lower end down to lower the center 
> of mass, but right now the weight is enough to make hanging the thing 
> on the gutter difficult, when standing on a slanted roof ...
>
> -- Dean
>
> On 2014-03-29 08:09, Dean Gibson AE7Q wrote:
>> Antenna inside (-89dBm), to test the site:
>>
>> http://www.ae7q.com/misc/media/5.9GHz-1.jpg
>> http://www.ae7q.com/misc/media/5.9GHz-2.jpg
>>
>> Antenna just outside the window (-84dBm), from inside:
>>
>> http://www.ae7q.com/misc/media/5.9GHz-3.jpg
>> http://www.ae7q.com/misc/media/5.9GHz-4.jpg --  God left a gap in the 
>> (many) trees, right in the path to Paine field ...
>>
>>   ... and from outside ...
>>
>> http://www.ae7q.com/misc/media/5.9GHz-5.jpg -- frontal view
>> http://www.ae7q.com/misc/media/5.9GHz-6.jpg -- in the line of fire ...
>>
>> Move the antenna 8 feet east for a 9dB signal strength increase 
>> (-75dBm = three green lights (power/Ethernet + two signal "bars") ...
>>
>> http://www.ae7q.com/misc/media/5.9GHz-7.jpg -- frontal view
>> http://www.ae7q.com/misc/media/5.9GHz-8.jpg -- in the line of fire ...
>> http://www.ae7q.com/misc/media/5.9GHz-9.jpg -- side view
>>
>> The nice thing about the mounting, is that there is NO attachment to 
>> the house, which makes adjustment trivial (sliding the mounting hooks 
>> in the rain gutter).  Even the Ethernet cable goes through 
>> pre-existing screening in attic vents.  The whole thing can be 
>> removed from the house without a trace in 20 minutes (10 minutes, if 
>> one is young and agile, which I am neither). It's (reasonably) 
>> light-weight (another plus, for the same personal reasons).
>
>
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