[HamWAN PSDR] Sector self-interference rough results

[Bart Kus]

Hello,

I setup 2 similar sectors (in terms of their +/- 120 deg attenuation 
characteristics) on a section of Rohn 25, angled at 120 deg away from 
each other.  The Laird and the 19dBi Ubiquiti were the specific sectors 
used.  I was able to measure the path loss between them as -65dB.  This 
seems pretty good!  But maybe it's not enough.  With +31dBm @ full power 
on one sector, 65dB of attenuation results in -34dBm out-of-band power 
at the adjacent receiver.  The attenuation of this remaining -34dBm is 
left up to the receiver filter skirts. By transmitting low-power in-band 
packets into this same receiver, a throughput slow-down was observed.

Shifting the interfering RF 30MHz further away from the channel being 
measured paradoxically resulted in a FURTHER slow-down.  This is not 
consistent with filter skirt behavior.  Something else must be at play.

These are pretty rough results, since the setup is entirely in my garage 
and is subject to tight confinement which means lots of reflections.

I need to test the path loss when the sectors are spaced further apart, 
to simulate a larger tower structure, or the presence of an intentional 
separation system.  In a real-world deploy the sectors may also be 
staggered vertically to minimize coupling.

I should also try building shields to see if that improves isolation.  
As Rob pointed out, gotta be really careful about destructive 
interference bouncing off these shields.  Which means measuring FR over 
several angles.  Good thing a 2-axis positioning rig is on the way to 
facilitate this kind of testing.  :)

RF is hard.

--Bart