[HamWAN PSDR] Updated antenna radiation pattern software + some more readings

[Bart Kus]

Hello,

So I've improved the radiation pattern software to automatically:

1) Normalize the graphs to 0dB
2) Rotate the peak amplitude to the 0 degree position
3) Find the -3dB power points and calculate beamwidth
4) Measure the -120 and +120 degree power levels (adjacent antenna 
interference angles)
5) Detect the angular measurement resolution
6) Generate R-code for graphing
7) Spit out all the numerical details that belong with the pretty picture

Using this wonderful new automation (so easy to do now!) I put the ARC 
Wireless "variable sector" "120 degree" antenna through its various 
settings.  The results are on the antenna's lab page:

https://www.hamwan.org/t/tiki-index.php?page=ARC+ARC-VS5818SD1&structure=HamWAN

The bogosity of "variable sector" is visible as the radiation pattern 
hardly budges between 60deg, 90deg and 120deg adjustment positions.  
This a fixed 60 degree sector antenna as far as I can tell.  If HamWAN 
was using 6-sector cells it would be perfect.

Next I re-ran the measurements on the Laird, with the results updated on 
the antenna's lab page:

https://www.hamwan.org/t/tiki-index.php?page=Laird+SAH58-120-16-WB&structure=HamWAN

Pretty good show, just like last time.  A calculated 3dB beamwidth of 
111 degrees is a lot closer to the 120 deg spec than the ARC Wireless.  
The +/- 120 deg rejection though could be nasty in real life.  Gotta 
check it out without all these echoes.

One obvious thing is that the graph isn't centered correctly.  This is 
because the centering/rotation algorithm aligns the 0 deg mark with the 
maximum signal reading over the whole pass.  In this case, that was an 
off-center lobe on the front face of the antenna.  I need to re-work the 
auto-centering so that it uses the -3dB points instead and centers right 
in the middle of them.  But tomorrow, too tired tonight.

In short, the sector antenna story is sucking.  We need good + cheap 
sector antennas for this thing to work!  The Laird is $180/ea with 
questionable +/- 120 deg rejection.

--Bart