[plug] OT: Point to multipoint wireless

[Denis Brown]

At 09:27 12/03/2004 +0800, Kai Jones wrote:
>Bernd Felsche wrote:
>>On Thursday 11 March 2004 16:27, Kai Jones wrote:
>>
>>>Distance from Family Day Care to the Rec Centre is about 150m so

<snip>

>>>I just had a look at that URL and the hardware they're using looks 
>>>familiar. I wasn't sure if I could use RG-213, Beldon or some other 
>>>lower-loss coax cable but it looks like they've used that, with N-type 
>>>PL-259 connectors, so that's no problem. If that is a PL-259 I can see, 
>>>they would've used N-type instead of standard PL-259 to try and avoid 
>>>coupling losses because when you're dealing with frequencies in the GHz 
>>>range antenna coupling's are usually a signifacant portion of a 
>>>wavelength, which causes the coupler to radiate signal instead of the 
>>>antenna radiating the signal.

And there's RG213 and RG213 IIRC...

Many years ago I worked in airborne geophysics.   We used Collins VME gear 
(radio altimeter) and the avionics fellow (in South Africa at that time) 
could not get RG213A I think it was -- double screened, next week's Lotto 
numbers, top-of-the-line stuff.   Instead he used RG213B, single 
screened.   Ran the Tx and Rx feeds in parallel in the fuselage until they 
parted company at the wing level - Tx dish on one wing, Rx on 
other.   Worked fine until we reached about 100ft above ground level and 
then the coupling took over (between the cables in the fuselage) and the 
altimeter suddenly indicated NEGATIVE altitude.

I learned that pilots are very sensitive people, about altitude!

Might not be a factor for you since there is probably only one feed but may 
be significant if there are other interference-causing gigahertz sources 
close by.

Cheers,
Denis