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[Ham-80211] OT??? High power 2.4 GHz rules change

Tim Gorman ab0wr at ab0wr.net
Sun May 21 00:35:07 UTC 2006


See my comments below.

On Saturday 20 May 2006 16:35, doc wrote:
>  > Tim Gorman wrote:
> >
> > Point 2: 1 watt at 2.4Ghz is plenty of power to work all the way to the
> > radio horizon for most installations. Raising power levels to blast
> > through obstructions is NOT a good way of doing things, it shows poor
> > engineering judgment. Finding better paths and setting up mesh networks
> > that will allow routing around obstructions is a much better answer for
> > almost all system metrics - initial cost, operating cost, spectrum
> > pollution, etc.
>
> I have to question the assumption underlying this
> statement.
>
> Much higher power than 1W will be necessary to maintain
> solid communications for the following circumstances:
>
> 1.  Airborne obstructions, e.g. rain, snow, hail, sleet,
> smoke, heavy mist, windblown dust, windblown pollen, etc.
> (your airborne nuisance will depend on your QTH -- expect
> more if you deploy in disaster-impacted locales)

Why do you think higher power will be needed? Exactly what radio horizon 
distances do you think you will be trying to cover with typical 
installations? Especially in disaster-impacted locales? Most of the links you 
will find in disaster-impacted locales will be local networks or 
point-to-point links - neither of which require high power *ESPECIALLY* on 
the amateur bands. 

If you think you will be setting up a 2.4Ghz SS hub with an omnidirectional 
pattern covering a radio horizon of 25-40 miles then I can understand the 
statement that you will need higher power - but so will all the stations 
trying to connect to you. That means they will interfere with each other AND 
with you and will just make an unholy mess of the spectrum being used. Its an 
issue you just can't get away from - its the nature of the beast.

And while you are doing all this just how many people are you going to piss 
off that are running Part 15 networks? That's all the amateur radio community 
needs - a big black eye, especially if it occurs during an emergency.

>
> 2.  Antenna inefficiencies, e.g. snow or ice on the antenna,
> the impact of various environmental sources such as acid
> rain, soot, salt-containing rain or mist, etc., slight
> misalignment due to unusual winds, etc.

Would anyone like to put forth the word that applies here? Hint: begins with 
the letter "r".

If you are using antennas that become misaligned enough to cause a problem 
with a link due to unusual winds then that tells me you are using high-gain 
antennas to begin with - which don't need the high power during regular 
operation. So when you are saying you don't want to have to run APC you are 
also saying that you will just run the link ALL THE TIME at the power level 
needed to overcome any possible impairment - whether the impairment exists or 
not.

This is an even worse engineering practice than raising power levels to blast 
through an existing obstruction - you are just going to blast the signal out 
whether you need to or not. 


>
> 3.  Seasonal changes, e.g. leaves not there when tests
> were conducted show up in Spring, or new growth as a result
> of taller bushes/trees, etc.

I've been there when system designers haven't considered all the environmental 
conditions, especially with 11Ghz systems. Again, just blasting away with 
higher power is a poor engineering fix. 

>
> Yes, there are reasons for the availability of higher-
> than-1W power levels and they may be more rather than
> less frequent.

I'll repeat, use of high power with spread spectrum is self-defeating in the 
extreme, especially when the spectrum space is limited. If all you ever 
expect to have is one or two stations in any 25 mile radius using SS under 
Part 97 then have at it with your high power. If you ever expect to grow past 
that point, i.e. three or more stations, then you need to understand what use 
of more than the absolute minimum power needed does to the spectrum capacity.

>
> One key question goes to the mission-critical nature
> of making and holding the link and the capacity to
> locate multiple versus one-to-one sites.

Those multiple stations have to be able to communicate or they are worthless. 
The higher power they run the more they interfere with each other. It's why 
the cell phone people don't just increase their cell site power in order to 
increase capacity (i.e. they can reach further distances and cover more 
people). They actually lower the cell site power and put more cell sites in. 


>
> IMHO, when one absolutely positively has to make and
> hold the contact and cannot count on multiple link
> sites then one needs QRO.  The regs nor the spectrum
> planning cannot preclude QRO or it makes the band
> unreliable for mission critical apps.

The regulations don't preclude QRO, especially for emergency situations. But 
whoever is running that QRO also needs to understand all the ramifications - 
such as the liklihood of interfering with the local Part 15 network the 
American Red Cross has set up in their shelter to link PC's doing H&W work or 
inventory work, etc. 

tim ab0wr






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