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

Tim Gorman ab0wr at ab0wr.net
Sat May 20 10:33:52 UTC 2006


Guys, this is a philosophy issue as much as a technical issue.

Point 1: experimentation typically is not done at high power levels. You get 
things working at close distances using low power and then scale up, not the 
other way around. That means that using experimentation as an excuse for 
removing APC control is basically a non sequitur. 

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. 

Point 3: APC controls using 802.11h is not just for big companies. The 
routines are built into alternative firmware loads for wireless routers. Use 
DDWRT with the Linksys series of routers and you have it built-in and 
available. 

Point 4: Narrow band signals co-exist by not stepping on each other. They can 
do so by not occupying the same spectrum at the same time. Spread spectrum 
does not have that option. Spectrum sharing for SS operations, and that 
includes OFDM whether the FCC includes it as SS or not, *MUST* be done by 
using control of power levels to avoid interfering with other users on the 
same spectrum as well as with narrow band operations in the same spectrum. 

You mention Pactor3 on HF - this is a prime example of a mode that does NOT 
typically follow this philosophy and catches heat for the interference it 
causes other operators in *every* discussion forum where it is discussed. 
While mt63 does not cause as much interference that can probably be 
attributed to the relative un-use of the mode as to anything inherent in the 
mode itself.  

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

While I agree with you that less regulation is better, regulations which set 
expectations for what is good engineering practice are not onerous, they only 
serve to set levels of expectations. The APC regulation does this. 

If it didn't exist how many hams would be tempted to just buy amplifier bricks 
to hook up to their wifi routers and go on down the road without ever 
thinking through the ramifications? There is no "experimentation" in this - 
other than in seeing what kind of obstructions you can overcome with high 
power.

Even the ARRL recognizes the need for APC - they just throw out the claim that 
operators can manually control their power better than a built-in feedback 
loop can. If you want to talk about a "Practical Impossibility" - talk about 
how *this* will be done. How many SS systems even have an audio output for 
the SS signal itself for the manual operator to listen to? And do you know 
any human who can tell the bit error rate of a SS signal by listening to the 
signal through a speaker? 

My philosophy on this - FWIW.

tim ab0wr

On Friday 19 May 2006 19:28, Jeff King wrote:
> On Fri, 19 May 2006 17:38:27 -0500, Tim Gorman wrote:
> >OFDM, if the frequency span occupied is much, much greater than the
> >modulating bandwidth, will probably also be considered spread
> >spectrum based on my reading of the FCC rules and regulations under
> >CFR 47.
>
> Nope. While OFDM may appear spectrally as "spread spectrum like", it is
> not. This is exactly why when the first 802.11a products came out, the
> makers had to get a wavier from the FCC for Part 15. Then they came out
> with the DTC rules, which addressed spectral density and allowed this
> emission types to run the same power levels as traditional spread spectrum
> part 15 devices. Also, Pactor3 and MT63 are popular HF modes, and are OFDM
> modes.
>
> >802.11h has been specifically designed to work in conjunction with
> >802.11a (an OFDM system) to provide APC functions. And it works! So
> >saying that it is a "Practical Impossibility" has already been
> >proved wrong.
>
> For a large company. I think the ARRL was referring to some Joe working in
> his shack. Don't forget that one of the basis and purposes of ham radio is
> experimentation, and the fewer rules that get in the way of this, generally
> the better. I am in support of the removal of the APC rule just as I am
> against the HF regulation by bandwidth giveback. The fewer rules we have,
> the better.
>
>
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