From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp121.iad3a.emailsrvr.com (smtp121.iad3a.emailsrvr.com [173.203.187.121]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id F385821F338 for ; Sun, 21 Dec 2014 08:45:55 -0800 (PST) Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp8.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 67CDF380115; Sun, 21 Dec 2014 11:45:54 -0500 (EST) X-Virus-Scanned: OK Received: by smtp8.relay.iad3a.emailsrvr.com (Authenticated sender: dpreed-AT-reed.com) with ESMTPSA id B92B23800BD; Sun, 21 Dec 2014 11:45:53 -0500 (EST) X-Sender-Id: dpreed@reed.com Received: from [100.89.240.116] (18.sub-70-192-10.myvzw.com [70.192.10.18]) (using TLSv1.2 with cipher DHE-RSA-AES256-SHA) by 0.0.0.0:465 (trex/5.4.2); Sun, 21 Dec 2014 16:45:54 GMT User-Agent: K-@ Mail for Android X-Priority: 3 In-Reply-To: References: <6764.1419109075@ccr.org> <68a9aec2-9a5e-4cc0-84d1-3fce8ccc0efb@reed.com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----X0TOWXUKNBKHG9TFE2RD1KNE15Q8EX" Content-Transfer-Encoding: 7bit From: "David P. Reed" Date: Sun, 21 Dec 2014 11:45:51 -0500 To: David Lang Message-ID: <628cf93a-2351-4e44-ab1f-f6b5fa8aae2f@reed.com> Cc: cerowrt-devel@lists.bufferbloat.net, Mike O'Dell Subject: Re: [Cerowrt-devel] Cerowrt-devel Digest, Vol 37, Issue 24 X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 21 Dec 2014 16:46:24 -0000 ------X0TOWXUKNBKHG9TFE2RD1KNE15Q8EX Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable All microwave frequencies heat water molecules, fyi=2E The early ovens used= a klystron that was good at 2=2E4 GHZ because it was available and cheap e= nough=2E But they don't radiate much=2E 5=2E8 GHz was chosen because the ba= nd's primary was a government band at EOL=2E Yes=2E=2E=2E higher frequency= bands have not been used for broadcasting=2E That's because planetary curv= ature can be conquered by refraction near the earth's surface and reflectio= n by the ionosphere=2E That's why power doesn't help were we to use higher = frequencies for broadcasting=2E But data communications is not broadcastin= g=2E So satellite broadcasters can use higher frequencies for broadcasting= =2E And they do, because it's a lot easier to build directional antennas at= higher frequencies=2E Same for radar and GPS=2E Think about acoustics=2E = Higher frequencies from a tweeter propagate through air just as well as lo= wer frequencies from subwoofers=2E But our ears are more directional antenn= ae at the higher frequencies=2E Similar properties apply to EM waves=2E And= low frequencies refract around corners and along the ground better=2E The= steel of a car body does not couple to higher frequencies so it reradiates= low freq sounds better than high freq ones=2E Hence the loud car stereo ba= ss is much louder than treble when the cabin is sealed=2E On Dec 21, 2014,= David Lang wrote: >On Sat, 20 Dec 2014, David P=2E Reed = wrote: > >> Neither 2=2E4 GHZ nor 5=2E8 GHz are absorbed more than other ba= nds=2E >That's an old >> wives tale=2E The reason for the bands' selection= is that they were >available at >> the time=2E The water absorption peak = frequency is 10x higher=2E > >well, microwave ovens do work at around 2=2E4= GHz, so there's some >interaction with >water at that frequency=2E > >> Do= n't believe what people repeat without checking=2E The understanding >of ra= dio >> propagation by CS and EE folks is pitiful=2E Some even seem to thin= k >that RF >> energy travels less far the higher the frequency=2E > >I agr= ee that the RF understanding is poor, but given that it's so far >outside = >their area of focus, that's understandable=2E > >the mistake about higher = frequencies traveling less is easy to >understand, since >higher frequency= transmistters tend to be lower power than lower >frequencies, >there is a= correlation between frequency and distance with commonly >available >equi= pment that is easy to mistake for causation=2E > >David Lang > >> Please do= n't repeat nonsense=2E >> >> On Dec 20, 2014, Mike O'Dell wr= ote: >>> 15=2E9bps/Hz is unlikely to be using simple phase encoding >>> >>>= that sounds more like 64QAM with FEC=2E >>> given the chips available thes= e days for DTV, DBS, >>> and even LTE, that kind of processing is available= >>> off-the-shelf (relatively speaking - compared to >>> writing your own = DSP code)=2E >>> >>> keep in mind that the reason the 2=2E4 and 5=2E8 ISM b= ands >>> are where they are is specifically because of the ready >>> absorp= tion of RF at those frequencies=2E the propagation >>> is *intended* to be = problematic=2E that said, with >>> good-enough antennas mounted with suffic= ient stability >>> and sufficient power on the TX end and a good enough >>>= noise floor on the RX end, one can push a bunch of bits >>> pretty far=2E = >>> >>> Bdale Garbee (of Debian fame) had a 10GHz bent-pipe repeater >>> up= on the mountain above Colo Spgs for quite some time=2E X-band >>> Gunnplex= ers were not hard to come by and retune for the >>> 10GHz ham band=2E i bel= ieve he just FM'ed the Gunnplexer >>> with the output of a 10Mbps ethernet = chip and ran >>> essentially pure Aloha=2E X-band dishes are relatively >>>= small and with just a few stations in the area he had fun=2E >>> >>> = -mo >>> _______________________________________________ >>> Cerowrt-devel m= ailing list >>> Cerowrt-devel@lists=2Ebufferbloat=2Enet >>> https://lists= =2Ebufferbloat=2Enet/listinfo/cerowrt-devel >> >> -- Sent from my Android d= evice with K-@ Mail=2E Please excuse my >brevity=2E > >--------------------= ---------------------------------------------------- > >___________________= ____________________________ >Cerowrt-devel mailing list >Cerowrt-devel@lis= ts=2Ebufferbloat=2Enet >https://lists=2Ebufferbloat=2Enet/listinfo/cerowrt-= devel -- Sent from my Android device with K-@ Mail=2E Please excuse my bre= vity=2E ------X0TOWXUKNBKHG9TFE2RD1KNE15Q8EX Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable All microwave frequencies heat water molecules, fy= i=2E The early ovens used a klystron that was good at 2=2E4 GHZ because it = was available and cheap enough=2E But they don't radiate much=2E 5=2E8 GHz = was chosen because the band's primary was a government band at EOL=2E

Yes=2E=2E=2E higher frequency bands have = not been used for broadcasting=2E That's because planetary curvature can be= conquered by refraction near the earth's surface and reflection by the ion= osphere=2E That's why power doesn't help were we to use higher frequencies = for broadcasting=2E  But data communications is not broadcasting=2E So= satellite broadcasters can use higher frequencies  for broadcasting= =2E And they do, because it's a lot easier to build directional antennas at= higher frequencies=2E Same for radar and GPS=2E

Think about acoustics=2E  Higher frequencies from a tweet= er propagate through air just as well as lower frequencies from subwoofers= =2E But our ears are more directional antennae at the higher frequencies=2E= Similar properties apply to EM waves=2E And low frequencies refract around= corners and along the ground better=2E  The steel of a car body does = not couple to higher frequencies so it reradiates low freq sounds better th= an high freq ones=2E Hence the loud car stereo bass is much louder than tre= ble when the cabin is sealed=2E

On Dec 21, 2014, David Lang <david@lang=2Ehm> wr= ote:
On Sat, 20 Dec 2014, David P=2E Reed wrote:
=
N= either 2=2E4 GHZ nor 5=2E8 GHz are absorbed more than other bands=2E That's= an old
wives tale=2E The reason for the bands' selectio= n is that they were available at
the time=2E The water a= bsorption peak frequency is 10x higher=2E

we= ll, microwave ovens do work at around 2=2E4GHz, so there's some interaction= with
water at that frequency=2E

Don't believ= e what people repeat without checking=2E The understanding of radio
propagation by CS and EE folks is pitiful=2E Some even seem to = think that RF
energy travels less far the higher the fre= quency=2E

I agree that the RF understanding = is poor, but given that it's so far outside
their area o= f focus, that's understandable=2E

the = mistake about higher frequencies traveling less is easy to understand, sinc= e
higher frequency transmistters tend to be lower power = than lower frequencies,
there is a correlation between f= requency and distance with commonly available
equipment = that is easy to mistake for causation=2E

David Lang

Please don't repeat nonsense=2E
=
On Dec 20, 2014, Mike O'Dell <mo@ccr=2Eorg> wrote:=
15=2E9b= ps/Hz is unlikely to be using simple phase encoding

that sounds more like 64QAM with FEC=2E
giv= en the chips available these days for DTV, DBS,
and even = LTE, that kind of processing is available
off-the-shelf (= relatively speaking - compared to
writing your own DSP co= de)=2E

keep in mind that the reason th= e 2=2E4 and 5=2E8 ISM bands
are where they are is specifi= cally because of the ready
absorption of RF at those freq= uencies=2E the propagation
is *intended* to be problemati= c=2E that said, with
good-enough antennas mounted with su= fficient stability
and sufficient power on the TX end and= a good enough
noise floor on the RX end, one can push a = bunch of bits
pretty far=2E

Bdale Garbee (of Debian fame) had a 10GHz bent-pipe repeater
up on the mountain above Colo Spgs for quite some time=2E X-b= and
Gunnplexers were not hard to come by and retune for t= he
10GHz ham band=2E i believe he just FM'ed the Gunnplex= er
with the output of a 10Mbps ethernet chip and ran
essentially pure Aloha=2E X-band dishes are relatively
small and with just a few stations in the area he had fun=2E
-mo

Cerowrt-devel mailing list
Cerowrt-devel@lists=2Ebuf= ferbloat=2Enet
https://lists=2Ebufferbloat=2Enet= /listinfo/cerowrt-devel

-- Sent from my = Android device with K-@ Mail=2E Please excuse my brevity=2E


Cerowrt-devel=
 mailing list
Cerowrt-devel@lists=2Ebufferbloat=2Enet
https://lists=2Ebufferbloat=2Enet/listinfo/cerowrt-=
devel

-- Sent f=
rom my Android device with K-@ Mail=2E Please excuse my brevity=2E


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