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 31EDD21F261 for ; Tue, 23 Dec 2014 08:10:58 -0800 (PST) Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp8.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 9373938015F; Tue, 23 Dec 2014 11:10:57 -0500 (EST) X-Virus-Scanned: OK Received: from app2.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by smtp8.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id C18FD3801C7; Tue, 23 Dec 2014 11:10:56 -0500 (EST) X-Sender-Id: dpreed@reed.com Received: from app2.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by 0.0.0.0:25 (trex/5.4.2); Tue, 23 Dec 2014 16:10:57 GMT Received: from reed.com (localhost.localdomain [127.0.0.1]) by app2.wa-webapps.iad3a (Postfix) with ESMTP id AEA98280058; Tue, 23 Dec 2014 11:10:56 -0500 (EST) Received: by apps.rackspace.com (Authenticated sender: dpreed@reed.com, from: dpreed@reed.com) with HTTP; Tue, 23 Dec 2014 11:10:56 -0500 (EST) Date: Tue, 23 Dec 2014 11:10:56 -0500 (EST) From: dpreed@reed.com To: dpreed@reed.com MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_20141223111056000000_99505" Importance: Normal X-Priority: 3 (Normal) X-Type: html In-Reply-To: <1419300989.192428355@apps.rackspace.com> References: <6764.1419109075@ccr.org> <68a9aec2-9a5e-4cc0-84d1-3fce8ccc0efb@reed.com> <628cf93a-2351-4e44-ab1f-f6b5fa8aae2f@reed.com> <29E1C390-9056-463D-885E-7587D71D6E98@gmx.de> <1419300989.192428355@apps.rackspace.com> X-Auth-ID: dpreed@reed.com Message-ID: <1419351056.714111401@apps.rackspace.com> X-Mailer: webmail/11.3.7-RC Cc: cerowrt-devel , 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: Tue, 23 Dec 2014 16:11:27 -0000 ------=_20141223111056000000_99505 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable =0A =0ATypo below - dry air attenuation is 0.0075 dB/kM from the chart. My = leading "1" was a mistake - so the water vapor adds 0.002/0.0075 =3D 27% to= the very small attenuation caused by air, at this frequency.=0A=0AOn Monda= y, December 22, 2014 9:16pm, dpreed@reed.com said:=0A=0A=0A=0AHi Sebastian = -=0A =0ASo reading this chart, which is consistent with my reference materi= als: At 6 GHz, I see additional attenuation of water vapor being -0.002 db/= kM, additional to the dry air attenuation of 10.0075 dB/kM already due to = the atmosphere, at 5.8 GHz.=0A =0ASo at 5 kM (>1 mile in English units), a = signal will be attenuated by about 0.01 dB by water vapour, in addition to = 0.0375 dB of attenuation by the atmosphere. But the attenuation due to pat= h loss at distance d, which is typically log(d**k), or k log(d) - where 2 said:=0A= =0A=0A=0A> Hi David,=0A> =0A> =0A> On Dec 21, 2014, at 17:45 , David P. Ree= d wrote:=0A> =0A> > All microwave frequencies heat water = molecules, fyi. The early ovens used a=0A> klystron that was good at 2.4 GH= Z because it was available and cheap enough. But=0A> they don't radiate muc= h. 5.8 GHz was chosen because the band's primary was a=0A> government band = at EOL.=0A> =0A> Looking at figure 5 of=0A> http://www.itu.int/dms_pubrec/i= tu-r/rec/p/R-REC-P.676-10-201309-I!!PDF-E.pdf it=0A> pretty much looks like= there is higher attenuation at 5GHz compared to 2.4GHz=0A> (roughly 126 = =3D % more attenuation @5GHz due to water in air), so there are some=0A> pr= opagation differences at different frequencies, no?=0A> =0A> >=0A> > Yes...= higher frequency bands have not been used for broadcasting. That's=0A> bec= ause planetary curvature can be conquered by refraction near the earth's=0A= > surface and reflection by the ionosphere. That's why power doesn't help w= ere we to=0A> use higher frequencies for broadcasting. But data communicati= ons is not=0A> broadcasting. So satellite broadcasters can use higher frequ= encies for=0A> broadcasting. And they do, because it's a lot easier to buil= d directional antennas=0A> at higher frequencies. Same for radar and GPS.= =0A> >=0A> > Think about acoustics. Higher frequencies from a tweeter propa= gate through=0A> air just as well as lower frequencies from subwoofers.=0A>= =0A> But look at https://ccrma.stanford.edu/~jos/HarrisJASA66.pdf figure 5= ; air seems=0A> to attenuate sound waves as a function of frequency, so hig= h frequencies do not=0A> travel as far as low frequencies (but are more =E2= =80=9Cefficiently" converted into=0A> heat). But that looks similar to RF w= aves in air (see link above)...=0A> =0A> > But our ears are more directiona= l antennae at the higher frequencies.=0A> =0A> True, once the inter-ear dis= tance is down to 1/4 wavelength there is no useable=0A> intensity and phase= difference between the signal at both ears, hence the=0A> inability to loc= alize the subwoofer (that allows to get a way with one subwoofer=0A> in a s= tereo system). But this depends to a good deal on the inter-ear distance=0A= > (e.g. elephants can reliably localize sounds that humans can not due to t= he=0A> bigger head=E2=80=A6)=0A> =0A> Best Regards=0A> Sebastian=0A> =0A> >= Similar properties apply to EM waves. And low frequencies refract around= =0A> corners and along the ground better. The steel of a car body does not = couple to=0A> higher frequencies so it reradiates low freq sounds better th= an high freq ones.=0A> Hence the loud car stereo bass is much louder than t= reble when the cabin is=0A> sealed.=0A> >=0A> > On Dec 21, 2014, David Lang= wrote:=0A> > On Sat, 20 Dec 2014, David P. Reed wrote:=0A>= >=0A> > Neither 2.4 GHZ nor 5.8 GHz are absorbed more than other bands. Th= at's an old=0A> > wives tale. The reason for the bands' selection is that t= hey were available=0A> at=0A> > the time. The water absorption peak frequen= cy is 10x higher.=0A> >=0A> > well, microwave ovens do work at around 2.4GH= z, so there's some interaction=0A> with=0A> > water at that frequency.=0A> = >=0A> > Don't believe what people repeat without checking. The understandin= g of radio=0A> > propagation by CS and EE folks is pitiful. Some even seem = to think that RF=0A> > energy travels less far the higher the frequency.=0A= > >=0A> > I agree that the RF understanding is poor, but given that it's so= far outside=0A> > their area of focus, that's understandable.=0A> >=0A> > = the mistake about higher frequencies traveling less is easy to understand,= =0A> since=0A> > higher frequency transmistters tend to be lower power than= lower frequencies,=0A> > there is a correlation between frequency and dist= ance with commonly available=0A> > equipment that is easy to mistake for ca= usation.=0A> >=0A> > David Lang=0A> >=0A> > Please don't repeat nonsense.= =0A> >=0A> > On Dec 20, 2014, Mike O'Dell wrote:=0A> > 15.9bps= /Hz is unlikely to be using simple phase encoding=0A> >=0A> > that sounds m= ore like 64QAM with FEC.=0A> > given the chips available these days for DTV= , DBS,=0A> > and even LTE, that kind of processing is available=0A> > off-t= he-shelf (relatively speaking - compared to=0A> > writing your own DSP code= ).=0A> >=0A> > keep in mind that the reason the 2.4 and 5.8 ISM bands=0A> >= are where they are is specifically because of the ready=0A> > absorption o= f RF at those frequencies. the propagation=0A> > is *intended* to be proble= matic. that said, with=0A> > good-enough antennas mounted with sufficient s= tability=0A> > and sufficient power on the TX end and a good enough=0A> > n= oise floor on the RX end, one can push a bunch of bits=0A> > pretty far.=0A= > >=0A> > Bdale Garbee (of Debian fame) had a 10GHz bent-pipe repeater=0A> = > up on the mountain above Colo Spgs for quite some time. X-band=0A> > Gunn= plexers were not hard to come by and retune for the=0A> > 10GHz ham band. i= believe he just FM'ed the Gunnplexer=0A> > with the output of a 10Mbps eth= ernet chip and ran=0A> > essentially pure Aloha. X-band dishes are relative= ly=0A> > small and with just a few stations in the area he had fun.=0A> >= =0A> > -mo=0A> >=0A> > Cerowrt-devel mailing list=0A> > Cerowrt-devel@lists= .bufferbloat.net=0A> > https://lists.bufferbloat.net/listinfo/cerowrt-devel= =0A> >=0A> > -- Sent from my Android device with K-@ Mail. Please excuse my= brevity.=0A> >=0A> >=0A> > Cerowrt-devel mailing list=0A> > Cerowrt-devel@= lists.bufferbloat.net=0A> > https://lists.bufferbloat.net/listinfo/cerowrt-= devel=0A> >=0A> > -- Sent from my Android device with K-@ Mail. Please excu= se my brevity.=0A> _______________________________________________=0A> > Ce= rowrt-devel mailing list=0A> > Cerowrt-devel@lists.bufferbloat.net=0A> > ht= tps://lists.bufferbloat.net/listinfo/cerowrt-devel=0A> =0A> ------=_20141223111056000000_99505 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

 

=0A=0A

T= ypo below - dry air attenuation is 0.0075 dB/kM from the chart. My leading = "1" was a mistake - so the water vapor adds 0.002/0.0075 =3D 27% to the ver= y small attenuation caused by air, at this frequency.

=0A


On Monday, December 22, 2014 9:16pm, dpreed@reed.com said:

=0A
=0A

Hi Sebastian -

=0A

=  

=0A

So reading this chart= , which is consistent with my reference materials: At 6 GHz, I see addition= al attenuation of water vapor being -0.002 db/kM, additional to the dry air= attenuation of  10.0075 dB/kM already due to the atmosphere, at 5.8 G= Hz.

=0A

 

=0A

So at 5 kM (>1 mile in English units), a s= ignal will be attenuated by about 0.01 dB by water vapour, in addition to 0= .0375 dB of attenuation by the atmosphere.  But the attenuation due to= path loss at distance d, which is typically log(d**k), or k log(d) - where= 2<k<4 depending on a variety of factors - will be somewhere between = -122 dB to ~ -190 dB (assuming the antennas are dipoles).

=0A

 

=0A

So the contribution of water vapor at 5.8 GHz is pretty insig= nificant.

=0A

 

=0A

 

=0A



On Sunday, December 21, 2014 2:20pm, "Sebastian = Moeller" <moeller0@gmx.de> said:

=0A
=0A

> Hi David,>
>
> On Dec 21, 2014, at 17:45 , David P. Reed &l= t;dpreed@reed.com> wrote:
>
> > All microwave freque= ncies heat water molecules, fyi. The early ovens used a
> klystron = that was good at 2.4 GHZ because it was available and cheap enough. But
> they don't radiate much. 5.8 GHz was chosen because the band's prima= ry was a
> government band at EOL.
>
> Looking at = figure 5 of
> http://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.676= -10-201309-I!!PDF-E.pdf it
> pretty much looks like there is higher= attenuation at 5GHz compared to 2.4GHz
> (roughly 126 =3D % more a= ttenuation @5GHz due to water in air), so there are some
> propagat= ion differences at different frequencies, no?
>
> >
> > Yes... higher frequency bands have not been used for broadcasti= ng. That's
> because planetary curvature can be conquered by refrac= tion near the earth's
> surface and reflection by the ionosphere. T= hat's why power doesn't help were we to
> use higher frequencies fo= r broadcasting. But data communications is not
> broadcasting. So s= atellite broadcasters can use higher frequencies for
> broadcasting= . And they do, because it's a lot easier to build directional antennas
> at higher frequencies. Same for radar and GPS.
> >
&g= t; > Think about acoustics. Higher frequencies from a tweeter propagate = through
> air just as well as lower frequencies from subwoofers.>
> But look at https://ccrma.stanford.edu/~jos/HarrisJASA66= .pdf figure 5; air seems
> to attenuate sound waves as a function o= f frequency, so high frequencies do not
> travel as far as low freq= uencies (but are more =E2=80=9Cefficiently" converted into
> heat).= But that looks similar to RF waves in air (see link above)...
> > > But our ears are more directional antennae at the higher freq= uencies.
>
> True, once the inter-ear distance is down to = 1/4 wavelength there is no useable
> intensity and phase difference= between the signal at both ears, hence the
> inability to localize= the subwoofer (that allows to get a way with one subwoofer
> in a = stereo system). But this depends to a good deal on the inter-ear distance> (e.g. elephants can reliably localize sounds that humans can not d= ue to the
> bigger head=E2=80=A6)
>
> Best Regards=
> Sebastian
>
> > Similar properties apply to = EM waves. And low frequencies refract around
> corners and along th= e ground better. The steel of a car body does not couple to
> highe= r frequencies so it reradiates low freq sounds better than high freq ones.<= br />> Hence the loud car stereo bass is much louder than treble when th= e cabin is
> sealed.
> >
> > On Dec 21, 2014,= David Lang <david@lang.hm> wrote:
> > On Sat, 20 Dec 2014= , David P. Reed wrote:
> >
> > Neither 2.4 GHZ nor 5.= 8 GHz are absorbed more than other bands. That's an old
> > wive= s tale. The reason for the bands' selection is that they were available
> at
> > the time. The water absorption peak frequency is 1= 0x higher.
> >
> > well, microwave ovens do work at a= round 2.4GHz, so there's some interaction
> with
> > wat= er at that frequency.
> >
> > Don't believe what peop= le repeat without checking. The understanding of radio
> > propa= gation by CS and EE folks is pitiful. Some even seem to think that RF
= > > energy travels less far the higher the frequency.
> ><= br />> > I agree that the RF understanding is poor, but given that it= 's so far outside
> > their area of focus, that's understandable= .
> >
> > the mistake about higher frequencies travel= ing less is easy to understand,
> since
> > higher frequ= ency transmistters tend to be lower power than lower frequencies,
>= > there is a correlation between frequency and distance with commonly a= vailable
> > equipment that is easy to mistake for causation.> >
> > David Lang
> >
> > Please= don't repeat nonsense.
> >
> > On Dec 20, 2014, Mike= O'Dell <mo@ccr.org> wrote:
> > 15.9bps/Hz is unlikely to = be using simple phase encoding
> >
> > that sounds mo= re like 64QAM with FEC.
> > given the chips available these days= for DTV, DBS,
> > and even LTE, that kind of processing is avai= lable
> > off-the-shelf (relatively speaking - compared to
= > > writing your own DSP code).
> >
> > keep in= mind that the reason the 2.4 and 5.8 ISM bands
> > are where th= ey are is specifically because of the ready
> > absorption of RF= at those frequencies. the propagation
> > is *intended* to be p= roblematic. that said, with
> > good-enough antennas mounted wit= h sufficient stability
> > and sufficient power on the TX end an= d a good enough
> > noise floor on the RX end, one can push a bu= nch of bits
> > pretty far.
> >
> > Bdale = Garbee (of Debian fame) had a 10GHz bent-pipe repeater
> > up on= the mountain above Colo Spgs for quite some time. X-band
> > Gu= nnplexers were not hard to come by and retune for the
> > 10GHz = ham band. i believe he just FM'ed the Gunnplexer
> > with the ou= tput of a 10Mbps ethernet chip and ran
> > essentially pure Aloh= a. X-band dishes are relatively
> > small and with just a few st= ations in the area he had fun.
> >
> > -mo
> = >
> > Cerowrt-devel mailing list
> > Cerowrt-devel= @lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinf= o/cerowrt-devel
> >
> > -- Sent from my Android devic= e with K-@ Mail. Please excuse my brevity.
> >
> >> > Cerowrt-devel mailing list
> > Cerowrt-devel@lists.= bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/cerow= rt-devel
> >
> > -- Sent from my Android device with = K-@ Mail. Please excuse my brevity.
> _____________________________= __________________
> > Cerowrt-devel mailing list
> >= Cerowrt-devel@lists.bufferbloat.net
> > https://lists.bufferblo= at.net/listinfo/cerowrt-devel
>
>

=0A
=0A
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