From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp65.iad3a.emailsrvr.com (smtp65.iad3a.emailsrvr.com [173.203.187.65]) (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 3546E21F1E4 for ; Mon, 22 Dec 2014 18:16:30 -0800 (PST) Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp25.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 7A646180270; Mon, 22 Dec 2014 21:16:29 -0500 (EST) X-Virus-Scanned: OK Received: from app8.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by smtp25.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 4472F180174; Mon, 22 Dec 2014 21:16:29 -0500 (EST) X-Sender-Id: dpreed@reed.com Received: from app8.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 02:16:29 GMT Received: from reed.com (localhost.localdomain [127.0.0.1]) by app8.wa-webapps.iad3a (Postfix) with ESMTP id 2F86D28005A; Mon, 22 Dec 2014 21:16:29 -0500 (EST) Received: by apps.rackspace.com (Authenticated sender: dpreed@reed.com, from: dpreed@reed.com) with HTTP; Mon, 22 Dec 2014 21:16:29 -0500 (EST) Date: Mon, 22 Dec 2014 21:16:29 -0500 (EST) From: dpreed@reed.com To: "Sebastian Moeller" MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_20141222211629000000_39843" Importance: Normal X-Priority: 3 (Normal) X-Type: html In-Reply-To: <29E1C390-9056-463D-885E-7587D71D6E98@gmx.de> 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> X-Auth-ID: dpreed@reed.com Message-ID: <1419300989.192428355@apps.rackspace.com> X-Mailer: webmail/11.3.7-RC Cc: Mike O'Dell , cerowrt-devel 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 02:16:59 -0000 ------=_20141222211629000000_39843 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable =0AHi Sebastian -=0A =0ASo reading this chart, which is consistent with my = reference materials: 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 En= glish 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 attenu= ation due to path loss at distance d, which is typically log(d**k), or k lo= g(d) - where 2 said:=0A=0A=0A=0A> Hi David,=0A> =0A> =0A> On Dec 21, 2014, at 17:= 45 , David P. Reed wrote:=0A> =0A> > All microwave freque= ncies heat water molecules, fyi. The early ovens used a=0A> klystron that w= as good at 2.4 GHZ because it was available and cheap enough. But=0A> they = don't radiate much. 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/itu-r/rec/p/R-REC-P.676-10-201309-I!!PDF-E.pdf it=0A> prett= y 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> propagation differences at different frequencies, no?=0A> =0A>= >=0A> > Yes... higher frequency bands have not been used for broadcasting.= That's=0A> because 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 were we to=0A> use higher frequencies for broadcasting. But d= ata communications is not=0A> broadcasting. So satellite broadcasters can u= se higher frequencies for=0A> broadcasting. And they do, because it's a lot= easier to build directional antennas=0A> at higher frequencies. Same for r= adar and GPS.=0A> >=0A> > Think about acoustics. Higher frequencies from a = tweeter propagate through=0A> air just as well as lower frequencies from su= bwoofers.=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 freq= uency, so high frequencies do not=0A> travel as far as low frequencies (but= are more =E2=80=9Cefficiently" converted into=0A> heat). But that looks si= milar to RF waves in air (see link above)...=0A> =0A> > But our ears are mo= re directional antennae at the higher frequencies.=0A> =0A> True, once the = inter-ear distance is down to 1/4 wavelength there is no useable=0A> intens= ity and phase difference between the signal at both ears, hence the=0A> ina= bility to localize the subwoofer (that allows to get a way with one subwoof= er=0A> in a stereo system). But this depends to a good deal on the inter-ea= r distance=0A> (e.g. elephants can reliably localize sounds that humans can= not due to the=0A> bigger head=E2=80=A6)=0A> =0A> Best Regards=0A> Sebasti= an=0A> =0A> > Similar properties apply to EM waves. And low frequencies ref= ract around=0A> corners and along the ground better. The steel of a car bod= y does not couple to=0A> higher frequencies so it reradiates low freq sound= s better than high freq ones.=0A> Hence the loud car stereo bass is much lo= uder than treble 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 othe= r bands. That's an old=0A> > wives tale. The reason for the bands' selectio= n is that they were available=0A> at=0A> > the time. The water absorption p= eak frequency is 10x higher.=0A> >=0A> > well, microwave ovens do work at a= round 2.4GHz, so there's some interaction=0A> with=0A> > water at that freq= uency.=0A> >=0A> > Don't believe what people repeat without checking. The u= nderstanding 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 fr= equency.=0A> >=0A> > I agree that the RF understanding is poor, but given t= hat 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 lowe= r power than lower frequencies,=0A> > there is a correlation between freque= ncy and distance with commonly available=0A> > equipment that is easy to mi= stake for causation.=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> > tha= t sounds more like 64QAM with FEC.=0A> > given the chips available these da= ys for DTV, DBS,=0A> > and even LTE, that kind of processing is available= =0A> > off-the-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 of RF at those frequencies. the propagation=0A> > is *intended* = to be problematic. that said, with=0A> > good-enough antennas mounted with = sufficient stability=0A> > and sufficient power on the TX end and a good en= ough=0A> > noise floor on the RX end, one can push a bunch of bits=0A> > pr= etty far.=0A> >=0A> > Bdale Garbee (of Debian fame) had a 10GHz bent-pipe r= epeater=0A> > up on the mountain above Colo Spgs for quite some time. X-ban= d=0A> > Gunnplexers 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 ethernet chip and ran=0A> > essentially pure Aloha. X-band dishes = are relatively=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-d= evel@lists.bufferbloat.net=0A> > https://lists.bufferbloat.net/listinfo/cer= owrt-devel=0A> >=0A> > -- Sent from my Android device with K-@ Mail. Please= excuse my brevity.=0A> >=0A> >=0A> > Cerowrt-devel mailing list=0A> > Cero= wrt-devel@lists.bufferbloat.net=0A> > https://lists.bufferbloat.net/listinf= o/cerowrt-devel=0A> >=0A> > -- Sent from my Android device with K-@ Mail. P= lease excuse my brevity.=0A> ______________________________________________= _=0A> > Cerowrt-devel mailing list=0A> > Cerowrt-devel@lists.bufferbloat.ne= t=0A> > https://lists.bufferbloat.net/listinfo/cerowrt-devel=0A> =0A> ------=_20141222211629000000_39843 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

Hi Sebastian -

=0A

 

=0A

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

= =0A

 

=0A

So at 5 kM (>1 mile = in English units), a signal will be attenuated by about 0.01 dB by water va= pour, 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 con= tribution of water vapor at 5.8 GHz is pretty insignificant.

=0A

 

=0A

 

=0A=0A



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

=0A
=0A

> Hi David,
>
>
> On Dec 21, 2014, a= t 17:45 , David P. Reed <dpreed@reed.com> wrote:
>
>= > All microwave frequencies 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 chose= n because the band's primary was a
> government band at EOL.
&= gt;
> Looking at figure 5 of
> http://www.itu.int/dms_pubr= ec/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 attenuation @5GHz due to water in air), so there a= re some
> propagation differences at different frequencies, no?
>
> >
> > Yes... higher frequency bands have no= t been used for broadcasting. That's
> because planetary curvature = can be conquered by refraction near the earth's
> surface and refle= ction by the ionosphere. That's why power doesn't help were we to
>= use higher frequencies for broadcasting. But data communications is not> broadcasting. So satellite 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 G= PS.
> >
> > Think about acoustics. Higher frequencies= from a tweeter propagate through
> air just as well as lower frequ= encies from subwoofers.
>
> But look at https://ccrma.stan= ford.edu/~jos/HarrisJASA66.pdf figure 5; air seems
> to attenuate s= ound waves as a function of frequency, so high frequencies do not
>= travel as far as low frequencies (but are more =E2=80=9Cefficiently" conve= rted into
> heat). But that looks similar to RF waves in air (see l= ink above)...
>
> > But our ears are more directional a= ntennae at the higher frequencies.
>
> True, once the inte= r-ear distance is down to 1/4 wavelength there is no useable
> inte= nsity 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 o= n the inter-ear distance
> (e.g. elephants can reliably localize so= unds that humans can not due to the
> bigger head=E2=80=A6)
&g= t;
> Best Regards
> Sebastian
>
> > Si= milar properties apply to EM waves. And low frequencies refract around
> corners and along the ground better. The steel of a car body does not= couple to
> higher frequencies so it reradiates low freq sounds be= tter than high freq ones.
> Hence the loud car stereo bass is much = louder than treble when the cabin is
> sealed.
> >
= > > On Dec 21, 2014, David Lang <david@lang.hm> wrote:
>= ; > On Sat, 20 Dec 2014, David P. Reed wrote:
> >
> &= gt; Neither 2.4 GHZ nor 5.8 GHz are absorbed more than other bands. That's = an old
> > wives tale. The reason for the bands' selection is th= at they were available
> at
> > the time. The water abso= rption peak frequency is 10x higher.
> >
> > well, mi= crowave ovens do work at around 2.4GHz, so there's some interaction
&g= t; with
> > water at that frequency.
> >
> &g= t; Don't believe what people repeat without checking. The understanding of = radio
> > propagation by CS and EE folks is pitiful. Some even s= eem to think that RF
> > energy travels less far the higher the = frequency.
> >
> > I agree that the RF understanding = is poor, but given that it's so far outside
> > their area of fo= cus, that's understandable.
> >
> > the mistake about= higher frequencies traveling less is easy to understand,
> since> > higher frequency transmistters tend to be lower power than lo= wer frequencies,
> > there is a correlation between frequency an= d distance with commonly available
> > 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 more like 64QAM with FEC.
> > given the = chips available these days for DTV, DBS,
> > and even LTE, that = kind of processing is available
> > off-the-shelf (relatively sp= eaking - compared to
> > writing your own DSP code).
> &= gt;
> > keep in mind that the reason the 2.4 and 5.8 ISM bands> > are where they are is specifically because of the ready
= > > absorption of RF at those frequencies. the propagation
> = > is *intended* to be problematic. that said, with
> > good-e= nough antennas mounted with sufficient stability
> > and suffici= ent power on the TX end and a good enough
> > noise floor on the= RX end, one can push a bunch of bits
> > pretty far.
> = >
> > Bdale Garbee (of Debian fame) had a 10GHz bent-pipe rep= eater
> > up on the mountain above Colo Spgs for quite some time= . X-band
> > Gunnplexers were not hard to come by and retune for= the
> > 10GHz ham band. i believe he just FM'ed the Gunnplexer<= br />> > with the output of a 10Mbps ethernet chip and ran
> = > essentially pure Aloha. X-band dishes are relatively
> > sm= all and with just a few stations in the area he had fun.
> >
> > -mo
> >
> > Cerowrt-devel mailing list> > Cerowrt-devel@lists.bufferbloat.net
> > https://lis= ts.bufferbloat.net/listinfo/cerowrt-devel
> >
> > -- = Sent from my Android device with K-@ Mail. Please excuse my brevity.
&= gt; >
> >
> > Cerowrt-devel mailing list
>= > Cerowrt-devel@lists.bufferbloat.net
> > https://lists.buff= erbloat.net/listinfo/cerowrt-devel
> >
> > -- Sent fr= om my Android device with K-@ Mail. Please excuse my brevity.
> ___= ____________________________________________
> > Cerowrt-devel m= ailing list
> > Cerowrt-devel@lists.bufferbloat.net
> &g= t; https://lists.bufferbloat.net/listinfo/cerowrt-devel
>
>= ;

=0A
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