A calculation was made estimating the worst-case contribution of 802.11 equipment in the footprint and it raised the noise floor at the satellite, but not by much. At S-band, a 2-foot dish gives 26 dBic of gain and with 4 parallel 1 W amplifier ICs ($5 each) this provides 1600 W EIRP. We'd like to allow use of WiFi parts as most mcrowave power transistors cost over $100 each.
I originally argued for an L-band digital uplink but was persuaded that it's too risky.
73,
John KD6OZH
----- Original Message ----- From: "Greg D." ko6th_greg@hotmail.com To: kd6ozh@comcast.net; domenico.i8cvs@tin.it; amsat-bb@amsat.org Sent: Monday, September 11, 2006 05:58 UTC Subject: Re: [amsat-bb] Re: S band and Eagle: an appeal for a higherleveldiscussion
Hi John,
My concern on the uplink side is that any individual interferer is low
power
but there will be many tens of thousands of them wihin the field of view
of
the satellite. If there are enough of them on the ground to be a problem
in
the immediate vicinity of a station, then surely they would be a problem
for
the satellite looking down. I agree that we can probably scream louder
than
the collective noise, but how we get the signal to scream that loud is another question. Someone pointed out that power amps are going to be
cheap
because of all the WiFi gear out there, and that's probably true, but
we're
not going to get to a kw EIRP from one without a pretty big antenna (1W to 1KW is 30 db, right?). And, there aren't any up-converters coming free
like
we had with the MMDS downconverters that we all found. We have ready
access
to equipment and power on 2m and 70cm, making U and V uplinks easy and
wide
spread.
On the downlink side, my own opinion is that there will be a natural saturation point of 2.4 ghz equipment that is below the projections. One
of
the reasons I have for this opinion is that self-interference and
marketing
will drive many to 5 ghz (we see cordless phones already packing up and headed there now), and the demands on WiFi will force the move to 5 ghz
for
its non-overlaping channels. 802.11a is already there, and 802.11n is coming (pre-n stuff is on 2.4, but the standard also covers 5 ghz). One cranked-up 802.11n channel covers 40 mhz, which pretty much wipes out half of the 2.4 ghz allocation, so it's not going to live long down there.
The other factor is that there is a limit to how many gizmos we will put
up
with. The manufacturers have this happy stockholder-driven picture of everyone wandering around with a thingy sticking out of their ear, bluetoothed to a thingy on their belt, which talks to another thingy on their belt, in their pocket, on their wrist, the car naviation system, the home entertainment system, keyboard, mouse, coffee maker, and so on, ad nausium (with emphasis on the nausium part). My prediction is that there will be a revolt at some point, with too many gadgets being thrown at us, and people will buy ONE device that has a bunch of these things all built
in
(without the many wireless links). Either that, or our attention
deficient
society will tire of this line of business, and the rest of the gadgets
will
sit turned off in the drawer, on the shelf, or in the land fill, awaiting the day when some future archaeologist digs them up and wonders what on Earth we were thinking. The area networks, replacing the ill-fated BPL systems, will be on licensed spectrum, because (as my own internet service provider is finding out) unlicensed spectrum is too crowded to build a business around. All of this adds up to much less 2.4 ghz interference.
Just my own opinion,
Greg KO6TH
----Original Message Follows---- From: "John B. Stephensen" kd6ozh@comcast.net To: "i8cvs" domenico.i8cvs@tin.it,"Greg D." ko6th_greg@hotmail.com,"AMSAT-BB" amsat-bb@amsat.org Subject: Re: [amsat-bb] Re: S band and Eagle: an appeal for a higherleveldiscussion Date: Mon, 11 Sep 2006 03:20:05 -0000
For 13 cm uplinks we can just overpower the interferers. The WiFi interference is attenuated at the same rate as the uplink signal. Most interferers are 10 mW EIRP or less and the uplink is 1 KW EIRP or more.
For a 13 cm downlink, increasing the power level is impractical as solar panels are very expensive.
73,
John KD6OZH
----- Original Message ----- From: "i8cvs" domenico.i8cvs@tin.it To: "Greg D." ko6th_greg@hotmail.com; "AMSAT-BB" amsat-bb@amsat.org Sent: Monday, September 11, 2006 02:11 UTC Subject: [amsat-bb] Re: S band and Eagle: an appeal for a higherleveldiscussion
----- Original Message ----- From: "Greg D." ko6th_greg@hotmail.com To: amsat-bb@amsat.org Sent: Sunday, September 10, 2006 8:40 PM Subject: [amsat-bb] Re: S band and Eagle: an appeal for a higher leveldiscussion
If 2.4 ghz pollution is going to be a problem for stations on the
ground
who
are looking up (and away from) the noise, how is it possible that a satellite in the sky looking down on half of a planet's worth of 2.4
ghz
noise, is going to be able to pick out one earthly station over the
din?
This is totally backwards in my mind.
Greg KO6TH
Hi Greg, KO6TH
It is possible !
During the test of 23 Feb 2003 AO40 was looking down on half of the planet's using his S1 high-gain dish connected to the S1 RX worth of noise on 2400.475 MHz and was able to pick out G3WDG and i8CVS for the first experiment on S/K band in wich an amateur satellite was succesfully tested the first time to receive over the dim an uplink at 2400.475 MHz
So it is totally backward in my mind why the S band is considered a
sewer
three years now from the above test.
If you look at the following page you have the complete report written
by
G3WDG and a wave-file showing how clean where both signals over the noise on SSB
--
Quoting Stacey E. Mills W3SM [amsat-bb] AO-40 Update, 2003-02-23
Two tests were performed on AO-40 today.
The second test involving the S-band receivers was completely successful. Extremely strong downlink signals were possible using
S-band
uplink to K-band downlink. Charlie (G3WDG) phoned me and I heard beautiful downlink signals from his ~5 watt uplink to S1. S2 was also active, but because of its higher, less common frequency (2446 MHz), it
may
not have been tested. The S1 Rx uses the S1 Tx high-gain dish, and the
S2
Rx uses the 5 turn helix used by the S2 Tx, so signals would not be as strong through S2 at low squint. More information will undoubtedly be posted on this by the participants, but special thanks to Charlie
(G3WDG),
Mike (N1JEZ), and Dom (I8CVS), and any others who participated in this successful test.
The S1 Rx can certainly be listed as fully functional. We will await further testing/info. on the S2 Rx.
--W4SM for the AO-40 Command Team
--
Quoting Charlie G3WDG [amsat-bb] AO-40 S/K Test
All,
I have posted some info on the tests here, including some recordings of G3WDG and I8CVS's S-Band signals received on K-Band.
http://www.g3wdg.free-online.co.uk/s_ktest.htm
73
Charlie G3WDG
--
Best 73" de
i8CVS Domenico
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