I'm sure 130km/80 mile shots are possible - I know a dozen people who work farther than that at 10GHz - though with a LOT of power and 1-3 meter dishes, sporadically, from HIGH elevations (3000+ feet).
Another ham group is doing significant linking at 6 GHz, albeit with 10 watt amplifiers and 1 meter dishes between 2500-4500 foot hilltops.
The numbers just don't add up to do those distances reliably from ground to ground (below 1000 feet is "ground level" to me) with the weather conditions, all of the other clutter and junk we have around here.
The typical SF-Oakland or Berkeley path will have one of a few tall buildings in downtown SF in view and certainly the path parallels the Bay Bridge for most of path. We have consistent trouble getting a 50 watt+6db 450 MHz signal through that and the urban clutter from 1800 feet to good mobile systems, OK, so there's 2-3 db loss in the 150 feet of 7/8" commercial grade cable to the antenna, but still...
Commercial folk have 'proven' the path not to be possible, feasible or at least reliable with the limitations we are under here.
If someone gives me a good location at each end I'd love to try the shot. By good I mean Twin Peaks, Sutro, Coit Tower, TransAmerica, BofA, Mt San Bruno... With coordinates or an address and I'll plot it. I had a 3 story rooftop on the edge of the Bay in Brisbane (CA) with a clear view to Oakland and N. Hayward, but that died with the employer - still I may be able to wrangle a deal.
I'm afraid the Catalina Island example has set the 'bar' way too high for mere mortals to try to achieve on a regular basis.
At 03:31 PM 12/11/2002, evilbunny wrote:
Hello Jim,
Tell that to the guys in Greece that managed to get links happening
between the canary islands :)
I've heard 130km from a consume guy that gave a talk out here a month
ago, and I saw an announcement for 70km a few months before that...
15dBm cards and 24dBi dishes... (no amps)
I know for sure 10km is more then possible, and at 11Mbits, using a
180 8 slot slotted wave guide and a cantenna...
across the bay here, across at least 1 runway at Sydney airport and
there is also something in the vicinity of 120 access points located
at Sydney airport...
I found horizontal polarisation to be a lot more effective then
vertical also...
--
Best regards,
evilbunny mailto:[EMAIL PROTECTED]
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Thursday, December 12, 2002, 7:52:58 AM, you wrote:
JA> Concur with Tim's experience and the issues with doing this.
JA> Additionally, Sprint Broadband Wireless engineers told me they have similar
JA> difficulties trans-Bay from San Bruno (near Sign Hill) to Berkeley,
JA> Oakland, etc. - visual line-of-site but several 'environmental' factors
JA> involved - Bay Bridge, the Bay (waves are highly variable reflectors), the
JA> distance and the marine layer.
JA> Get two hams, two sets of 2.4 GHz gear with signal strength indications,
JA> coordinate antenna alignment live. What we need is a good 100-500mW CW
JA> beacon transmitter and a complimentary receiver with signal strength and
JA> Sinad readouts as a test set...hmmmm....
JA> SF-Berkeley is the toughest shot, over water with the Bay Bridge clutter,
JA> etc. - the rest would be easier from hilltop levels, but from ground or
JA> even building top level - ooooooohhhh - tough call.
JA> Stretching a 300 meter technology at these power level out to 10-30 km is
JA> asking a bit much no matter which antenna, etc. you're using.
JA> At 12:00 PM 12/11/2002, you wrote:
>> 1. Re: Cross-Bay link (Tim Pozar)
>>
>>Message: 1
>>Date: Tue, 10 Dec 2002 11:59:57 -0800
>>From: Tim Pozar <[EMAIL PROTECTED]>
>>To: "Robert R. Ballecer, SJ" <[EMAIL PROTECTED]>
>>Cc: [EMAIL PROTECTED]
>>Subject: Re: [BAWUG] Cross-Bay link
>>
>>On Sat, Dec 07, 2002 at 06:30:56PM -0800, Robert R. Ballecer, SJ wrote:
>> > Has anybody had experience with shooting 802.11b across the bay?
>> I ask
>> > because my organization has properties Fremont, Berkeley, San Jose, Santa
>> > Clara (University), Los Gatos, Los Altos and San Francisco. Each location
>> > is high enough to be able to "see" at least two of the other sites
>> through a
>> > telescope. There are not many practical uses for the link at the moment
>> > (each site already has broadband access) but it might be a nice project for
>> > my free time.
>> >
>> > I was thinking about getting a few of those Senao 200mw cards and
>> use them
>> > in conjunction with some homebrew antennas. Anybody have the equations I
>> > need to figure out how the distance will affect S/N? What says the FCC
>> about
>> > 200mw cards?
>>
>>We tried one 20 mile link with 250mW amplifiers from Sign Hill in
>>South San Francisco to a house in Hayward. The antennas were 24dBi
>>dishes. We were able to get both ends to associate and get some
>>data back and forth, but not consistently. You can see the path
>>profile at:
>>
>> http://www.lns.com/projects/sunsetwireless/paths/Matt2SignHill.pdf
>>
>>Some of the problems we ran into was antenna alignment. 802.11
>>radios do not update C/N data fast enough and the data tends to
>>bounce around. We decided that in order to line up paths you really
>>need to use different transmission gear for antenna alignment such
>>as a carrier wave at the frequency you want and a spectrum analyzer.
>>This also helps as you really have a hard time tracking SS signals
>>on a spectrum analyzer.
>>
>>Of course there are a number of things you need to look at before
>>you get to this point. Looking through a telescope will pass some
>>some tests but you need to look at other things like "refraction"
>>and "fresnel zones" to insure that the data will get from one
>>transmitter to the other. I think there has been some discussion
>>on the list before in "engineering" paths. If not, I can put
>>together one.
>>
>>Tim
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======================================================== Jim Aspinwall - [EMAIL PROTECTED] "lack of (the right) information is a dangerous thing" B.A.R.F. UHF Repeater - 443.750 - San Jose PL 100 - Vaca PL 127.3 ========================================================
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