 grohgregDunno. Ask The Chief
join:2001-07-05
Dawson Springs, KY
1 edit | reply to hcwiii
Re: LNB focal point? If you're using the standard Direcway 74cm elliptical reflector, there is no offset to calculate. When the indicator on the side of the bracket says 0 degrees, it's focusing at 0 degrees. The problem you'll likely encounter is noise. Satellite dishes in general have enough parabolic gain to make elevations under ~8 degrees exceedingly noisy. But try anyway, the tower signal may be strong enough to where the S/N ratio is still acceptable to your modem.
And if the modem has a signal strength indicator, use it to optimize your Az/El settings. The point of max receive signal strength should coincide with your strongest signal hitting the tower. Otherwise, you're pointing blind.
//greg//
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HN7000S/98cm Prodelin/2w Osiris/ProPlus - G16/1250H/Germantown - NAT 66.82.187.152/Gateway 66.82.25.10/DNS 66.82.4.12 and 66.82.4.8 - Firefox 3 - AV/Firewalled by NIS2009 |
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hcwiiiPremium
join:2006-03-03
South Wales, NY | Yes, the azimuth scale is there, but it's a pole mount, and only drops down to +10 degrees.
By my calculations, I should need an angle of .3333 degrees or so. (Tower is 6.5 miles distant, and the top of it is 200 feet higher than my dish altitude.)
I did a little experimenting, putting the modem on an extension cable and placing it at the focal point (although not quite - now I know where the focal point really is). I never found any 'sweet spot' that was any better than hanging the modem on the wall indoors.
I'll have to try it again with the antenna in the correct place of focus, and see if I can modify the mount a bit to aim it lower.
Do you know if it's necessary to set up a small shield between the modem and the tower, so it's mainly getting signal that's reflected from the dish? And should this shield be grounded, or signal-grounded (the laptop is obviously not grounded...)?
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Direcway - er Hughesnet Home Pro - DW7000 - AMC9-1290mHz - Win2K - Kerio firewall - Linksys WRT54GS-V7 wireless router
Soon, EVDO! USB727 w/ Cradlepoint MBR1000 wireless router. 1900MHz cellular Wilson roofmount yagi. |
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grohgregDunno. Ask The Chief
join:2001-07-05
Dawson Springs, KY
4 edits | Fabricate a 10 degree wedge and insert it between the dish and the top of the bracket - with the pointy end down. That will get the dish in the vicinity of the horizon when the EL scale says +10. But the reason the scale stops at +10 in the first place, is that noise below 8 degrees I mentioned above.
You are correct in assuming that simply placing the EVDO antenna on the Direcway feedarm will render you vulnerable to multi-path distortion. But in this case a sub-reflector can cause multi-path as well. The trick is to negate any RF - transmit and receive - that is in a direct line between your EVDO antenna and the tower. Grounding the shield should do this. But make sure that it's the shield only that's grounded - you don't want parasitic grounding of the main reflector. I'd electrically isolate the shield from the feedarm and THEN ground the shield. RF from the tower couldn't then hit the EVDO antenna except on the bounce from the dish and RF from the EVDO antenna would only reach the tower on a bounce from the dish.
But this assumes you can actually get a good "focus" between the parabola and the tower. The alternative may be simply to put up with the multi-path distortion and the ground noise.
//greg//
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HN7000S/98cm Prodelin/2w Osiris/ProPlus - G16/1250H/Germantown - NAT 66.82.187.152/Gateway 66.82.25.10/DNS 66.82.4.12 and 66.82.4.8 - Firefox 3 - AV/Firewalled by NIS2009 |
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hcwiiiPremium
join:2006-03-03
South Wales, NY | Excellent Greg, I sure appreciate your input.
I'll work on it, and post any results here....
The nice thing is that Verizon has recently acquired a permit to install a tower about a mile down the hill from my house. I'm hoping that they'll get it up this spring or summer, though I don't really know how long it takes these things to happen. When that's in, I hope to get 5 bars with no outside antenna. Then I can mount the dish on top of my car and use it for travel  ....
Thanks for your help!
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No longer Hughesnet Home Pro - DW7000 - AMC9-1290mHz -
Now EVDO! Verizon USB727 w/ Cradlepoint MBR1000 wireless router.
Win2K - Kerio/Sunbelt firewall |
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