Off Grid Living / Camping > Off Grid Living / Alternative Housing
MOVED - Satellite Dish Wifi
Seth7:
This has a bunch of useful information .. none of which is helpful to the task im looking for ...
http://www.lecad.fs.uni-lj.si/~leon/other/wlan/biquad/
rossw:
--- Quote from: Seth7 on June 22, 2013, 08:11:56 pm ---Finding the best distance from the dish to couple the most signal for the Bi-Quad is a missing factor.
--- End quote ---
Parabolic dishes (lets just talk about prime-focus for a moment, because they're more intuitive) are not rocket science.
Parabolic dishes have a given FD ratio, which determines exactly where the perfect focus is for a given diameter dish.
You can move in and out from there along the focus axis to maximise the effectiveness of the dish to suit your feed.
Ideally, you want a feed that produces a perfect conical radiation. Reality is that most antennas have different radiation in the H and E plane, so it'll be a compromise.
If your antenna/feed has a radiation angle of (lets say) 30 degrees. If your feed is too close to the dish, you are under-illuminating it and only a part of your parabolic surface is contributing.
If your feed is too far away, you are over-illuminating the dish, and some of your power is going straight past the dish and being wasted..
Perfect illumination sees all the dish being used. The ideal focus can be calculated, but it's still a compromise and fairly easily found by experimentation, measuring the signal strength. It's arguably easier to use the dish in a receive mode with a source quite some distance away (preferably hundreds of wavelengths away), fix the dish and adjust the feed distance for optimum signal strength.
MadScientist267:
Thanks for all the input so far - keep it coming, the picture its getting clearer and clearer... ;)
One beautiful aspect to this, while I do indeed have the LNB and arms for both dishes, I too am confused about exactly where the focal point lies, but I have a whole bunch of leftover foam scraps from insulating the van, which make easy targets for simple fabrication of mounting shims and the like.
Looking down the barrel of an LNB however, there is the horn, then a short tube, and then what I can only imagine is the antenna element. On the triple LNB, these elements are about 2 inches or so behind the weather cap that goes over the horn.
So, does this mean that the focal points are on the elements themselves, or is it closer to the dish, right at the threshold of the horn (which then becomes a waveguide) where focus is no longer an issue?
I'd post a pic but I don't have one handy at the moment, but hopefully in the mean time someone will have seen the internal structure of an LNB feed horn and it will make sense...
Steve
Seth7:
This is OT .. but still fun ...
http://www.youtube.com/watch?feature=player_embedded&v=TtzRAjW6KO0#t=0s
MadScientist267:
Ah ok posts clashed Ross....
Ok so just as I'm seeing with the dipole, the biquad is going to have yet a different ideal focal length than the dipole and original LNB?
Steve
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