Trying to setup an offset antenna for wifi

Yes. It sorta works:

haven't tried it with a USB adapter yet. Do a Google search for "primestar 802.11" for some ideas.

A few problems you're going to run into:

1. The antenna has to mounted upside-down because the DBS dish mounts were never designed to be pointed at the horizon.

1. Illumination angle of the feed horn or USB antenna must be carefully controlled or lose most of your gain.

2. If working correctly, beamwidth will be about 5-8 degrees which is difficult to aim.

So what results don't you get and how did you test?

put my usb devide just on top of the LNB cuz i understand that there is the focus then i adjust the elevation to 20 o 10 soo the antena look to the horizon then i move side to side to see if i get signal but no good, only 22% of sinal that was the same i get without the antenna soo i think i dont put the usb too well on the focus.

i think i need to try again ppl say me that this could work. I think i dont do it to well on the first try.

i dont see the primestar antena upside-down. the other too comments in dont understand it to well. i will give it a try soo

Lots of problem with your USB device The focus of the antenna is well inside the LMB area That's why the URL you posted had the LMB disassembled Also the metal horn of the LMB will detune the USB antenna if mounted too close Little wonder it doesn't work.

Notice my domain LearnByDestroying.com If you haven't destroyed your wireless then you don't understand how it works.

pizza dish doesn't need to be mounted upside down as you can tilt the swivel base mounting forward to depress the elevation angle.

I don't like using the built in antenna in the USB adapter. I added connector in place of the PIFA antenna and connected it to a biquad antenna. If you like dish antennas, see:

Yeah. That bears repeating. Pretend your USB dongle generates a perfect spherical pattern, like a light bulb without any reflectors. Equal signal strength in xmit in all directions. That's what most USB dongles try to achieve anyway.

Now, you put that spherical illuminator at the focus of a small pizza dish. How much of that spherical illumination does the dish see? Well, that depends on the dish diameter and f/D ratio, but it's not a huge percentage. A crude back of the envelope guess taken from an RCA DBS dish I have sitting in the living room[1][2] yields: Diameter: 18" Focal Len: 12.5"

Therefore, the dish area is: Pi * r^2 = 3.14 * 9^2 = 250 sq in and the surface area of the sphere is: 4 * Pi * r^2 = 4 * 3.14 * 12.5^2 = 1960 sq in.

Therefore, the dish gets only: 250 / 1960 = 0.13 or 13% of the RF that is belched by the USB dongle.

13% left is about 15dB of loss.

The theoretical power gain of a dish is roughly: (circumference / wavelength) ^2 (Pi * 18" / 5" ) ^2 = (3.14 * 18 / 5)^2 = 128 Converting to decibels: Gain = 10 * log(128) = 21 dBi

Throwing in the losses, we have: 21dBi - 3dB (reflection loss) - 15dB (illumination loss) = 3dBi That sucks. That's about the same as a rubber ducky antenna that comes stock with the access points. That's why the illuminator has to be matched fairly carefully with the dish f/D. Why even bother with a USB dongle feed?

Note that is is only for xmit. In receive, the feed illumination angle can be anything that's wider than the dish. Even if mismatched, all the reflected signal from the dish will end up at the feed antenna. However, it transmit, the above illumination problem is fatal.

Light reading:

[1] Doesn't everyone have a DBS antenna sitting in the living room so that everyone smashes their toes on it when blundering through? [2] Who borrowed my metric tape measure?

I forgot to mumble one important item. In receive, the gain of a badly illuminated dish (with overspray) is about the same as if it were properly illuminated. However, because such a feed will pickup signals directly from ALL directions, the dish will have horrible side lobes in the pattern. This will cause it to pickup interference and junk from almost any direction. That's why such an abomination is not sold for receive only dish antennas (DBS) and why they take great care to match the feed to the dish.

here a link of my usb chipset on the FCC database.

i opened mine yesterday and look the same. I search it thru the FCC ID soo it have to be the same chipset.

ok my antena is no a pizza size is a 43.3 inches of Diameter

from the links all give me i will read it, but i notice that in one of the antenna was at 10 angle of elevation i keep mine on 20 that could be a a big error.

i will need to try it again to post new results but here the specs from my antenna.

The Channel Master=AE 1.1m Offset Antenna is a commercial grade product suitable for receive only applications. The reflector is thermoset-molded for strength and surface accuracy. Molded into the rear of the reflector is a network of support ribs which not only strengthens the antenna, but also helps to sustain its critical parabolic shape. The Az/El mount is constructed from heavy-gauge steel to provide a rigid support to the reflector. The Az/El mount secures the antenna to a 2.38 in.O.D.mast.An optional 2.38" universal roof/wall mount is available. A specially formulated powder paint process offers excellent protection from weather-related corrosion.

RF PERFORMANCE Effective Aperture 1.1m (43.3in.) Operating Frequency 11.45 - 12.7 GHz* Polarization LHCP/RHCP* Gain @ 12.5 GHz 41.0 dBi (Typical)

3 dB Beamwidth 1.8=B0 (Typical) Antenna Noise Temperature @ 30=B0 Elevation 45=B0K (Typical)

• Frequence & Polarization Depending on LNBF

MECHANICAL PERFORMANCE Reflector Material Glass Fiber Reinforced Polyester Antenna Optics One-Piece Offset Feed Prime Focus Mount Type Elevation over Azimuth Elevation Adjustment Range 10=B0-70=B0 Continuous Fine Adjustment Azimuth Adjustment Range 360=B0 Continuous Mast Pipe Interface 2.38 in. (60 mm) Outside Diameter Wind Loading Operational 50mi/h (80 km/h) Survival 100 mi/h (160 km/h) Temperature -34=B0C to 52=B0C Humidity 0 to 100% (Condensing) Atmosphere Salt, Pollutants and Contaminant's as Encountered in Coastal and Industrial Areas Solar Radiation 360 BTU/h/ft2 Shock and Vibration As Encountered During Shipping and Handling

I have the DLink DWL-122 that the author of that page used. He notes that he has dis-assembled the DWL-122 so that it will fit, and that it is very important to make the antenna of the DWL-122 perfectly vertical, and correctly positioned, In the photo, you can just see the antenna as a brass bar at the top of the DWL-122 card inserted in the empty LNB housing. I don't know how your USB dongle looks inside. If you just attached the dongle to the outside of the plastic LNB cover, you are quite a bit out of position, and possibly oriented the wrong way as well. The design of this page seems to be on the order of "stick it in and see if it works." Jeff has commented that the USB dongles are not good for painting a dish well. A better dish design might be a combination of a tin can waveguide and dish. This site talks about precision and aiming.

is one.

You could use your USB dongle in the can. Bob Alston's coffee can

Dold's coffee can used the turnpoint calculator to decide where to poke the hole. There are also many haphazard designs on the New Zealand page, using USB dongles. And my favorite, using a "standard" USB adapter, instead of the dongles, is on David Taylor's site.

The common offset feed vertically eliptical DBS dish has an interesting geometry. If you look at the dish from the focus, it appears to be a perfect circle of about 18" in diameter.

The dual LNB horizontally oval dishes, that are about twice as wide as they are high, are the equivalent of two 18" dishes side by side. The reflection from the left LNB goes to the opposite (right) side of the dish. The other side of the dish contributes nothing to the gain. This is necessary to prevent a "daisy" antenna pattern, which will pickup spurious rubbish from other satellites.

The less radically oval DBS dish antennas with dual or triple LNB feeds are a compromise between gain and beamwidth. The design goal is to keep the beamwidth from both LNB's around 2-3 degrees, while the antenna is pointed in the same general direction. If you look at the patterns for dual and triple LNB systems, the 3dB beamwidths are all around 3-4 degress, but the 10dB beamwidth (an indication of side lobes) goes from 3-4 degrees for a single LNB, to perhaps 7 degrees for a triple LNB. It's not a perfect parabola but a good compromise.

Note that all this is for 10-13Ghz. The single LNB dish will probably work at 2.4Ghz, but methinks the parabola is far too distorted with the dual and triple dish designs to insure that the phase center is at one point at 2.4Ghz. I might be wrong, but I'm too lazy to run the models to be sure.

There are lots of ways to aim an offset dish. I do a test adjustment to get the vertical elevation exactly horizontal when mounted on a perfectly vertical pipe. I can then just spin the dish around to wherever it's suppose to point and not worry much about vertical alignment.

Ummm... Melted USB dongle perhaps? You could temporarily cover the dish with aluminium foil and do this experiment. However, I'm not sure I would want to be at the focus when you try it.

I have seen diagrams of the DSS offset dishes that show the true aim on the web. I remember someone stating that they weren't a parabola, but a portion of a parabola, so that they didn't point where they appeared to be pointing. I recall that Primestar dishes always seemed to be pointed at the ground when they were pointed at the satellites.

The indicator on the mast of my DirecTV dish is calibrated for the true aim when mounted to a vertical pole. If you have yours pointing at 20, that's a long ways off from directly horizontal, and this is a very narrow beamwidth. You might move it around while trying to point at a WAP that you can see easily.

If the surface of the dish is optically reflective, you could point it at the sun and see the reflection on the feedhorn.

What kind of gain could one expect from this type of antenna ? Also in playing around with this particular model of USB adapter I was less than impressed with performance as opposed to other actually less well known brands. Any idea of the chipset used on this D-Link USB adapter ?

Jeff Liebermann wrote:

What antenna? Give me a type, size, and feed, and I'll guess(tm) or calculate the gain. Did you catch my previous comments on using a USB dongle as a dish feed?

in all directions, where perhaps 13% of it actually hits the dish and is reflected in the desired direction. I posted an estimate for an

18" dish. You can scale them to whatever size dish you're using.

The original question was about a TRENDnet TEW-424UB. If you have the FCCID number, you can lookup the data at:

Now, which model DLink USB adapter are you talking about? There was no Dlink USB adapter mentioned in previous postings.

Hmmm... Seems like a fun project to try. Maybe keep my coffee warm with a solar heater made from a DBS dish. Maybe a solar concentrator for my boiling water steam turbine generator. Seems like a nice dangerous project to recommend to my science fair project students.

Try adjusting it to 0 degrees. Either the arm that holds the LNB hits the vertical pipe mount, or the dish hits the pipe. Just because the markings go to zero, doesn't mean the mount will work at that angle. I have seen odd mounts that will depress to zero. One can also be fabricated from pipe parts.

I don't have the patience to cook stuff on 2 meter parabolas intended to cook things. An aluminum foil lined parabola, and I wasn't even suggesting that, might cause discomfort if _you_ were at the focus, but for judging where the focus is directed, I don't think there's any danger of melting anything in a short period of time used to note the direction.

I just checked my DirecTV dish. It has a 0-65 degree elevation range.

I was going to mention that there didn't seem to be enough clearance around the "0" mark to actually secure the bolt at that point. It occurs to me that one might mount the dish on a pole at a 45 degree angle. Then the scale might neatly be -45 to +20. I still don't know what the recommendation for 20 degrees would be, unless that yields an elevation of zero with the dish mounted upside down.

Jeff seems to be on an odd bent today. Rather contrarian than helpful.

Another site on this topic:

snipped-for-privacy@XReXXTry> > Try adjusting it to 0 degrees. Either the arm that holds the LNB