Could I use this dish?

I have access to a 7 foot parabolic dish that was used for satellite
receiving. Can I modify it for WIFI, and if so, what type of feed
would I have to build. I am trying to avoid buying an amplifier. Right
now I am using 24dBi grids at 8.8 miles, but the signal is marginal.
I am thinking that I could replace one end with this dish and improve
the signal without further amplification.

Mounting is no problem, it would be on a business roof top, hidden
from the street.

Thanks


Gordon Montgomery
Living Scriptures, Inc
(E-Mail Removed) (anti spam - replace lsi with livingscriptures)
(801) 627-2000

"Gordon Montgomery" <(E-Mail Removed)> wrote...
> I have access to a 7 foot parabolic dish that was used for satellite
> receiving. Can I modify it for WIFI, and if so, what type of feed
> would I have to build. I am trying to avoid buying an amplifier. Right
> now I am using 24dBi grids at 8.8 miles, but the signal is marginal.
> I am thinking that I could replace one end with this dish and improve
> the signal without further amplification.
>
> Mounting is no problem, it would be on a business roof top, hidden
> from the street.
>
> Thanks

I'm thinking an amp(s) would be less headache and cheaper in the long run...

If you insist on persuing this, satellite dishes come in many frequencies
(S, C, Ka, Ku, etc.) find out which one it was on and then work from there
depending on the current feed arrangement (offset, inline, cassegrain)...

http://iwce-mrt.com/ar/radio_feed_de...tion/index.htm

"Darrel Toepfer" <(E-Mail Removed)> wrote in message
newsed0b.17235$(E-Mail Removed) ...
> "Gordon Montgomery" <(E-Mail Removed)> wrote...
> > I have access to a 7 foot parabolic dish that was used for satellite
> > receiving. Can I modify it for WIFI, and if so, what type of feed
> > would I have to build. I am trying to avoid buying an amplifier. Right
> > now I am using 24dBi grids at 8.8 miles, but the signal is marginal.
> > I am thinking that I could replace one end with this dish and improve
> > the signal without further amplification.
> >
> > Mounting is no problem, it would be on a business roof top, hidden
> > from the street.
> >
> > Thanks
>
> I'm thinking an amp(s) would be less headache and cheaper in the long
run...
>
> If you insist on persuing this, satellite dishes come in many frequencies
> (S, C, Ka, Ku, etc.) find out which one it was on and then work from there
> depending on the current feed arrangement (offset, inline, cassegrain)...
>
> http://iwce-mrt.com/ar/radio_feed_de...tion/index.htm
>
>


Amp(s) are expensive, often introduce noise and T/R switching problems and
increase the odds your signal will be intercepted or interfere with others.
Also, even with the special rule for stationary point to point links the
maximum allowable power (in the U.S.) that can be input to a 24dBi antenna
is 250mW. Most bridging equipment is capable of 50 to 100 mW without
amplification, so the most an amplifier can legally add is about 4 to 7 dB.

A parabola is a parabola and while the satellite feed would be useless for
802.11b, the parabolic shape doesn't care about frequency. A satellite
reflector can be refitted with a new feed for 2.4GHz, however, a 7 foot
reflector is capable of outrageous (and illegal) gain at 2.4GHz. Gordon
really needs to find out WHY the signal is marginal with the equipment he's
using. Virtually any 802.11b device can put enough signal into a 24 dBi
antenna for a strong 8.8 mile link assuming the antennas are properly
aligned, transmission line is very short and there is clear line of sight
with a clear Fresnel zone.

Don W.

"Gordon Montgomery" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> In article <SKmcnW9HnJE1SNyiXTWc-(E-Mail Removed)>, "Don W."
<(E-Mail Removed)> wrote:
> >A parabola is a parabola and while the satellite feed would be useless
for
> >802.11b, the parabolic shape doesn't care about frequency. A satellite
>
> That is kind of what I figured, I just don't know enough about antenna
design
> to know what kind of feed to build.
>
> As far as the existing setup, as near as I can tell, there is clear line
of
> sight, and the antennas are correctly aligned. There is a Wireless ISP
> between my two endpoints, but they are not on the center line. I have
spoken
> with them to try to avoid interfering with each other, but of course I
cannot
> completely discount them as a source of interference. I am afraid if I
amp my
> setup, I would just interfere with them too much. That is why I would
like to
> narrow the beam using just the antenna.
>
> I may, of course, not know what I am talking about. So I am counting on
this
> group to set me straight.
>
> Thanks again.
>
>
> Gordon Montgomery
> Living Scriptures, Inc
> (E-Mail Removed) (anti spam - replace lsi with livingscriptures)
> (801) 627-2000

I should also mention you might want to get one of those smaller Primestar
dishes. If you feed an 8 foot reflector correctly, you'll almost certainly
be illegal and it looks really funny to have an 8 foot reflector pointed at
the horizon. If you DO use the 8 foot reflector, almost any feed placed at
the focus will give you a lot of gain. If the beam width of the feed is
very narrow, you won't be using most of the reflector. If the beam width of
the feed is very broad, some of the radiation will miss the reflector, but
with an 8 foot reflector it's kind of hard to miss! Any omni set
perpendicular to the axis of the parabola at the focus will probably give
you more gain than you need even though much of the radiation will miss the
reflector because the reflector has such a large aperture.

Don W.

<(E-Mail Removed)> wrote in message
news:bi09u6$93m$(E-Mail Removed)...
> Don W. <(E-Mail Removed)> wrote:
>
> > Here is a good link on feeding a parabolic reflector:
> > http://www.trevormarshall.com/biquad.htm
>
> On that page, I don't see a specification for the length of the
> copper tube that is the mounting point between the biquad
> reflector and the Primestar feed arm. Do I have to calculate
> the focal point, and make adjustments from the center of the
> dish?

I would assume the focal point to be the position of the active element of
the original Primestar feed. If you don't have the Primestar feed, one way
to determine focal point is to line the reflector with aluminum foil and
point it at your garage door at night from the end of your driveway. Attach
wires to a brake light bulb and connect it to 12 volts and position it
around the obvious location of the old feed. The 'spot' of illumination on
the garage door should intensify when you're near the focus. Even better,
in the daytime with direct sun, put on your sunglasses and put a ping-pong
ball on the end of a stick. Point the reflector at the sun and move the
ping pong ball until you find the bright spot. It's important you know
where to point the reflector and the Primestar is an offset dish, so that
can be a little tricky. Just remember the angle of reflection is the same
as the angle of incidence, so imagine you're banking your shot to the sun
off the reflector with the cue ball at the (approximate) focus.

I'm guessing the author pointed the dish at a 'beacon' signal and moved the
feed in and out until maximum signal was achieved.

>
> > Also, this is a little awkward to read, but here is a table of
> > contents with links to chapters in PDF format:
> > http://www.qsl.net/n1bwt/contents.htm
>
> In reading through these, for a given existing parabola, is it
> correct that the focal point is determined by the f=D^2/16d,
> and that frequency has nothing to do with it?

It's true that frequency has nothing to do with it. Well, I should say it
has nothing to do with the shape of the parabola or the position of the
focus. I don't understand your formula and I don't have time at the moment
to find it in the article, but I'm sure the 'f' is focal point (distance
from reflector to focus) and this formula has something to do with the
optimal relationship between the focal length and the diameter of the
reflector. Any way, the focal point is always determined by the geometry of
the parabola. Interestingly, there's really only one 'parabola' shape.
What appear to be different parabolas with different 'depths' are really
just close-up or wide-angle snapshots of the area of the parabola nearest
the axis. Zoom way out and the parabola appears to be a very deep dish with
the focus close to the reflector. Zoom way in and the parabola appears to
flatten out with the focus far from the reflector.

>
> So I do need to either calculate the f of the Primestar dish,
> or learn the length of the copper tube.

Make the copper tube long enough to move the feed in and out. Position the
feed where it works best. That should be the focus.

>
> Is the phase center alignment then a matter of +/- 1/4", and
> done by trial and error, or is it a measurable distance with
> the BiQuad feed?
>

Was that formula about phase center alignment? I wouldn't even bother with
phase center alignment. Most texts don't even address it because in
comparison with focus alignment it's hardly a factor. If you're shooting
for a 60% efficiency factor and everything else has been optimized and
you're still not quite there, then maybe phase center alignment should be a
consideration. I'd say just move the BiQuad feed in and out until you find
the 'sweet spot' and I'll bet that will be where the BiQuad is at the focus.

>
> --
> ---
> Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

Clarence, I feel like an idiot advising YOU on feeding a parabolic
reflector! You probably have more knowledge and experience than I do.
We're not terribly far from each other (I'm in Concord.) One of these days
we should get together for our own private home-brew antenna shoot-out.
Heck, it would be more fun with more participants. We really should set up
a North Bay/East Bay shoot-out! Think we could get Michael to fly out west
for that? Think David would make a trip to California if he knew how close
Lake County is to the best vineyards in the world?

Don W.

<(E-Mail Removed)> wrote in message
news:bi09u6$93m$(E-Mail Removed)...
> Don W. <(E-Mail Removed)> wrote:
>
> > Here is a good link on feeding a parabolic reflector:
> > http://www.trevormarshall.com/biquad.htm
>
> On that page, I don't see a specification for the length of the copper
tube
> that is the mounting point between the biquad reflector and the Primestar
> feed arm. Do I have to calculate the focal point, and make adjustments
> from the center of the dish?
>
> > Also, this is a little awkward to read, but here is a table of contents
with
> > links to chapters in PDF format:
> > http://www.qsl.net/n1bwt/contents.htm
>
> In reading through these, for a given existing parabola, is it correct
that
> the focal point is determined by the f=D^2/16d, and that frequency has
> nothing to do with it?
>
> So I do need to either calculate the f of the Primestar dish, or learn the
> length of the copper tube.
>
> Is the phase center alignment then a matter of +/- 1/4", and done by
> trial and error, or is it a measurable distance with the BiQuad feed?


Oops

Here is another site to calculate the focal point:
http://www.bigdish.info/mainten/focal.html

Don W. <(E-Mail Removed)> wrote:

If you don't care about the formula, I must not need to care.
Certainly the Primestar arm, whether the LNB is still there or not,
is going to be close enough for the 12v bulb to get it even closer.
I like that solution.

> consideration. I'd say just move the BiQuad feed in and out until you find
> the 'sweet spot' and I'll bet that will be where the BiQuad is at the focus.

I'm probably going to set up my daughter to share a feed from another
apartment building, so my interest in the Primestar dish is practical.
Previously, I had no interest in fixed outdoor links. I saw a Primestar
dish on the side of a house just the other day... where was that?
I have a Dish Networks dish alongside the house. I suppose I could use
that, but the Primestar dish is more graceful, since the Dish still could
be used by someone for Dish.


> Clarence, I feel like an ..... advising YOU on feeding a parabolic
> reflector! You probably have more knowledge and experience than I do.

Gack. No. A few reflectors and lots of measuring ;-)

> We're not terribly far from each other (I'm in Concord.) One of these days
> we should get together for our own private home-brew antenna shoot-out.

I'll stick my biquad in the window as I drive by. Think I can get you from
680 on my way to San Jose?

> Heck, it would be more fun with more participants. We really should set up
> a North Bay/East Bay shoot-out! Think we could get Michael to fly out west
> for that? Think David would make a trip to California if he knew how close
> Lake County is to the best vineyards in the world?

Well stated, with political correctness, not even letting on whether you
think those vineyards are in Napa or Sonoma Counties.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

<(E-Mail Removed)> wrote in message
news:bi171u$4t9$(E-Mail Removed)...
> Don W. <(E-Mail Removed)> wrote:
>
> If you don't care about the formula, I must not need to care.
> Certainly the Primestar arm, whether the LNB is still there or not,
> is going to be close enough for the 12v bulb to get it even closer.
> I like that solution.
>
> > consideration. I'd say just move the BiQuad feed in and out until you
find
> > the 'sweet spot' and I'll bet that will be where the BiQuad is at the
focus.
>
> I'm probably going to set up my daughter to share a feed from another
> apartment building, so my interest in the Primestar dish is practical.
> Previously, I had no interest in fixed outdoor links. I saw a Primestar
> dish on the side of a house just the other day... where was that?
> I have a Dish Networks dish alongside the house. I suppose I could use
> that, but the Primestar dish is more graceful, since the Dish still could
> be used by someone for Dish.
>
>
> > Clarence, I feel like an ..... advising YOU on feeding a parabolic
> > reflector! You probably have more knowledge and experience than I do.
>
> Gack. No. A few reflectors and lots of measuring ;-)
>
> > We're not terribly far from each other (I'm in Concord.) One of these
days
> > we should get together for our own private home-brew antenna shoot-out.
>
> I'll stick my biquad in the window as I drive by. Think I can get you
from
> 680 on my way to San Jose?
>
Holler before you 'get' me... driving by on 680 you might just smack me with
the biquad if it's outside the window. Seriously, if you pass this way,
drop me a line. My email address is right if you remove "NOSPAM" from it.

> > Heck, it would be more fun with more participants. We really should set
up
> > a North Bay/East Bay shoot-out! Think we could get Michael to fly out
west
> > for that? Think David would make a trip to California if he knew how
close
> > Lake County is to the best vineyards in the world?
>
> Well stated, with political correctness, not even letting on whether you
> think those vineyards are in Napa or Sonoma Counties.
>
> --
> ---
> Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

Some Europeans may not agree that the best vineyards in the world are
anywhere near California, but a sunny weekend drive in fall could change
their mind. At least it would be a fun challenge.

Don W.

> > for that? Think David would make a trip to California if he knew how close
> > Lake County is to the best vineyards in the world?

I missed this before but hell yes, any opportunity to pilot around
California is one I'd take up again. I love flying in the US. Not
quite sure I can get this past "Control Panel" though!

David.

"David Taylor" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> > > for that? Think David would make a trip to California if he knew how
close
> > > Lake County is to the best vineyards in the world?
>
> I missed this before but hell yes, any opportunity to pilot around
> California is one I'd take up again. I love flying in the US. Not
> quite sure I can get this past "Control Panel" though!
>
> David.

Let me know if there's anything I can do to bring "Control Panel" around.
Will this help?
http://store.nordstrom.com/category/...776&origin=tab

Don W.